CoE ATM - Research Highlights 2017

The development of chambers at SMEAR II: The pursuit of combining novel scientific methodology, reliability and ease of use J. Aalto, P. Kolari, A. Vanhatalo, H. Aaltonen, L. Kulmala, T. Pohja, P. Hari, J. Bäck

Various types of measurement chambers, enclosing a confined part of ecosystem under observation, have been utilized at Hyytiälä forestry field station for almost 50 years.

The chambers used at SMEAR stations can be divided into three groups, based on the study object: Soil chambers, stem chambers and shoot chambers.

When the aim is to conduct automated, continuous measurements, the standard should be the best technical solutions and high quality assembly and finishing.

As the best solutions do not necessarily turn up at once, the chamber development is a continuous, self-reconstructing process, which produces better and better solutions in the course of years.

Quality control by performance audits improving the quality of atmospheric greenhouse gas measurements H. Aaltonen, K. Saarnio, J. Hatakka, T. Mäkelä, J. Rainne, M. Ramonet, O. Laurent, D. Rzesanke, T. Laurila

ICOS is a high precision long-term network of stations measuring greenhouse gas concentrations and fluxes.

To ensure the high quality of the data, quality control is essential part of the measurement procedures in ICOS.

MobileLab, ICOS internal quality tool, is equipped with state of the art instrumentation and WMO scale standard gases for the greenhouse gas measurements.

The main task of the MobileLab is to perform audits for ICOS atmospheric stations and thus ensure the high performance of the stations measurements.

Towards aerosol climatology using nighttime AOD measurements V. Aaltonen, E. Rodriguez, G. de Leeuw

Ground based AOD is normally measured using passive photometry which exploits sun as a light target.

Recent technical achievements in instrument technology have led to development of a Lunar photometer. CIMEL CE-318T is able to measure both during day and night times. During night, it uses Moon as light target.

We tested how well the AODs observed in late evening and early morning match with those measured at night. Taking into account the instrument accuracy, the data nighttime data agrees reasonably well with the daytime data.

Long-term field measurement with particle size magnifier (psm) L.R. Ahonen, J. Kangasluoma, K. Lehtipalo. T. Petäjä and M. Kulmala

Sampling is one of the key aspects in sub-3 nm aerosol particle measurements. Small newly formed particles will diffuse rapidly and are lost into the sampling lines if special care is not taken.

Lab measurements show that, when the PSM is used with settings that cause homogenous droplet formation inside the instrument, detection efficiency can be correlated to the background counts

One of the biggest factors for long-term PSM measurement accuracy is the condition of the CPC. There are several types of malfunctions that might happen to it, which will affect to the measured particle concentrations.

It is important to use consistent methods in the atmospheric measurements. For now, there is still a need to further improve the long-term measurements with PSMs and furthermore, come up with consistent way to perform calibrations for different environments.

Figure 1. Detection efficiency of the PSM as a function of background counts. Measurement is with THA+ ion with 1.47 nm mobility diameter (Ude and de la Mora, 2005). PSM’s saturator temperature indicated with color.

The first comparison of surface exchange rates between Siikaneva fen and bog sites P. Alekseychik, I. Mammarella, E.-S. Tuittila and T. Vesala

A new modeling method producing smooth response function parameter timeseries was developed for the eddy-covariance CO2 and CH4 data, and tested on the Siikaneva-1,2 fen and bog data.

Growing season cumulative values derived from the Siikaneva-1,2 eddy-covariance data on CO2 fluxes demonstrate widely different photosynthesis and respiration rates that surprisingly lead to comparable net fluxes.

The response function parameters of the gross primary productivity, ecosystem respiration and CH4 efflux appear to vary intensively on both a seasonal and weekly scales, probably being driven by temperature, leaf area index, water table and precipitation variations.

A new method to measure chlorophyll a fluorescence spectra emitted from whole tree canopies J. Atherton, W. Liu, A. Porcar-Castell

- Chlorophyll a fluorescence, a multi-scale biomarker of plant productivity, is emitted from plant leaves as a broad continuous spectrum in the red to near infrared wavelengths. Although fluorescence spectra are measurable for leaves in the laboratory, at larger scales solar excited chlorophyll fluorescence (SIF) is typically retrieved from remote sensing platforms only in narrow wavelength limited bands using the Fraunhofer Line Depth method. Innovative methods are therefore required to link the various scales of fluorescence measurements, in particular the wavelength-variant influence of canopy structure on canopy SIF requires attention.

- Here we show how chlorophyll a fluorescence spectra can be measured for whole tree canopies. The main requirements are a strong enough wavelength restricted light source, darkness (i.e. night-time measurements) and a standard field spectrometer.

- Our results show that the measured canopy emission spectra are dependent on the illumination spectra, and also generally skewed towards the far red peak.

Resolving the urban micrometeorology with large-eddy simulation M. Auvinen, L. Järvi, S. Boi, A. Hellsten, T. Vesala

Pursuing an improved understanding of the turbulent interactions between the atmospheric boundary layer (ABL) flow and built environments, which are characterized by structural, thermal and material complexity, is an essential goal in urban micrometeorology. In order to obtain reliable predictions on how local changes in the urban plan influence the local conditions, the relevant turbulence physics that lie at the core of the studied phenomena have to be resolved. The proposed numerical sensitivity study seeks to clarify the most central level of detail (LOD) issues relating to urban flow modelling by performing a series of LES simulations where the LOD of the following modelling aspects are varied: (1) Surface temperature distribution, (2) leaf area density distribution, (3) ABL height, (4) inlet boundary condition and (5) LES resolution. As an outcome, the simulations and the subsequent analysis will reveal original information that will be essential when LES solver validation is sought in a real urban setting.

On measurements and spatial distribution of light absorbing aerosols in the Arctic J. Backman, L. Schmeisser, A. Virkkula, J.A. Ogren, E. Asmi, S. Starkweather, S. Sharma, K. Eleftheriadis, T. Uttal, A. Jefferson, M. Bergin, A. Makshtas, and H. Lihavainen

Instruments measuring black carbon in the Arctic need to have a low detection limit due to the low concentrations. The detection limit one such instrument can be lowered by simple data post-processing. Using data from six Arctic stations, a footprint was calculated using back-trajectories from the HYSPLIT model.

Lowest concentration were calculated to be over Greenland and south of the Svalbard archipelago. The highest concentrations were associated with air masses originating in the East.

Figure 1. Footprint of light absorption coefficients (σap) using data from the six Arctic stations at a wavelength of 700 nm. The figure comprise back-trajectories where the trajectory altitude was less than 500 metres above ground level. Red stars mark the locations of the respective stations. Latitude and longitude grid lines are spaced 15o and 30o apart, respectively. Grid cells that have fewer than 5 trajectory overpasses have been omitted.

Figure 1. Footprint of light absorption coefficients (σap) using data from the six Arctic stations at a wavelength of 700 nm. The figure comprise back-trajectories where the trajectory altitude was less than 500 metres above ground level. Red stars mark the locations of the respective stations. Latitude and longitude grid lines are spaced 15o and 30o apart, respectively. Grid cells that have fewer than 5 trajectory overpasses have been omitted.

Measurements of biogenic volatile organic compounds in the atmosphere by solid-phase microextraction Arrow and gas chromatography-mass spectrometry L. M.F. Barreira, G. Duporté, T. Rönkkö, L. Schulman, E. Heikkinen, J. Parshintsev, K. Hartonen, M. Jussila, M. Kulmala, M-L. Riekkola

A novel solid-phase microextraction Arrow system combined with gas chromatography-mass spectrometry was employed for the field measurement of biogenic volatile organic compounds (BVOCs) in the atmosphere.

The most abundant monoterpenes and aldehydes were successfully measured.

The extraction efficiency for monoterpenes and aldehydes with the SPME Arrow was approximately two times higher than the one with the SPME fiber, with exception for aldehydes during the field campaign where a 7-fold enhancement was observed.

Meteorological parameters influenced the amounts of studied BVOCs in the atmosphere, but laboratory tests showed that an increase in temperature and relative humidity causes a decrease in the extracted amounts of BVOCs, especially when PDMS/Carbon WR was used as extraction material.

Vertical profile of airborne measured ion composition above the boreal forest L. Beck, J. Duplissy, J. Lampilahti, K. Leino, F. Korhonen, H. Junninen, L.L.J. Quéléver, S. Schobesberger, I. Pullinen, Poutanen, P., T. Petäjä, M. Kulmala

Implications of mycorrhiza, insights from a theoretical model Frank Berninger, Xuan Zhou, Kajar Köster, Heidi Aaltonen, Egle Köster, Jussi Heinonsalo, Marjo Palviainen, Hui Sun, Anatoly Prokushkin, and Jukka Pumpanen

What is the mechanism behind new particle formation in highly polluted urban environments? F. Bianchi, L. Yao, O. Garmash, C. Yan, J. Kontkanen, H. Junninen, S. Buenrostro Mazon, M. Ehn, M. Sipilä, T. Petäjä, M. Kulmala, D.R. Worsnop, L. Wang

New particle formation has been observed in highly polluted cities despite the very high condensational sink.

We conducted intensive measurement at the Fudan University in Shanghai using instrumentation that are the state-of-the-art.

It was found that sulphuric acid with amines are the main responsible for the very high formation rate that it was observed during the measurement period.

Organics, most probably highly oxygenated molecules, are still needed for the growth of the particles above 3 nm.

The effect of relative humidity and chemical composition on the evaporation of secondary organic aerosol particles A. Buchholz, C. Mohr, A. T. Lambe, C. Faiola, E. Kari, S. A. Nizkorodov, A. Pajunoja, A. Ylisirniö, D. R. Worsnop, T. Yli-Juuti, and A. Virtanen

The volatility of the constituents of aerosol particles determines their fate in the atmosphere.

We apply a measurement method which allows us to study the evaporation behavior of SOA particles at room temperature under different humidity conditions and at the same time investigate their chemical composition.

The presence of water in the particles enhances the evaporation either by lowering the viscosity and thus the limitation of the mass transport or by enhancing chemical reactions which lead to smaller, more volatile molecules.

Particle evaporation correlates with average O:C ratio (as proxy for oxidation state/chemical composition) and the evaporation of particles with decreasing volatility with increasing O:C.

FIGAERO-CIMS data suggests that more volatile “monomers” evaporate from the particles and less volatile “dimers” stay behind, thus no big change in O:C ratio is observed during evaporation.

Vertical ion distribuition: effect of forest canopy as an ion sink S. Buenrostro Mazon, H.E. Manninen, J. Kontkanen, D. Wimmer, L. Ahonen, V.-M. Kerminen, M. Kulmala

We evaluate the extent of a boreal forest canopy as an ion sink, by investigating the variations in ion concentrations at below-canopy (4 m) and above-canopy (35 m) heights.

Ion concentrations are obtained from two Neutral Air Ion Spectrometer (NAIS) operating simultaneously, and almost continuously, at ground level (inlet: 4 m height) and above canopy level (35 m tower) since 2014.

We investigate case studies when small ions (<2 nm; cluster band) concentration momentarily decreases (or disappears) in the above-canopy measurements but not at ground level.

Ion Mobility Spectrometer (IMS) coupled with a time of flight mass spectrometer for high-resolution ambient gas and aerosol analysis R. Chellapermal, H. Junninen, T. Petaja, M. Kulmala

IMS can provide additional mobility and cluster level information when coupled with a time-of-flight mass spectrometer.

A 2-month measurement campaign for an IMS with ApiTOF and electrospray ionization (ESI) was conducted in Hyytiala in the spring of 2014, and the results were analysed.

The instrument setup was calibrated using tetra-alkyl-ammonium halides, and a single calibrated theoretical length of the drift region was computed based on utilizing literature reduced mobility values.

Reduced mobilities, K0, were calculated for all compounds, based on maximum IMS response for a given m/z. In addition, assuming spherical particles, the bulk density of clusters was computed, as seen in Figure 1.

Figure 2. Mass-to-charge (m/z) vs reduced mobility K0. Low IMS response signal (<150 arbitrary

units) was filtered out. The density curves for 0.5 – 1.0

g/cm3 are also shown.

Observations of ozone depletion events at smear ii station in a Finnish boreal forest X. Chen, L. L. J. Quéléver, P. L. Fung, J. Kesti, M. P. Rissanen, J. Bäck, P. Keronen, H. Junninen, T. Petäjä, V.-M. Kerminen and M. Kulmala

Observations of surface ozone depletion were often reported with the lack of the vertical profile information on ozone concentrations in the literature.

We analysed a 20-year-long dataset collected at SMEAR II station in Hyytiälä Finland to investigate the variations in the concentrations and vertical profiles of ozone.

We observed that ozone depletion events that lasted for more than 30 min occurred mainly in autumn and winter and we could also find a few cases of long-lasting (>3 hours) ozone depletion events (Table 1).

We concluded that low ozone concentrations episodes were seen typically associated with low temperatures, low wind speeds, high relative humidities and limited intensity of solar radiation.

These conditions are likely to occur upon the formation of a shallow mixing layer. Under such conditions, the enrichment process from residual layer and photochemical production of ozone are prohibited, but ozone continues to be lost through deposition and chemical consumption in the confined mixing layer.

Table 1. The number of ozone depletion events that last for more than 3 hours seen at different heights.

Height [m] 67.2 50.4 33.6 16.8 8.4 4.2

< 10 ppb 148 141 178 202 241 356

< 5 ppb 26 28 29 35 43 63

< 2 ppb 4 5 6 5 6 6

< 1 ppb 1 1 1 1 2 2

Influence of atmospheric conditions on pure biogenic nucleation in the cloud chamber L. Dada1, D. Stolzenburg2, A. Dias3, L. Ahonen1, F. Bianchi1, L. Fischer4, H. Gordon5,6, M. Heinritzi7, K. Lehtipalo1, H. E. Manninen5, C. Rose1, M. Simon7, C. Yan1, M. Xiao8, J. Curtius7, M. Kulmala1, J. Kirkby5.7 And The Cloud Collaboration

New particle formation affect both human health and the global climate.

Pure biogenic nucleation has been reported in some places around the globe and has is expected to have been the only type of nucleation during the pre-industrial era.

We simulated pure biogenic new particle formation in the clean and well-regulated CLOUD chamber under atmospherically relevant conditions.

Semi-long term in-situ cloud measurements during Pallas Cloud Experiments 2012, 2013 and 2015. K. Doulgeris and D.Brus

Semi-long term measurements of in-situ cloud droplet concentrations were carried out during Pallas Cloud Experiments (PaCE) at Pallas-Sodankylä Global Atmosphere Watch (GAW) station, in northern Finland in autumn of 2012, 2013 and 2015.

The main motivation during those campaigns was to investigate aerosol-cloud interactions using in-situ measurements techniques.

In-situ cloud properties are measured by two different cloud probes installed on the roof of the station: a Forward Scattering Spectrometer Probe (FSSP, 3-47 μm, model SPP-100, DMT) and the Cloud, Aerosol and Precipitation Spectrometer (CAPS, DMT), which includes three instruments: the Cloud Imaging Probe (CIP, 12.5 μm-1.55 mm), the Cloud and Aerosol Spectrometer (CAS-DPOL, 0.51-50 μm) with depolarization feature, and the Hotwire Liquid Water Content Sensor (Hotwire LWC, 0 - 3 g/m3).

Each year of the campaign the temperature trends and ranges were similar.

Figure 1.Median volume diameter timelines for PaCE 2012, 2013 and 2015 are shown as they were measured by CAS probe when the measurement site was inside a cloud. The daily averaged data for the temperature versus time for each campaign is also presented.

Decreasing sea ice increases the concentration of potential CCN during winter and decreases during summer E.-M. Duplissy, S. Hakala, V. Sinclair, R. Väänänen, V.-M. Kerminen, T. Petäjä and M. Kulmala

Decreasing Arctic sea ice is likely to change the sources and sinks of aerosols all over the Arctic.

We studied how the time that air parcel spends over consolidated pack ice, open pack ice, open sea and land, effects the aerosol concentrations and size distributions at SMEAR I in eastern Lapland.

The concentrations of potential CCN were found to increase with decreasing sea ice during summer and decrease with decreasing sea ice during winter.

We speculate that the opposite effects during summer and winter might both have a net cooling effect on climate.

Inside a volcanoe plum: new particle formation measured with a flying mass spectrometer J. Duplissy, M. Sahyoun, E. Freney, R. Dupuy, A. Colomb, D. Picard, J. Brito C. Denjean, T. Bourianne, M. Kulmala, M. Riva, H. Juninen, A. Schwarzenboeck, C. Planche, and K. Sellegri

Volcanic emissions are one of the major natural sources of particles in the atmosphere. In 2016, as part of the CLERVOLC/STRAP project, a series of ground based and airborne based (French research aircraft, ATR-42) measurements were performed around Etna and Stromboli volcanos in Italy. A newly develop Xray-APi-tof was on board the aircraft to measure sulfuric acid concentration, and most importantly to monitor new particle formation from a cluster point of view. A total of four flights took place over and around Etna and Stromboli on the 14-16th of June. Evidence of new particle formation was observed within the volcanic plume for both Etna and Stromboli. The new particle formation events coincided with increases in SO2 concentrations. Most importantly, the composition of the molecular clusters involved in the new particle formation will be presented.

Intercomparison of six particle counters – impact on eddy covariance measurment data J.A. Enroth, L. Järvi, P. Aalto, V. Zdímal, T. Petäjä

Particle flux eddy covariance methods are subject to a lot of uncertainties.

We performed a month long particle counter intercomparison campaign in order to compare the different attributes of various types of particle counters.

The faster particle counters which were presumed to perform better fared worse than expected due to smaller sampling volumes, and hence worse counting statistics of particles.

Based on preliminary results, new instrumentation combining speed and a large sample flow could bring considerable improvements in particle flux measurements.

Carbonyl sulfide fluxes over a boreal forest: using COS as a proxy for photosynthesis K-M. Erkkilä, L. Kooijmans, J. Aalto, H. Chen, I. Mammarella, K. Maseyk, M. Pihlatie, U. Seibt, W. Sun, T. Vesala

Carbonyl sulfide (COS) has been suggested to be a useful proxy for gross primary production (GPP) since plants take up COS in a similar way as CO2 via stomata, but there is no back-flux of COS

COS fluxes over a boreal forest were measured with three soil and three branch chambers, and ecosystem scale flux was monitored via eddy covariance (EC) measurements

Our results show negative night-time ecosystem COS flux (indicating uptake) that is explained by incomplete stomatal closure in the leafs as well as soil uptake during night-time

We found that leaf relative uptake (LRU) is exponentially dependent on radiation with low radiation levels, and results in better GPP estimates than using a constant LRU (Fig. 1)

Figure 1. Diurnal cycles of GPPCOS and GPPeco measured with EC technique, when using constant LRU=1.4 (left) and a radiation-dependent LRU (right) in GPPCOS calculation.

Condensation sink in the atmosphere: a simple theoretical model for intermediate Knudsen numbers E. Ezhova, V.-M. Kerminen, K.E.J. Lehtinen and M. Kulmala

We obtain an analytical solution of the condensation equation valid for the range of intermediate Knudsen numbers, significant for atmospheric applications. Assuming an initial lognormal distribution, we further obtain an analytical formula for the condensation sink (CS).

The formula for CS is tested against experimental data in boreal forests (Finland) and a megacity (China). The nucleation mode with a small characteristic diameter 2-3 nm does not contribute significantly to the atmospheric CS even for very high number concentrations (up to 10000 1/cm3), while the accumulation mode with a characteristic diameter 100 nm and larger contributes even if the number concentrations are as low as 100 1/cm3.

We present a simple model describing a coupled dynamics of the condensing vapour and the condensation sink. The model gives reasonable predictions of the CS dynamics during the periods of the aerosol modes' growth by condensation in the atmosphere.

The effect of chamber conditions on product distribution and yield of Highly Oxygenated Molecules in benzene oxidation O. Garmash, M. P. Rissanen, I. Pullinen, J. Wildt, M. Le Breton, M. Priestley, E. Kleist, M. Kulmala, T. F. Mentel and M. Ehn

The most abundant aromatic compounds in the air, including benzene, primarily react with OH and form HOM (Highly Oxygenated Molecules) in the laboratory experiments.

We conducted a chamber study at Forschungszentrum Jülich, Germany in which we have varied different parameters, such as VOC/O3/NOx concentration as well as light intensity to sample an array of environmental conditions.

We have observed a high molar yield of HOM, which increased as a function of OH, suggesting that multiple oxidation steps are important in the formation of some HOM compounds in aromatic oxidation.

The distribution of the HOM products was different in the chamber study as compared to previous flow tube measurements and the formation of highly oxygenated organic nitrogen-containing compounds were observed upon addition of NOx.

Understanding on how the product composition and the yield of HOM change as a function of OH and NOx is crucial for estimating the significance of aromatic compounds in urban particle and secondary organic aerosol (SOA) formation as well as for identifying the HOM compounds in the ambient urban air.

Atmospheric ice and dust: from single particles to global radiation P. Haapanala, H. Lindqvist, S. Merikallio, and E. Riskilä

Recent computational and methodological advances in light scattering and radiative transfer modelling have made it possible to use more morphologically faithful particle shape models in atmospheric radiation research, and the three dissertations summarised here demonstrate these advances all the way from morpholocigal modelling to light scattering computations and to radiative transfer modelling.

It seems that assumption of spherical shape in calculating optical properties of dust particles (Fig. 1) is not a considerable error source for global aerosol-climate models, but can be for remote sensing applications.

We have discovered new insight into the connections between ice crystal morphology (Fig 1), ice cloud microphysics and solar radiative transfer.

Fig 1. Examples of the various shapes of atmospheric a) ice crystals, and b) mineral dust particle, We wish to thank Olga Munoz and Konrad Kandler for kindly providing us the images of the particles.

Methane fluxes from tree stems in a nutrient rich forestry drained peatland in southern finland I. Haikarainen, A. Putkinen, P. Pyykkö, M. Korkiakoski, E. Halmeenmäki, A. Lohila, M. Pihlatie

Recent studies have demonstrated that trees are capable of emitting methane (CH4) from their stems and shoots possibly by transporting anaerobically produced CH4 from deeper soil layers to the atmosphere.

We have measured tree stem CH4 exchange of three common boreal tree species at Lettosuo, a forestry drained, nutrient rich peatland forest during 7 June – 17 October 2016 in two different plots: a control plot and a partially harvested plot where all the Scots pine (Pinus sylvestris) trees (75% of the tree biomass) were removed to raise the water table level (WTL).

The WTL was closer to soil surface at the partially harvested plot compared to the WTL on the control plot and the CH4 emissions were generally higher and more dominant at the partially harvested plot compared to the control plot (Figure 1).

The difference in the tree CH4 fluxes between the control and partially harvested plots suggests that the WTL could be a major regulator of tree CH4 emissions on forestry drained peatlands, supporting our hypothesis that the CH4 emitted by the stem originates from the soil.

Figure 1. Box & whiskers plots of tree stem CH4 fluxes at partially harvested (top panel) and control (bottom panel) plots at Lettosuo in summer 2016, southern Finland. The top and the bottom of the boxes mark 25% and 75% percentiles and the whiskers show the range of entire flux data.

New particle formation at a rural background site in western saudi arabia S. Hakala, P. Paasonen, V. Vakkari, H. Lihavainen, A. Hyvärinen, K. Neitola, J. Kontkanen, T. Hussein, Kulmala, and M. A. Alghamdi

Molecular dynamics simulations and isothermal homogeneous nucleation R. Halonen, V. Tikkanen, E. Zapadinsky and H. Vehkamäki

The isothermal nucleation rates obtained through Monte Carlo (MC) simulations of Lennard-Jones argon have been compared to ones calculated with the molecular dynamics (MD) simulations.

We observe good agreement only when carrier gas is used as a thermostat in MD simulations and the nonisothermal nucleation theory is used.

Other thermostatting methods are less successful in thermalizing the nucleating system and the “nonisothermality” depends on the temperature and the vapor density.

Our results indicate that the practice of thermostats in MD simulations should be carefully considered, but also the nonisothermal nucleation theory and the standard kinetic treatment should be carefully reexamined.

Figure 1. Difference between the nucleation rates obtained by the MC and the MD simulations as a function of the monomer density. The arrows indicate cases where only the upper limit for nucleation rate was derived. Crosses mark the comparison with the nonisothermal nucleation theory when using carrier gas.

Aerosol chemical composition in- and out-of- clouds in Finland L.Q. Hao, O. Välisänen, A. Ylisirniö, Y.H. Wang, K. E. J. Lehtinen, D. R. Worsnop, And A. Virtanen

Inorganinc nitrate dominated the nitrate aerosol components in cloud periods and organic nitate contribute about half to nirate in cloud-free periods.

Aersol were more neutralized during cloud periods than cloud-free periods.

A better correlation of secondary organic aerosol to sulfate during cloud period than cloud-free periods.

Impact of aerosol acidity on organic nitrates formed from α-pinene ozonolysis L. Heikkinen, M. Riva, O. Peräkylä, S. Schallhart, J. Enroth, O. Garmash, M. Äijälä, T. Petäjä, D. Worsnop, and M. Ehn

The impact of aerosol acidity on organic nitrates formed from α-pinene ozonolysis was investigated in a Teflon chamber using a variety of mass spectrometers enabling us to capture the whole SOA formation process from VOCs to aerosol particles.

Aerosol acidity enhances SOA and the particulate organic nitrate (pON) formation. Aerosol liquid water dilutes the acidity which likely slows down the heterogeneous processes. Organic nitrates might undergo further particle phase processes especially in acidic particles.

Greenhouse gas fluxes on adjacent wetland, lake and forest ecosystems within a subarctic catchment L. Heiskanen, M. Aurela, J.P. Tuovinen, T. Virtanen, S. Juutinen, A. Räsänen, T. Penttilä, T. Laurila

• Eddy covariance measurements of greenhouse gas fluxes are conducted on adjacent wetland, lake and forest sites to provide continuous data from the main ecosystems of the area enabling the integration of greenhouse gas fluxes over the whole catchment.

• Flux chamber measurements conducted at the wetland and lake sites combined with the detailed land cover and vegetation mapping based on satellite data and field measurements add more detail to the areally averaged data obtained from the eddy covariance measurements.

• Using these data, the annual ecosystem-level greenhouse gas balances will be determined and upscaled to a catchment scale and further to a regional scale.

Ambient air BVOC mixing ratios are highly dependent on temperature H. Hellén, A.P. Parplan, T. Tykkä, H. Hakola

BVOC mixing ratios (isoprene, monoterpenes, sesquiterpenes) were measured at SMEAR II site in 2011, 2015 and 2016 with three different in situ gas chromatograph – mass spectrometers.

Monthly and daily means of mono- and sesquiterpene mixing ratios were exponentially dependent on temperature with high correlation.

Even though isoprene emissions are known to be both light and temperature dependent, higher dependence of daily mean mixing ratios was found only for temperature (R2=0.84) than for light and temperature activity factor (R2=0.74).

Figure 1. Correlation of temperature with monthly mean MT mixing ratios measured in 2011, 2015 and 2016 at SMEAR II site in Hyytiälä.

Concentrations of volatile organic amines in ambient air of boreal M. Hemmilä, H. Hellén, A. Virkkula, U. Makkonen, A.P. Praplan, J. Kontkanen, M. Kulmala, H. Hakola

Amine measurements were performed at SMEAR II -station in Hyytiälä from March to December 2015.

The amines turned out to be a heterogeneous group of compounds; different amines are likely to have different sources.

Particle phase monomethylamine concentrations were high in early spring, but decreased when days got warmer.

Dimethylamine concentrations had weak positive correlation with cluster-mode particles and correlation had some dependence on the humidity and temperature of soil and air.

Towards monitoring of icing conditions with operational ceilometer network and evaluation of icing forecast model A. Hirsikko, M. Komppula, A. Leskinen, K. Hämäläinen, S. Niemelä, and E.J. O’connor

Super-cooled liquid water containing clouds are frequent over Finland. Such clouds have significant potential for causing icing and producing precipitation (including freezing rain).

In this study we have investigated potential of a ceilometer to pinpoint icing conditions. We have developed a classification scheme for icing potential of hydrometeors observed in ceilometer backscatter profiles.

Comparison with in-situ sensor observations indicates that the two sensor types observe icing conditions almost as often, simultaneously 64 -85 % of time periods during study period when ceilometer had indicated icing condition. Inclusion of precipitation in classification increases number of simultaneous observations between the two observation scales.

Wet deposition scheme in ECHAM-HAMMOZ climate model T.E. Holopainen, H. Kokkola, T. Kühn

Global aerosol-climate models usually underpredict aerosol transport into the arctic regions, which may be attributed to how the models simulate wet deposition processes.

We extracted the wet deposition module from the aerosol-climate model ECHAM-HAMMOZ into a boxmodel setting and built the supporting modules around it.

The boxmodel calculates the wet deposition tendencies of the aerosol tracers very well, which is a very good starting point for further refinement of the wet deposition scheme in ECHAM-HAMMOZ.

A whole tree level model of stomatal conductance maximizing tree metabolic rate T. Hölttä, A. Lintunen, T. Chan, A. Mäkelä, and E. Nikinmaa

We demonstrate using a numerical model that stomatal functioning can be understood from the viewpoint of maximizing the simultaneous photosynthetic production, phloem transport, and sink sugar utilization rate.

Maximizing the photosynthetic production rate using a numerical steady-state model leads to stomatal behaviour that is able to reproduce the well-known trends of stomatal behaviour in response to e.g. light, VPD, ambient CO2 concentration, soil water status, sink strength, and xylem and phloem hydraulic conductance.

Our modeling results also demonstrate how the “marginal cost of water” in the unified stomatal conductance model and the optimal stomatal model could be related to plant structural and physiological traits, most importantly, the soil-to-leaf hydraulic conductance and soil moisture.

New calibration method for the condensation particle counters E. Häkkinen, J. Kangasluoma, F. Korhonen, P. Aalto, T. Petäjä

Particles with different charge and size combinations can have the same electrical mobility and cause errors in number concentration and size calibrations.

In this study, a calibration device similar to single-charged aerosol reference (SCAR) was built and its performance was assessed. The device can be used to calibrate condensation particle counters without error caused by multiply charged particles.

The calibration device generated narrow particle size distribution and the fraction of doubly charged particles was only 0.043 %.

Figure 1. Primary size distribution, the distribution through the DMA and charging probabilities for negative elementary charges 1 and 2. Comparing statistical dimension reduction techniques in the analysis of multivariate atmospheric data S. Isokääntä, E. Kari, C. Faiola, A. Buchholz and S. Mikkonen

Statistical dimension reduction techniques are applied to multivariate data to compress the information from a large number of correlated variables to a small number of latent variables.

In preliminary studies, we applied different dimension reduction techniques to Scots pine emission measurements that were monitored by Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS).

Three factors were identified; plant stress, diurnal cycle and background. All used methods were able to construct identifiable plant stress factor, however, only factor analysis distinguished background from other factors.

Figure 1. Factor/component scores created from Scots pine emissions. Shaded area indicates the active feeding period of the pine weevils. Effect of air temperature on the urban energy and hydrological cycle in cold climate regions L. Järvi, C.S.B. Grimmond, J.P. Mcfadden, A. Christen, I.B. Strachan, M. Taka, L. Warsta, and M. Heimann

In our study we examined the joint effect of winter time temperatures and degree or urbanisation on the hydrological cycle in cold climate cities. The results show how inter-year variability of wintertime temperature modifies the effect of snow and with increasing temperatures, these cities can be pushed towards very different partitioning between runoff and evapotranspiration. We derive the dependency of wintertime runoff on this warming effect in combination with the effect of urban densification.

The effects of elevated ground surface ozone on the growth of physiology of Japanese larch and its hybrid seedlings D. Kam

The ground surface ozone (O3) is a phototoxic air pollutant, which inhibits the physiological activities of plants, and excessive nitrogen (N) deposition may influence the imbalanced development of each organ in plant.

In order to investigate the effect of the different O3 concentration on the seedlings of Japanese larch (JL) and its hybrid (HL), seedlings were exposed to four O3 levels in open-top chambers.

For the interactive effect of elevated O3 concentration and N deposition, seedlings of JL and HL were exposed to elevated O3 and applied with NH4NO3

The HL seedlings were more sensitive to O3 and/or excessive N deposition.

A new “1 nm” high flow dmps based on half-mini dma and a11, and sub-10 nm particle observations in boreal forest in hyytiälä, finland J. Kangasluoma, L. Ahonen, T. Laurila, J. Enroth, F. Korhonen, P. Aalto, M. Kulmala, T. Petäjä, and M. Attoui

Sampling plays a crucial role due to high diffusion losses. The sampling lines should be always experimentally characterized

DMPS systems operated with DEG based CPC cannot be used for sub-2(-3) nm particle concentration measurements in systems where those particles are organic species.

The higher the number of counted particles, the less counting uncertainties. This calls for high flow CPCs especially if the DMPS system is used in low particle concentration environments.

The largest sources of inaccuracy are the lowest detectable particle size and charging probabilities

Sub-10 nm particle concentrations are possibly underestimated in Hyytiälä on average by a factor of 3 in the past measurements

The effect of gasoline car exhaust on photochemistry of alpha-pinene E. Kari, A. Ylisirniö, S. Isokääntä, P. Yli-Pirilä, A. Leskinen, S. Mikkonen, L. Hao, A. Virtanen

One of the first studies where a real anthropogenic emission source was used to study anthropogenic-biogenic interactions in environmental chamber.

Gasoline car exhaust did not have a significant effect on the formed SOA mass from photooxidation of α-pinene.

Preliminary results from factor analysis suggested that there are possible interactions between gasoline car exhaust and α-pinene.

10th year of cloud condensation nuclei measurements at SMEARII H. Keskinen1,2, P. Aalto1, J. Levula1,2, H. Laakso1,2, M. Loponen1,2, R. Pilkottu1,2, S. Rantanen1,2, M. Kulmala1 and T. Petäjä

We present here the current CCNc measurement unit at SMEARII. Actually, we are celebrating these measurements anniversary at this year as they had been ran from the year 2007. We have here an excellent base for the dataset of the polydisperse and monodisperse measurements in long run. These measurements have had already important role when we have estimated the atmospheric nanoparticles CCN impacts in topical in worldwide networks such as EUCAARI and ACTRIS.

Marine emissions of primary organic aerosol using two different parametrisations in a chemical transport model J.-P. Keskinen, R. Makkonen, S.M. Burrows, H. Kokkola, N.L. Prisle

The breaking of ocean waves creates bubbles, which release sea salt and organic aerosol to the air as they burst.

We have implemented organic sea spray aerosol emissions to the global chemical transport model TM5 using two different parametrisations.

Our simulations show a clear increase in the emissions of primary organic aerosols, especially the Southern Ocean.

Effect of source and precipitation on long-range transported aerosol particles in Maldives J. Kesti, J. Backman, E. Asmi, E. J. O’Connor, Ö. Gustafsson, K. Budhavant

A significant removal process of aerosols from the atmosphere is wet deposition, but the process still has major uncertainties in atmospheric models.

We analyzed aerosol particle data measured in Maldives to investigate the effect of source and precipitation on particle size distributions.

We used k-means clustering for aerosol particle data measured with a Scanning Mobility Particle Sizer (SMPS) and calculated back trajectories for different air masses using the HYSPLIT 4.9 model.

The results imply that the shapes of different clusters depend on the source and the precipitation intensity experienced en route to the site.

Figure 1. A histogram of aerosol particle size distributions measured with SMPS in Maldives. Stdudying aerosol radiation feedback loop based on satelite data M. Khansari, A. Nikandrova, L. Dada, V.M Kerminen, P. Paasonen AND M. Kulmala

Aerosols can influence the amount of radiation reaching the surface due to absorption and scattering. This may produce a feedback mechanism which can diminish or amplify temperature.

We are analyzing aerosol radiation feedback loop (Fig 1) based on satellite data. In this study ground based data is used for validation of our results from satellite data.

Figure 1. The aerosol radiation feedback loop. Where GPP is gross primary production, SOA is secondary organic aerosols, CS is the condensation sink and R is the ratio between diffuse radiation (Rd) and global radiation (Rg).

Impact of haze on urban energy and water balance in Beijing T.V. Kokkonen, S. Murto, C.S.B. Grimmond, H.Z. Liu, A.-M. Sundström, L. Järvi

Most of the urban energy and water balance modelling has focused to mid-latitude western countries, whereas relatively limited amount of studies have been made in Asian newly industrialized countries such as China. In these areas industrialization has brought severe air quality problems. We studied how the haze affects the local urban energy and water balance and how well an urban energy and water balance model developed based on observations in Europe and Northern America performs in Beijing.

The Surface Urban Energy and Water Balance Scheme (SUEWS) simulates the latent heat flux (QE) well in Beijing, whereas there is a systematic overestimation of sensible heat flux (QH).

Cookstove emissions and ice nucleation: an experimental study K. Korhonen, T.B. Kristensen, R. Lindgren, R.L. Carvalho, C. Boman, B. Svenningsson, J. Falk, J. Pagels, M.Komppula, K.E.J. Lehtinen and A.Virtanen

• Ice nucleating capabilities of biomass-fired cookstove emissions were experimented using a commercial ice nuclei counter SPIN.

• Studied cookstoves included two appliances that are commonly used in sub-Saharan Africa for daily cooking, and two advanced gasifier stoves.

• Fresh cookstove emissions were observed to have a low ice nucleating potential in general. • Heterogeneous ice nucleation was observed in cases when cookstove performance was intentionally

deteriorated for increased soot production. This indicates that large soot particles are an essential component for ice nucleating ability of cookstove emissions.

Eddy covariance measurements of carbon dioxide and energy fluxes after clearcutting in a drained peatland forest M. Korkiakoski, J.-P. Tuovinen, J. Rainne, T. Laurila, A. Lohila We measured CO2 fluxes with the eddy covariance technique in a drained peatland forest after clearcutting. The site turned from being CO2 neutral into a large CO2 sink after clearcutting, emitting almost 3 kg CO2 m-2 yr-1, mainly due to an 80% decrease in GPP. Ecosystem respiration decreased by 25% after clearcutting due to a rise in the water table level, which decreased the soil decomposition rate more than the increased temperatures enhanced soil respiration. Bowen ratio decreased from 2.4 in May to 0.8 in August, which was caused by the decrease in sensible heat flux as the developing grass and moss layer increased albedo.

Figure 1. Time series of daily mean net ecosystem exchange (NEE, top panel), gross primary production (GPP, middle panel) and ecosystem respiration (Reco, bottom panel) measured at the clearcut from April 2016 to August 2017.

Grazing by reindeer in northern boreal forests – how it is affecting greenhouse gas emissions from forest floor K. Köster, E. Köster, F. Berninger, J. Heinonsalo, J. Pumpanen.

Reindeer grazing shifted the composition of the ground vegetation from being dominated by lichens to being dominated by mosses.

The greenhouse gas emissions differed significantly between grazed and non-grazed areas and the CO2, CH4 and N2O fluxes were depended on the changes in the vegetation composition caused by reindeer.

Soil was always found to be a source of CO2, and soil CO2 emissions were significantly smaller in non-grazed areas compared to grazed areas.

Soils were CH4 sinks through entire measurement period, and grazed areas consumed more CH4 compared to non-grazed areas.

The N2O emissions were significantly affected by moss biomass, while non-grazed areas with lower moss biomass and soil temperature were a small sink of N2O.

Greenhouse gas fluxes from a fire chronosequence in northern boreal forests of Canada E. Köster, K. Köster, F. Berninger, H. Aaltonen, X. Zhou, J. Pumpanen.

The depth of the active layer on top of permafrost was increasing rapidly after the fire and the increase in the active layer thickness resulted in higher GHG emissions.

Fire is causing long-lasting changes of GHG emissions and the only factor affecting studied GHG fluxes was the time since last forest fire.

Soil CO2 efflux decreased shortly after the fire.

Subarctic boreal forests acted as sinks of CH4 in our study, but changes in CH4 fluxes lasted for a short period of time.

A slight decrease in N2O emission could be observed in comparison of different fire age classes.

Removal of semi-volatile compounds from the atmosphere I. Kudzotsa, H. Kokkola, J. Tonttila, T. Raatikainen, S. Romakkaniemi

In this study we use a state-of-the-art LES model UCLALES-SALSA comprising an interactive aerosol-cloud scheme SALSA, which tracks aerosols through all processes that modify aerosol distributions to asses how semi-volatile compounds interact with clouds and are removed from the atmosphere by wet processes.

The figure below shows the time evolution of the total gas-phase and particle-phase concentrations of semi-volatile gases in a closed system simulation. It is apparent that the gas-phase concentrations are almost depleted within half an hour into the simulation

Efficacy of black carbon mitigation in slowing arctic warming T. Kühn, H. Kokkola, K. Kupianen, K. Kulovesi, Yamineva, Y., Khan, S., Karvosenoja, N., Savolahti, M., Paunu, V-V., Klimont, Z., and K.E.J. Lehtinen

Arctic mean surface temperatures increase at a much faster rate than global averages and mitigation of short-lived climate pollutants (SLCP) has been suggested as a short-term measure to slow Arctic warming. Here we use the aerosol-climate model ECHAM-HAMMOZ to assess the impact that emission reductions of black carbon (BC) in different regions of the globe have on the Arctic climate. The general result is that sources close to the Arctic have the largest relative effect. However, as emissions in and close to the Arctic region are already low, the full potential of BC emission reductions can only be reached if the stronger regions at lower latitudes are targeted as well.

The carbon dynamics of boreal dwarf shrubs differ from those of Scots pine seedlings L. Kulmala, M.D.R. Dominguez Carrasco, J. Heinonsalo

It is not known how much of the primary production of ground vegetation is shortly released as CO2 and how much is bound to organic matter.

We studied C dynamics in detail using plants of similar size in a in a controlled microcosm study.

We showed that root respiration of the evergreen ericoid dwarf shrubs was sensitive to the aboveground light conditions as belowground respiration higher under light compared with dark conditions (Fig. 1).

Such light-related differences were not observed for Scots pine.

Figure 1. The ratio between root respiration in darkness and in light conditions in the measured individuals of different species

High-resolution dispersion and air quality modelling in urban areas M. Kurppa, A. Hellsten, M. Auvinen and L. Järvi

Large-eddy simulation (LES) can be applied to study the transport of air pollutants in very complex environments. A sectional aerosol module SALSA has successfully been coupled with a LES model PALM to enable high- resolution air quality modelling including aerosol dynamic processes of condensation, evaporation, coagulation, nucleation and dry deposition on vegetation. The coupled model will be evaluated against data from measurement campaigns in different urban locations

Trends of atmospheric mercury at a sub-arctic site Pallas in Finland K. Kyllönen, I. Wängberg, P. Anttila, H. Hakola

Atmospheric total gaseous mercury has been measured for twenty years at a sub-arctic site Pallas in Northern Finland in co-operation of FMI and IVL.

The results show a concentration at the global background level of 1.4-1.5 ng m-3 and a seasonal trend with higher values in the winter due to energy production.

During springtime, unusually low mercury concentrations are occasionally observed when atmospheric mercury depletion events have occurred in the Arctic and the depleted air masses reach the Pallas site.

The trend analysis showed that there has been absolutely no change in the mercury concentration in the measurement period, nor in the last eight years when an automatic instrument was employed for the measurements (Fig. 1) in spite of significant emission reductions in Europe.

Figure 1. Atmospheric measured and modelled concentrations (monthly values) with annual trends of total gaseous mercury at Pallas in 1996-2014. No trend is detected.

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Sub-10 nm aerosol particle layers observe aloft using an instrumented airplane J. Lampilahti , K. Leino, R. Väänänen, A. Manninen, P. Poutanen, S. Buenrostro Mazon, H. E. Manninen, T. Petäjä and M. Kulmala

We measured aerosol particles and meteorological variables using an aircraft and observed elevated sub-10 nm aerosol particle layers that were often associated with a capping inversion.

Nano-cava project – formation of clusters from atmospheric vapours K. Lehtipalo, U. Baltensperger, and M. Kulmala

Airborne observations of aerosol particles in Lapland K. Leino, J. Lampilahti, P. Poutanen, P. Hietala, A. Manninen, A. Nikandrova, M. Peltova, P.P. Aalto, F. Korhonen, E. Sihvonen, J. Kangasluoma, L. Ahonen, T. Petäjä and M. Kulmala

Atmospheric new particle formation has observed to occur all over the world, under different environments, and also vertically from the ground level, inside the planetary boundary layer, up to the free troposphere.

In August 2017 we conducted the research flight campaign in Finnish Lapland using a small Cessna 172 aircraft as a platform for the aerosol instrumentation. Total particle concentrations with 1.5 and 3 nm cut-off sizes, particle size distribution, CO2- and H2O –gas concentrations and meteorological parameters were measured during 20 measurement flights over Eastern and Western part of Finnish Lapland.

Around the operated area we have supporting observations from the ground-based measurement stations in Värriö and Pallas.

By combining the ground-based observations, airborne observations from ground level up to 3500 meters (a.m.s.l.) and HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) air-mass trajectory analysis, we are able to study vertical and horizontal differences and similarities in aerosol populations.

Applying causal models to small-scale wood combustion data V. Leinonen, O. Sippula, P. Tiitta, A. Leskinen, M. Kortelainen, J. Karvanen, A. Virtanen, S. Mikkonen

The data for our study were collected in chamber experiments, conducted in ILMARI environmental chamber at the University of Eastern Finland. In ILMARI environment, it is possible to investigate the aging of combustion emission in atmospheric-like conditions in a controlled environment.

By using causal model and causal calculus, it is possible to do statistical inference how variables relate to each other and compute how much changing of one variable affects to other variables. Despite the fact that causal models are powerful tools for complex atmospheric measurement data, they have not been used before with these kind of data.

The goal of this study is to investigate how the aging of combustion emissions in atmospheric conditions affect to adverse health and climatological effects of aerosols.

Effect of temperature on evaporation of secondary organic aerosol from photooxidation and ozonolysis of α-pinene Z. Li, A. Buchholz, O.-P. Tikkanen, E. Kari, L. Hao, T. Yli-Juuti, and A. Virtanen

Volatility of secondary organic aerosol (SOA) constituents, governs their partitioning between gas phase and particulate phase.

Two crucial processes affecting particle evaporation, molecular diffusion and oligomer decomposition, are temperature-dependent, and therefore investigations on SOA evaporation at various temperatures are highly needed.

We conducted a series of particle evaporation experiments with α-pinene SOA generated from photooxidation and from ozonolysis, under varied relative humidity (RH) both at 10 °C and at 20 °C

Difference in temperature and variation in SOA chemical composition resulted in the distinctive SOA evaporation behaviour under different RH.

Characterization of aerosl optical properties in western saudi-arabia using postive matrix factorization H. Lihavainen, M. A. Alghamdi, A. Hyvärinen, T. Hussein, K. Neitola, M. Khoder, A. S. Abdelmaksoud, H. Al-Jeelani, I. I. Shabbaj, and F. M. Almehmadi

We utilized positive matrix factorization to characterize mass absorption and scattering coefficients from different sources.

We studied the black carbon mixing state in two sites in Northern India, urban and rural sites. These findings indicate that particles at both sites have similar local and regional emission sources, but aerosols are also transported from the main source regions (IGP) to the less polluted regions (Himalayan foothills).

Belowground hydraulic conductance in mature Scots pine trees A. Lintunen, T. Paljakka, Y. Salmon and T. Hölttä

Our aims were to analyze how soil temperature and soil water content is linked to belowground hydraulic conductance (kbg), and to analyze how stomatal conductance (gs) is affected by kbg.

kbg was calculated based on continuous sap flow and xylem diameter measurements in field conditions.

Soil temperature was shown to be the limiting factor for belowground hydraulic conductance in the studied boreal stand especially in spring, although kbg increased also with increasing soil water content if soil temperature was high enough.

kbg was strongly linked to gs, especially when soil was cold.

Modeling of canopy scale solar-induced chlorophyll fluorescence in a heterogeneous boreal forest Weiwei Liu, Jon Atherton, Matti Mõttus, Alasdair MacArthur, Hakala Teemu, Kadmiel Maseyk, Iain Robinson, Eija Honkavaara, Albert Porcar-Castell

Most of the current studies on solar-induced chlorophyll fluorescence (SIF) radiative transfer in plant canopies are based on the assumption of a homogeneous canopy.

We present a canopy SIF modeling study using the 3-D radiative transfer model DART recently have been developed capable of simulation of fluorescence signal in explicit 3-D forest canopies.

A semi-realistic boreal forest tree was created by the Blender software, which is a free and open source 3-D creation software.

The SIF image of simulation scene and full-spectrum canopy-reflected radiance and SIF was simulated based on the integration of DART and Blender.

Figure 1. Modeling the SIF image (c) at 740 nm ( 2nit : / / /U W m m srµ ) of simulation scene (b) using DART model based on a semi-realistic boreal forest tree (a) created by the Blender software. The Seasonal variation of the multiple scattering correction factor at the SMEAR II station K. Luoma, A. Virkkula, P. P. Aalto, T. Petäjä, M. Kulmala

The absorption coefficient of aerosol particles properties has been measured at the SMEAR II with a seven wavelength Aethalometer and with a Multi-Angle Absorption Photometer (MAAP) during 2013 - 2016. The multiple scattering correction factor (Cref) was defined for the Aethalometer by comparing the absorption measurements to the absorption measured by the MAAP. The Cref has a seasonal variation even though it should depend only on the filter. The Cref was higher than the median during the summer and lower than the median during winter. The Cref seemed to depend on the relative humidity of the air.

Seamless/ online integrated meteorology-chemistry-aerosols modelling at multi-scales for PEEX domain A. Mahura, R. Nuterman, A. Baklanov, B. Amstrup, R. Makkonen, T. Petäjä, M. Kulmala, S. Zilitinkevich

The Enviro-HIRLAM, being as one the PEEX-Modelling-Platform models, is planned to be further continued developed at UHEL (CSC project – “Enviro-HIRLAM seamless modelling of meteorology-chemistry-aerosols interactions and feedbacks on multi-scales”) and applied for different research tasks according to the PEEX Science Plan (PEEX, 2015) and research proposals.

The emphasis is on evaluation and testing of the seamless/ online integrated approach for in-depth sensitivity analyses of mechanisms, relationships, feedbacks, interactions, etc. between chemistry-aerosols and meteorology.

The model applicability is shown on examples of the FP7 EU MEGAPOLI & MarcoPolo and NordForsk CarboNord projects.

Nucleation and aerosol size distribution in ec-earth3 R. Makkonen, R. Schrödner, T. Bergman and T. van Noije

Up to 50% of global cloud condensation nuclei can form through atmospheric nucleation, hence it is a crucial process in global aerosol-climate models. We have implemented parallel nucleation schemes in Earth System Model EC-Earth3, including binary sulfuric acid–water nucleation and organic boundary layer nucleation parameterizations.

The implemented boundary layer nucleation mechanisms are based on both sulfuric acid and organic vapours - both are needed for nucleation. Without marine organic precursor sources, nucleation rate has a strong sea-land contrast (Figure 1).

The implemented nucleation mechanisms will be included in Coupled Model Intercomparison Project Phase 6 (CMIP6) experiments for IPCC AR6.

Figure 1. Increase in surface-level N10 (cm-3) due to nucleation.

Performance of MARGA instrument in ammonia measurements U. Makkonen, A. Virkkula, M. Twigg and H. Hakola

.

The MARGA online ion chromatograph was taken to the ammonia field inter-comparison at an intensively managed grassland in South-Eastern Scotland.

MARGA proved to work well with small concentrations

During the high ammonia concentrations about 3-8 % of ammonia was not diffused in the denuder but passed through to the SJAC instead, and was measured as ammonium.

The capacity of the MARGA denuder may be overloaded at high concentrations and the all the gas molecules are not able to diffuse in the denuder and are therefore considered as their aerosol counter-ion.

Using Gaussian mixture modeling in target classification with Doppler wind lidar A.J. Manninen and E.J. O’Connor

Combination of relative variance of lidar signal-to-noise ratio and vertical velocity can be used in distinguishing between aerosols, clouds, and precipitation.

Gaussian mixture modeling enables probability based target classification with Doppler wind lidar.

Robust target classification is essential in lidar applications.

Aerosol Particles (0.3-10 μm) inside a Workshop Area-Emission Rate and Deposited Dose A.Maragkidou, O. Jaghbeir, K. Hämeri, T. Hussein

Investigation of the effect of some indoor activities (such as having lecture, smoking, making coffee, iron welding, scrubbing and sorting/drilling) occurring inside the workshop area on the particle number (PM) and mass (PM) concentration of submicron (0.3-1 μm) and micron (1-10 μm) particles .

Assessment of workers’/students’ exposure to large particles (PM10) inside a workshop area of an educational building (Department of Physics, the University of Jordan) and estimation of the emission and loss rate of aerosol particles using a simple indoor aerosol model.

During the weekend, PN0.3-10 (PM0.3-10) varied from 12.86 to 64.64 cm-3 (1.68-13.58 μg m-3), while during the weekdays PN0.3-10 (PM0.3-10) ranged from 23.13-4162.44 cm-3 (1.15- 596.60 μg m-3).

During weekdays, the highest mean and median PN1-10 (PM1-10) and PN0.3-1 (PM0.3-1) concentrations were observed during the operation of the welding machine, followed by the activity of iron welding without the simultaneous use of the exhaust fan and also with the running of the exhaust fan afterwards, whereas the maxima PN1-10 (PM1-10) and PN0.3-1 (PM0.3-1) concentrations were detected when iron welding took place, and later the operation of the exhaust fan and the activity of iron sorting/drilling occurred.

The head region received the largest fraction of the deposited dose during two events for which it was assumed the workers/students were standing/resting, while during two events for which it was considered the workers/students were performing light exercise the alveolar region received the majority of the deposited dose for light exercise.

Ecosystem photosynthetic production and the length of vegetation active period during this century T. Markkanen, L. Backman, M. Kämäräinen, A. Leppänen, J. Mäkelä, J. Susiluoto, T. Thum, J. Liski, T. Aalto

Various climate change indicators for Finland were extracted from simulations performed with a ecosystem model JSBACH that was calibrated for the region. The model was forced with prescribed climate through years 1981 to 2099 adopted from nine CMIP5 climate scenarios including both rcps 4.5 and 8.5.

The start dates of photosynthetically active season showed significant decreasing trends (p<0.0001) in all the simulations throughout the 120 years and the end dates of the season increased significantly everywhere in all but one rcp 4.5 simulation where in some areas the trend was not significant.

Figure 1. An example of the simulated daily gross primary production timeseries (green) through years

1981 to 2099 averaged over a southern Finnish vegetation zone. Yearly start and end dates of

photosynthetically active season are indicated with red and blue dots, respectively. Forcing

meteorological data was adopted from a CanESM2 RCP4.5 run.

Soil phosphorus concentration determines ground vegetation dynamics in a subarctic forest ecosystem L. Matkala, J. Isotalo, U. Makkonen, M. Salemaa and J. Bäck

Phosphorus is an important nutrient for plant growth and also boreal forests can suffer from P deficit.

We studied the effects of high soil P concentration on ground vegetation composition and needle and leaf concentrations in a subarctic forest site with naturally varying soil P concentrations.

The needle P concentrations were not affected by high soil P concentration. High soil P in the organic layer favors the growth of graminoids and forbs in subarctic forest.

Anthropogenic black carbon emissions in iceland: concentrations observed in snow and glacier ice in southern iceland O. Meinander, P. Dagsson-Waldhauserova, M. Aurela, K. Kupiainen, O. Arnalds, A. Virkkula, J. Svensson, H. Lihavainen, M. Gritsevich, A.N. Arslan, G. de Leeuw, J. Paatero, A. Laaksonen

In the Arctic region, the albedo feedback mechanism, e.g., due to deposited black carbon (BC), can accelerate snow and ice melt. BC in air and snow in the background areas has been investigated and assessed largely in the other Nordic countries, except in Iceland. Our research question is whether BC is a significant contributor to snow and glacier melting in Iceland.

We sampled snow and glacier ice in southern Iceland in March 2016 and March 2017, for the analysis of their BC concentrations at the Finnish Meteorological Institute using Thermal/Optical Carbon Aerosol Analyzer (OC/EC). We also used the official CLRTAP national BC emission inventory of Iceland (available at http://cdr.eionet.europa.eu) to understand and explain the results.

On the basis of our observations, the radiative forcing effects of organic carbon and dust on snow and ice in Iceland can be bigger than effects of BC, and need to be assessed more in detail. Instead of BC, we suggest that one of the main Icelandic glacier melting triggers (in addition to Arctic warming) can be organic material and volcanic dust and ash (i.e., so-called high latitude dust, HLD) on the glacier surface.

Year EC in glacier [ppb] EC closer roads [ppb] 2016 2017

< 12 < 4

< 203 (old snow) < 70 (new snow)

Table 1. Summary of black carbon (elemental carbon, EC) concentrations [ppb] observed in snow and glacier ice samples in 2016 and 2017 in Iceland.

Does Increasing Temperature Increase Carbonaceous Aerosol Direct Radiative Effect over Forests? T. Mielonen, A. Hienola, T. Kühn, J. Merikanto, A. Lipponen, T. Bergman, H. Korhonen, P. Kolmonen, L. Sogacheva, D. Ghent, A. Arola, G.F.R de Leeuw, H. Kokkola

This is the first systematic investigation of aerosol optical depth (AOD) dependence on temperature over forested regions in order to illuminate potential future feedback mechanisms due to interactions between climate change, biogenic emissions and aerosol radiative effects.

Over the studied forests, AOD exhibits temperature dependent behaviour which is most likely caused by biogenic emissions.

The temperature dependence of biogenic AOD is stronger in the presence of anthropogenic aerosols.

The temperature dependent biogenic AOD has significant radiative effects in the present day climate but the significance might decrease in the future, thus biogenic aerosols may not produce a strong negative climate feedback.

Multivariate statistical models in the analysis of new particle formation and growth measurement data in Po Valley, Italy – quantifying the role of organics, ammonia and sulphuric acid S. Mikkonen, T. Yli-Juuti, J. Malila, A. Heitto, H. Rinta-Kiikka, S. Decesari, J. Kontkanen, E. Nemitz, C. Braban, W. Birmili, A. Wiedensohler, J. Joutsensaari, A. Hamed, K.E.J. Lehtinen, A. Laaksonen, and A. Virtanen

The results of a multivariate regression model indicated that sulphuric acid and ammonia could explain roughly half of the variation of J1.6 between NPF days.

The results from the MABNAG growth model, shown in Figure 1, indicate that organics were the main component in modelled mass fractions.

Structural Equation Model (SEM) could approximate adequately the quickly variating J1.6 data with sulphuric acid, ammonia, relative humidity, condensation sink, ozone and NOx concentrations as model variables.

Oxidized organic compounds in atmospheric clustering N. Myllys, J. Elm, V. Hirvonen, T. Kurtén, and H. Vehkamäki

Potential cluster formation mechanisms between sulfuric acid and oxidized organic molecules with stabilizing compounds are studied using highly accurate quantum chemical methods.

The weak clustering ability of peroxyacid compounds is caused by the lack of a strong hydrogen-bond acceptor and the formation of a strong intramolecular hydrogen bond in peroxyacid monomer structure.

Carboxylic acids are the most prominent candidates of oxidized organic compounds to form stable clusters in atmospheric conditions.

Organic multi-carboxylic acids and sulfuric acid, even together with stabilizing compounds, cannot drive new-particle formation via clustering mechanisms.

Covalently-bound dimer formation reactions or highly basic compounds might be able to explain the observed gap between experimental and theoretical cluster formation rates.

Organic soil is a significant year-around source of volatile organic compounds M. Mäki, H. Aaltonen, J. Heinonsalo, H. Hellén, J. Pumpanen, J. Bäck

Organic soil is expected to be a significant VOC source due to high organic carbon content and vegetative litter, which contains easily decomposable substrates for microbial processes.

Belowground VOC concentration measurements were conducted from the organic and from the mineral soil in a Boreal coniferous forest during two measurement campaigns.

Noteworthy concentrations of monoterpenes and sesquiterpenes were measured year-around from the soil profile.

Monoterpene concentrations were found to be highest in organic soil (Fig. 1), probably released by roots, microbes, and decomposition of monoterpene rich litter.

Figure 1. The average isoprene and monoterpene concentrations (µg m-3) from the different soil horizons in 2016.

Long-term trends in particle size-distributions and new particle formation observed at San Pietro Capofiume, Italy T. Nieminen, J. Joutsensaari, V. Leinonen, S. Mikkonen, T. Yli-Juuti, P. Miettinen, A. Virtanen, K. E. J. Lehtinen, A. Laaksonen, S. Decesari, L. Tarozzi, M. C. Facchini

Aerosol number size-distributions measured from 2002 until 2017 at an anthropogenically influenced rural Po Valley site are analyzed. Statistically significant decreasing trends are observed in number concentrations of nucleation mode particles thoughout the measurement period, whereas concentrations of larger particles (in Aitken and accumulation modes) do not show decline after 2009.

The yearly number of new particle formation events does not have any clear trend, but the formation and growth rates of nucleation mode particles (3-25 nm in diameter) show a declining trend.

Ground-based LIDAR and airborne in situ measurements for studies of aerosol layers A. Nikandrova, R. Väänänen, K. Tabakova, A.Manninen, V-M. Kerminen, M. Kulmala, T. Petäjä and E. O'Connor

We present an analyses of aerosol layers in a relatively clean background measurement station obtained from a combined dataset of ground-based high spectral resolution lidar and airborne SMPS and OPS measurements.

Several elevated layers were identified from the backscatter profiles, while the size distributions were combined for these layers from observations of SMPS and OPS.

The difference between the aerosol layers was due to mixing, origin and deposition. Nucleation mode particles could be formed in the elevated layers, as there were no mixing observed between the layers.

Turbulent mixing ensures lower variability in the size distribution in the BL on short timescales, and more variability in the free troposphere.

Active sites in heterogeneous nucleation of ice O. H. Pakarinen, T. Ponkkonen, G. Roudsari, H. Vehkamäki

Heterogeneous nucleation of ice, initiated by an aerosol seed particle, is not thoroughly understood.

We have developed an atomistic model of ice crystal formation using a continuum of methods from density functional theory (DFT) to large-scale classical molecular dynamics (MD).

Results from mW potential simulations show that surface geometry alone can explain the high nucleation activity of AgI.

K-feldspar, which is considered one of the most important ice nucleation agents in the atmosphere, shows very weak ice nucleation activity from its exposed (001) surface, but instead nucleates ice (see Fig. 1.) at the (100) surface at steps.

Figure 1. Orthoclase (K-feldspar) (100) surface effectively nucleates ice. Our MD simulations shows that ice grows with the prism face aligned with the surface, in contrast to most other surfaces.

Can a pathogenic fungus disturb the water transport via surface tension in Norway spruce? T. Paljakka, K. Rissanen A. Vanhatalo, R. Linnakoski, R. Kasanen, Y. Salmon, N. L. Prisle, J. Bäck, T. Hölttä

Linking fungal infection to physics behind tree physiology is exceptional in the field of plant pathology and plant physiology, and provides an insight to the reasons causing tree mortality.

The studied fungus infection (Endoconidiophora polonica) may hinder water transport in trees by mechanical blocking in the water transport route or by decreased surface tension of water in xylem, which increases the vulnerability of tree water transport to hydraulic disturbances.

Tree water relations, including hydraulic conductivity, hydraulic conductance and surface tension of xylem sap were measured with resin pressure and volatile organic compounds (VOC) from Norway spruce (Picea abies) saplings.

The xylem hydraulic conductivity and surface tension of infected trees were lowered compared to control trees. The resin pressure showed larger variation in infected trees whereas the VOC emissions indicated yet unclear response to infection.

Figure 1. Hydraulic conductivity and surface tension of clones 64 and 1510. The abbreviation “cp” stands for the infected trees.

Fate of sulfuric acid clusters inside the APi-TOF M. Passananti, J. Kangasluoma, E. Zapadinsky, M.P. Rissanen, N. Myllys, H. Junninen, M. Ehn, M. Attoui, H. Vehkamäki

Atmospheric Pressure interface Time Of Flight mass spectrometer (APi-TOF) is a powerful instrument to detect atmospheric molecules and clusters, even at environmental low concentration. However, clusters can undergo transformation inside the instrument due to the low pressure and energetic collisions.

We are studying the fate of clusters inside the APi-TOF, and we are using the experimental data to build a model to predict the behavior of atmospheric clusters inside the mass spectrometer.

We are investigating the effect of electric field applied to the APi section on sulfuric acid cluster fragmentation and we observed a significant fragmentation in the second chamber of the APi.

Figure 1. Impact of voltages applied to the front of second quadrupole (Q2 front) on the ratio between sulfuric acid trimer (SA)3, dimer (SA)2 and monomer SA detected by APi-TOF. Research highlights (Project DAMOCLES, Monica Passananti) Atmospheric Pressure interface Time Of Flight mass spectrometer (APi-TOF) is a powerful instrument to detect atmospheric molecules and clusters, even at environmental low concentration. However, clusters can undergo transformation inside the instrument due to the low pressure and energetic collisions. We are studying the fate of clusters inside the APi-TOF, and we are using the experimental data to build a model to predict the behavior of atmospheric clusters inside the mass spectrometer. We are investigating the effect of electric field applied to the APi section on sulfuric acid cluster fragmentation and we observed a significant fragmentation in the second chamber of the APi.

Particle growth rates from nucleation mode to cloud condensation nuclei sizes M. Peltola, P. Paasonen, J. Kontkanen, H. Junninen, V.-M. Kerminen and M. Kulmala

We have generated an automatic method to determine aerosol particle growth rates in nucleation, Aitken and accumulation modes. This method increases drastically the number of analysable particle growth episodes, since it allows, in our understanding, for the first time the determination of particle growth rates for time periods not immediately following a new particle formation event.

Our results show that the maximum observed growth rate of particles in Aitken and accumulation modes increases as a function of particle size. This could be due to the particle phase chemistry of semivolatile compounds. For particles in the nucleation and Aitken modes, the growth rate was observed to correlate positively with the ambient temperature.

Figure 2. Growth rates as a function of the initial diameter of the growth episode. The colour indicates the

mean temperature during the growth event.

Formation of condensible vapours from α-pinene oxidation: effect of nox on experimentally derived volatility distribution O. Peräkylä, M. Riva, L. Heikkinen, E. Canaval, J. Enroth, L. Fischer, O. Garmash, L. Quéléver, S. Schallhart, M. Äijälä, A. Hansel, T. Petäjä And M. Ehn

We directly estimated the volatilities of HOMs formed in α-pinene oxidation.

Organic nitrates were found to be of higher volatility as compared to non-nitrates of similar mass.

In total, addition of NO shifted the volatility distribution of HOMs towards higher volatilities.

From processes to modelling of methane emissions from trees (memetre) – erc starting grant 2018-2023 M. Pihlatie et al.,

Among the natural sources, the contribution of vegetation to the global CH4 budget is the least well understood.

The main aim the project is to raise the process understanding of CH4 exchange in forests to the level where we can construct a process model for the soil-tree-atmosphere CH4 exchange.

We use novel enclosure methods, stable and radiocarbon isotopes and molecular biology techniques to investigate CH4 exchange of trees at state-of-the-art field and laboratory research stations (e.g. ICOS). The biggest breakthrough of the project is that in the end we can answer the question: how much trees contribute to the CH4 budget of boreal and temperate forest ecosystems.

Fluorescence across space and time (fast 2017): a multiscale campaign to interlink chlorophyll fluorescence and the spring recovery of boreal forests A. Porcar-Castell1, J. Atherton1, P. Rajewicz1, A. Riikonen1, S. Grebe2, L. Weiwei1,3, J. Aalto4, R. Bendoula5, A. Burkart6, H. Chen7, K.-M. Erkkilä8, J.-B. Féret5, B. Fernandez-Marin9, J.I. Garcia-Plazaola9, T. Hakala10, S. Hartikainen11, E. Honkavaara10, J. Ihalainen12, T. Julitta13, P. Kolari8, L.M.J. Kooijmans7, J. Levula4, M.H. Loponen4, A. Macarthur14, T. Magney15, K. Maseyk16, M. Mõttus17, S. Neimane11, E. Oksa18, G.B. Osterman15, I. Robinson14, M. Robson11, N. Sabater19, T. Solanki11, M. Tikkanen2, R. Mäkipää18, E.-M. Aro2, U. Rascher20, C. Frankenberg15,21, M. Kulmala8, T. Vesala8, J. Bäck8.

Linking chlorophyll fluorescence and photosynthesis across space and time, is an essential step for the interpretation of remotely sensed data.

During 2017 we conducted a long-term and multiscale campaign in SMEAR-II station to measure chlorophyll fluorescence properties along with leaf, canopy, and ecosystem functional, biochemical and structural traits.

We measured from photosynthetic proteins to satellite data. Current work is ongoing to integrate the whole dataset.

Towards long-term total OH reactivity measurements in a boreal forest A. P. Praplan, H. Hellén

In spring and summer the total experimental OH reactivity measured is much higher than the reactivity expected from quantified volatile organic compounds (VOCs).

The highest total OH reactivity values measured were in the spring during the day, while the usual diurnal pattern exhibits a maximum at night, following biogenic VOCs concentrations.

High spring total OH reactivity values are connected to soil thawing processes.

Eddy covariance instrument comparison M. Provenzale, I. Mammarella, M. Potes, R. Salgado

The Campbell Irgason is the first eddy covariance (EC) instrument that integrates the sonic anemometer and the gas analyser, thus solving the sensor separation problem.

The first studies made with this instrument yielded unrealistic results (CO2 uptake at night over lakes or vegetation). This might be caused by the fact that the Irgason spectroscopic corrections are done using the slow-response temperature instead of the fast-response one. A correction has been put forward by Campbell Scientific.

Cooperating with the University of Évora in Portugal, we ran an instrument comparison campaign, using the Irgason and a traditional EC setup over lake Vanajavesi, in the Häme region in Finland.

The results are still under evaluation, but even after applying the proposed correction there still is a clear discrepancy between the two recorded CO2 fluxes, which is dependent on the sensible heat flux.

The Irgason temperature-driven bias hence does not seem to have been fully addressed. Further work is needed in order to have reliable flux estimates from the Irgason.

Secondary organic aerosol formation from α-pinene versus real plant emissions: chemical and physical properties I. Pullinen, A. Ylisirniö, O. Väisänen, H. Liqing, A. Buchholz, S. Schoebesberger, Z. Li, E. Kari, P. Miettinen, P. Yli-Pirilä, A. Virtanen

α-pinene is often used as a proxy for real plant emissions in boreal regions.

We set out to test how similar the physical and chemical properties of SOA formed from α-pinene are to SOA formed from biogenic volatile organic compounds collected from pines (Pinus sylvestris).

SOA was produced in a batch reactor mode chamber, using either α-pinene or collected BVOC as a precursor.

Focus will be to analyse the chemical composition of the particles, and compare the hygroscopicity of SOA from different precursors.

Long term effects of fire on carbon and nitrogen pools and fluxes in the arctic permafrost and subarctic forests (arcticfire) J.Pumpanen,K.Köster,H.Aaltonen,E.Köster,X.Zhou,J.Heinonsalo,M.Palviainen,H.Sun,H.Zhang-Turpeinen,C.Biasi,V.Bruckman,A.Prokushkin,andF.Berninger

We studied the effects of tree roots and addition of glucose on the solubility of soil organic matter (SOM) using pressurized hot water extraction.

The easily soluble and non-soluble fractions showed distinctive concentrations of 13C, 14C and 15N isotopes indicating that the age of soil organic matter was not directly related to its solubility.

Roots and easily available carbon may induce soil organic matter degradation and nitrogen uptake from it.

Figure 1. (a) Measured natural isotope δ15N values in soil organic matter fractions extracted in different temperatures in the control (C), soil + glucose (G), seedling (S) and glucose + seedling (GS) treatments and (b) 14C-value in the same fractions. Figures from: Pumpanen J., Lindén A., Bruckman V.J., Berninger F., Ilvesniemi H., Oinonen J., Sonninen E., Kukumägi M. and Heinonsalo J. 2017. The effect of roots and easily available carbon on the decomposition of soil organic matter fractions in boreal forest soil. European Journal of Soil Science. doi: 10.1111/ejss.12439.

Measuring the temperature response of α-pinene-derived highly oxigenated molecules (homs) in a cold-room smog chamber L. Quéléver 1, K. Kristensen 2, L.Normann Jensen 2, B. Rosati 2,3, R. Teiwes 2,3, H. B. Pedersen 3, M. Bilde 2

And M. Ehn 1

We performed alpha-pinene ozonolysis experiments and highly oxidized molecules (HOMs) measurements at the Aarhus University Research on Aerosol (AURA) smog chamber at three different temperatures (20 °C, 0 °C and -15 °C). We observed that colder temperatures significantly curbed the rate of formation of highly oxidized materials among which specific compounds were found to experience volatility changes. The overview of the campaign, targeted toward HOMs measurements, is currently on the writing stage of a scientific paper.

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HIMMELI – HelsinkI Model of MEthane buiLd-up and emIssion for peatlands M. Raivonen, S. Smolander, L. Backman, J. Susiluoto, T. Aalto, J. Mäkelä, T. Markkanen, O. Peltola, J. Rinne, M. Aurela, M. Tomasic, E.-S. Tuittila, T. Larmola, S. Juutinen, X. Li, M. Heimann, S. Sevanto, T. Kleinen, V. Brovkin, and T. Vesala

Methane emissions from peatlands are significant for the global methane budget and the atmospheric methane concentrations.

We have developed a model that simulates peatland methane emissions, taking as input the anoxic peat respiration rate, peat temperature, water table depth and leaf area index of gas-transporting vegetation.

We tested the model, for instance, by analyzing its sensitivity to the input data.

The model simulated realistic CH4 emissions with different set-ups and can in future be tested in combination with peatland models that provide the required input.

A new optical chamber method to quantify the seasonal variation in ambient and 77k leaf-level chlorophyll fluorescence spectra P. Rajewicz, J. Atherton, and A. Porcar-Castell Chlorophyll fluorescence can be used as a tool to follow the species-specific changes in plant’s photosynthetic activity in response to temperature and light conditions.

We developed and tested an “optical chamber” method to enable comparable measurements of several optical traits of both broadleaves and needles in different temperatures.

Species-specific differences were observed in chlorophyll fluorescence signal across time, light gradients and temperature changes during season-transition.

Isoprene and monoterpene emissions from a boreal peatland during spring and early summer P. Rantala, S. Schallhart, L. Quéléver, O. Peltola, L. Ahonen, J. Levula, T. Vesala and H. Junninen

We measured for the first time BVOC (biogenic volatile organic compounds) fluxes from wetland using the eddy covariance method.

The measurements were located in Siikaneva, Finland, between March and June 2016.

All BVOC fluxes were below detection limits in March and April. From April onward:

- Isoprene fluxes in Siikaneva were almost as high as monoterpene fluxes in Hyytiälä. - Monoterpene fluxes were small, however, they had an interesting flat diurnal behavior and they

correlated with the methane fluxes.

The sensitivity of idealised baroclinic waves to environmental temperature changes M. Rantanen, J. Räisänen, V. A. Sinclair, and H. Järvinen

We have used idealised baroclinic wave simulation by the Weather Research and Forecasting (WRF) model to study how the changes in atmospheric temperature distribution due to the climate change will affect to the dynamics of extra-tropical cyclones.

The temperature forcings in the experiments were similar to what are expected in the warmer climate: 1) uniform increase of atmospheric temperature, 2) decreased lower level temperature gradient and 3) increased upper level temperature gradient.

We found out that the cyclones were most sensitive to the low-level temperature gradient decrease, whereas upper tropospheric gradient increase played a smaller role.

Uniform increase of temperature can induce also deep cyclones, but their dynamic properties (like kinetic energy) can decrease.

Transpiration regulates the emissions of water-soluble short-chained ovocs in scots pine (pinus sylvestris) K. Rissanen, T. Hölttä, and J. Bäck

In short-chained oxygenated VOCs, paritioning to aqueous phase affects their emissions from leaves.

Emissions can be directly regulated by stomatal conductance and / or by the transport of compounds in transpiration stream.

We used long-term dynamic chamber measurement data to analyse the roles and interrelations of temperature, stomatal conductance and transpiration in explaining shoot-scale emissions of methanol, acetone and acetaldehyde.

Combination of exponential temperature effect and linear transpiration effect explained best the emissions of these compounds, which highlights the importance of transport in transpiration stream in emission dynamics.

Climate.now – online learning material and multidisciplinary collaboration L. Riuttanen, Climate.now team

Climate.now is a multidisciplinary learning material about basics of climate change published online in Autumn 2016.

Climate.now material is aimed at higher education and is available online for anyone to use at www.climatenow.fi.

Multidisciplinary collaboration within climate change education is to be continued in near future.

Impact of Aerosol Acidity and Aerosol Liquid Water on Volatility and the Chemical Composition of SOA formed from Alpha-Pinene Ozonolysis M. Riva, L. Heikkinen, O. Peräkylä, S. Schallhart, J. Enroth, Matti Rissanen, M. Ehn

We systematically investigated the impact of aerosol acidity and aerosol liquid water (ALW) on the SOA formation from the ozonolysis of alpha-pinene. While the ALW does not have a notable effect, the presence of acidified particles significantly impacts the chemical composition of the SOA. As presented in Figure 1, large formation of C8HxOy were observed in the presence of wet acidic aerosols, resulting in an enhancement of the SOA formation. These preliminary results indicate that certain monomers and dimers, present in particulate phase, can further undergo acid-catalyzed reactions.

Figure 1. Relative abundance ([C]seed/[C]No seed) of the (a) C8-monomers and (b) C20-dimers observed in particle phase with (ABS or AS) and without (Org) seed. AS and ABS correspond to the injection of non- acidified and acidified seed aerosol under dry conditions, respectively. ABS-de/AS-de and ABS-h- indicate the experiments performed using ABS/AS deliquesced seed aerosol into a humid chamber and ABS dry seed aerosol un der high-RH conditions, respectively.

Observation of evening biogenic ion cluster formation events in a boreal forest C. Rose, Q. Zha, L. Dada, C. Yan, K. Lehtipalo, H. Junninen, S. Buenrostro Mazon, T. Jokinen, N. Sarnela, M. Sipilä, T. Petäjä, V.-M. Kerminen, F. Bianchi, M. Kulmala

Highly oxygenated molecules (HOMs) are essential to grow nanoparticles to cloud condensation nuclei (CCN) sizes.

It was recently reported from chamber experiments that HOMs resulting from the oxidation of monoterpenes can produce new particles in the absence of sulfuric acid via an ion induced cluster formation mechanism.

Investigating the occurrence of ion cluster formation events detected within a few hours around sunset in the boreal forest (Fig. 1), we show for the first time that monoterpenes-derived HOMs are also able to drive ion cluster formation in an ambient atmosphere, with a preference for ozonolysis products.

Impact of Aerosol Acidity and Aerosol Liquid Water on Volatility and the Chemical Composition of

SOA formed from Alpha-Pinene Ozonolysis

M. Riva, L. Heikkinen, O. Peräkylä, S. Schallhart, J. Enroth, Matti Rissanen, M. Ehn

We systematically investigated the impact of aerosol acidity and aerosol liquid water (ALW) on the SOA formation from the ozonolysis of alpha-pinene. While the ALW does not have a notable effect, the presence of acidified particles significantly impacts the chemical composition of the SOA. As presented in Figure 1, large formation of C8HxOy were observed in the presence of wet acidic aerosols, resulting in an enhancement of the SOA formation. These preliminary results indicate that certain monomers and dimers, present in particulate phase, can further undergo acid-catalyzed reactions.

Figure 1. Relative abundance ([C]seed/[C]No seed) of the (a) C8-monomers and (b) C20-dimers observed in particle phase with (ABS or AS) and without (Org) seed. AS and ABS correspond to the injection of non-acidified and acidified seed aerosol under dry conditions, respectively. ABS-de/AS-de and ABS-h- indicate the experiments performed using ABS/AS deliquesced seed aerosol into a humid chamber and ABS dry seed aerosol under high-RH conditions, respectively.

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Figure 1. Identification of an “evening” negative ion cluster formation event on 21 – 22 April 2013 using NAIS measurements. The event is seen from ~ 19:00 to midnight (local time) on the surface plot (A) as well as from the increase in ion cluster concentration in two size ranges, 1.5–2 nm and 2–3 nm (B).

The lack of photochemistry during nighttime most likely prevent the newly formed clusters from growing beyond few nanometers, however it is highly probable that atmospheric clusters would be able to reach larger sizes in such a system when photochemical processes are active.

Providing insights into these biogenic cluster formation pathways is of great interest since they might have been a widespread source of particles and CCN during the preindustrial era, and are expected to also significantly contribute to particle formation in the future.

Integrated Evaluation Of Biogenic Secondary Organic Aerosol Formation In A Global Climate-Model C. Rose, R. Makkonen, H. Junninen, P. Rantala, M. Sipilä, J. Bäck, T. Petäjä, V.-M. Kerminen, M. Kulmala

Because of our uncomplete understanding of new particle formation (NPF), global models such as ECHAM5.5-HAM2 use simplistic representations of the process. Efforts have been made during the last decades to better constrain predictions to observations in the planetary boundary layer.

For that purpose, several nucleation parameterizations were tested, including both the contribution of sulfuric acid and organics. In addition, ECHAM5.5-HAM2 has been recently upgraded to take into account the contribution extremely low volatile organic compounds (ELVOCs). However, the accuracy of the predicted precursors concentrations themselves was left behind further investigation.

Here we report such an analysis for monoterpenes and their oxidation products as well as sulfuric acid, using simulations conducted with ECHAM5.5-HAM2 and measurements performed at the boreal SMEAR II station in Hyytiälä, Finland between 2010 and 2013.

Figure 1. Median seasonal variation of measured and modelled monoterpenes concentrations and fluxes derived from the 2010 – 2013 period. Lower and upper limits of the error bars stand for the 25th and 75th percentile, respectively. Red lines and markers indicate the monthly medians of the ratios of measured to modelled monoterpenes concentrations or fluxes.

Direct comparison of modelled and measured values was achieved for monoterpenes fluxes and concentrations, early particle growth rates (1.5-3 nm) as well as particle concentration in the Aitken mode. The contributions of sulfuric acid and monoterpenes oxidation products to early particle growth were also investigated.

Good agreement between measured and modelled aforementioned variables was obtained between April and November, while significant discrepancies were observed during colder months, most likely related to underestimated leaf area index (LAI) in the model. New simulations are currently run with corrected LAI.

Heterogeneous ice nucleation by mineral dusts in mixed phased clouds: molecular dynamics simulations G. Roudsari, O. H. Pakarinen, H. Vehkamäki

The formation of ice in clouds has a major effect on their properties, and thus for precipitation and climate.

I will, first, use all-atom molecular dynamics (MD) simulation, using the Gromacs 5.1.2 software, to study ice nucleation in the presence of kaolinite.

This study helps us to obtain a precise model of the ice structure on the surface of the kaolinite. Then, I will study the role of imperfections on K-feldspars, for instance, cracks, steps and patches, in the ice nucleation. This study will help us to identify which structural materials are more efficient as an ice nucleating particle, and based on this result we will be able to suggest designs of artificial materials which are optimized for the

cloud seeding application.

Figure 1. Initial configuration of Kaolinite slab is in contact with the water film. Oxygen, silicon, aluminium and hydrogen atoms are colored in red, yellow, pink and white respectively. Development of SMEARCORE A. Rusanen, H. Junninen, P. Kolari, M. Kaukolehto

Setting up and managing the measurement data of a station is hard and there are many different ways to do it. One especially challenging aspect of it, is the volume and diversity of the data a SMEAR station produces. For example, in 2014 the SMEAR II station produced 8 TB of raw data of over 1000 measured variables. It requires considerable expertise, attention to detail and time to manage such data correctly. The SMEARCORE project is intended to make this easier and standardize the data management so that data from different stations can be accessed uniformly.

Students expectations and experience on learning of transferable skills in a research oriented intensive field course T.M. Ruuskanen, A. Lauri, L. Riuttanen, H. Vehkamäki

Partition on different CO2 sources at forest floor in an extensive trenching experiment in a Scots pine stand in southern Finland. K. Ryhti, L. Kulmala, J. Pumpanen, M. Pihlatie, J. Heinonsalo

Soil CO2 emissions originate from heterotrophic respiration i.e. the decomposition of soil organic matter by microbes and autotrophic respiration from plant roots e.g. tree and ground vegetation.

The understanding of the nature and the magnitude of the tree-related belowground carbon fluxes is needed in order to both interpret present variation in tree growth and to estimate tree growth in future.

We established a trenching experiment at the SMEARII in southern Finland in late 2012 with the intention to partition the different sources of CO2 emissions at forest floor.

The share of tree roots comprised almost a half of all CO2 emissions.

Figure 1. The different CO2 sources at the forest floor in SMEARII in 2013–2015.

Dynamics of evapotranspiration in grazed savanna grassland in South Africa

M. Räsänen, M. Aurela, V. Vakkari, J.P. Beukes, J-P. Tuovinen, P.G. Van Zyl, M. Josipovic, A.D. Venter, K. Jaars, S.J. Siebert, T. Laurila, R. Oren, G. Katul, J. Rinne and L. Laakso

On average the annual sum of evapotranspiration is higher than the annual precipitation for agrassland savanna.

Monthly evapotranspiration is related to the monthly NDVI.

The tree and grass root water uptake will be estimated from individual wetting-drying events.

Univariate and joint bias correction of temperature and precipitation: hydrological modelling perspectives in changing climate O. Räty, T. Bosshard, C. Donnelly, J. Räisänen

Climate model simulations have often biases in their inter-variable correlation structures, which should ideally be taken into account before using them as input in hydrological modeling studies.

The ability of two multivariate bias correction algorithms capable of adjusting inter-variable correlations were tested and compared with standard univariate quantile mapping from hydrological modeling perspective in changing climate.

The results from hydrological modeling experiments show that, although errors in the simulations are reduced, the improvements in relation to univariate quantile mapping are rather modest and in some cases univariate methods even outperform multivariate algorithms.

Methane oxidation in Lake Kuivajärvi T. Saarela, A.J. Rissanen, H. Jäntti, S. Aalto, M. Tiirola, J. Pumpanen, A. Ojala

Methane (CH4) forms in the anoxic lake sediment layers but majority of it is oxidized to carbon dioxide (CO2) in the oxic sediment surface. However, during hypolimnetic anoxia, the oxic sediment surface disappears and CH4 is released from the sediment to the water column.

To investigate CH4 oxidation in the water column, we measured the CH4 and CO2 gas concentrations, the stable isotopic signatures of CH4 and dissolved inorganic carbon (DIC), and the CH4 oxidation potential in the Lake Kuivajärvi water column during the open water season of 2016.

CH4 was released to the water column when hypolimnion was anoxic, but the CH4 oxidation occurring in the water column still oxidized 60% of the CH4 that was released from the sediment.

Transition in energy transfer in three-dimensional turbulent flow Ganapati Sahoo

Turbulent flows, a paradigmatic highly chaotic and out-of-equilibrium statistical system, develop either large-scale cyclonic and anticyclonic condensates (in two dimensions) or small-scales tornado-like highly non-gaussian vortex Filaments (in three dimensions). We show that even in three-dimensional fully symmetric turbulent flow it is possible to develop A critical transition among two states, one developing a large-scale Energy transfer and the second producing small-scales fluctuations only. This is achieved by changing the time-scales of hetero-chiral or homo-chiral Interactions in the flow, connecting the energy transfer behavior to the degree of mirror-symmetry in the flow. Our empirical findings must be considered as the simplest case found so far, where turbulence discontinuously changes its large-scale configuration, under the action of one single parameter.

Sugar accumulation in tree leaves under drought stress decreases net carbon assimilation Y. Salmon, A. Lintunen, A. Dayet, K. Ryhti, T. Vesala, T. Hölttä

Accumulation of sugars in tree leaves during drought has been hypothesis to decrease plant photosynthetic activity.

We tested this hypothesis on seedlings of four species: Pinus sylvestris, Picea abies, Betula pendula and Populus tremula during a lethal drought experiment.

We found that accumulation of sugars in leaves (measured by changes of osmolality) was associated with a decrease in stomatal conductance and with an increase of non-stomatal limitation to photosynthesis, both resulting in lower carbon assimilation.

Our results further suggest that impairment of carbon transport out of tree leaves might be one of the underlying mechanisms for this accumulation of sugars.

PYROFUNGI-project highlights: The effect of season, natural disturbances and geographical location on fungal communities in boreal forests soils M. Santalahti, H. Sun, K. Köster, F. Berninger, O.-M. Sietiö, T. Raffaello, F. Asiegbu, T. Laurila, T. Pennanen, A. Jumpponen, J. Pumpanen, J. Heinonsalo

The aim of this project was to identify for the first time the fungal community structure and some of their functions in in three ecosystem stations in Finland in a South-North transect in boreal forest ecosystems, by connecting high throughput 454-pyrosequence data and SOM decomposition from several aspects: spatio- temporal dynamics, natural disturbances (fire and reindeer husbandry) and geographical location.

Fungal communities were highly variable and stratified in boreal forest soils, and species-rich across the climatic gradient.

Higher microbial diversity in soil supports higher genetic potential for maintaining crucial biochemical reactions in soil.

With longer time scales, reindeer grazing may affect SOM decomposition through changes in fungal community structure and enzyme activities.

Temporal variation of VOC fluxes above a boreal forest S. Schallhart, P. Rantala, M. K. Kajos, J. Aalto, T. Petäjä, T. M. Ruuskanen, M. Kulmala

Anthropogenic emissions dominated the VOC exchange in April 2013 at SMEAR II.

During the measurements in May and June, biogenic emissions, led by methanol dominated.

Over 75% of the total emission was caused by methanol, the monoterpenes, butene & butanol and acetone.

The compounds with flux showed high variability: 12 out of 22 VOCs with exchange were just measured during one of the three measurement periods.

Quantifying physical properties of organic aerosol through desorption thermogram modeling S. Schobesberger, E.L. D’Ambro, F.D. Lopez-Hilfiker, O.-P. Tikkanen, J.A. Thornton

Mass spectrometer measurements of the chemical composition of secondary organic aerosol (SOA) particles and their controlled thermal desorption profiles (thermograms) indicate that a large fraction of SOA material has much lower volatility than the molecular compositions suggest, and support the hypothesis that oligomer formation and dissociation are key processes affecting the properties of SOA.

We developed a detailed model of the temperature-controlled evaporation of organic aerosol during these measurements to understand the shapes of the obtained thermograms, and hence the physical and chemical properties of SOA that affect these shapes.

We apply the model to measurements during chamber experiments of SOA formation following the oxidation of monoterpenes (α-pinene and Δ3-carene).

When including terms in the model to describe oligomer formation and dissociation, we are able to simulate also the more complex thermogram shapes observed for individual compositions desorbing from the SOA (Figure 1).

As a result, we are gaining quantitative insights into the dynamics of the reversible oligomerization reactions occurring in SOA.

Figure 1. Thermogram for C8H12O5 desorbing from SOA (black), and corresponding model fit (red). The shoulder at high temperatures is attributed to the decomposition of oligomers.

Land use practices and processes for clean energy: indo-norden N.J. Shurpali, Jukka Pumpanen And Perttu Virkajärvi

Finland has drafted a bold bioeconomy strategy. Therefore, biobased energy produced from biomass and waste is of particular interest for replacing fossil fuels both in the transport sector and in power (and heat) generation.

We are measuring CO2 and N2O exchange using the eddy covariance technique from a legume (red clover) and grass mixture on a mineral soil in Maaninka.

The legume grass mixture is a sink for CO2 during the 2017 growing season. Detailed data analyses on factors governing CO2 exchange, N2O flux analysis covering N2O production, consumption and emission are in progress.

Hourly distribution of NEE from the legume and grass mixture cultivated on a mineral soil at Maaninka during the 2017 growing season.

Eddy covariance measurements of CO2 and water vapor exchange from a clear-cut forest site near the SMEAR station tower in Hyytiälä are ongoing. To help better interpret NEE data from this site, soil GHG emissions using chambers, soil phyisico-chemical characteristics and vegetation data are being monitored.

The impact of plant-derived carbon flow on fungal and bacterial communities O.-M. Sietiö, H. Sun, M. Santalahti, A. Putkinen, B. Adamczyk and J. Heinonsalo

In the organic layers of boreal forest soils, carbon is stored in the form of complex polymers including recalcitrant phenolic and humic compounds.

Ectomycorrhizal and saprotrophic fungi are suggested to compete for the same substrate in boreal forest ecosystem, and exclusion of plant carbon flow is proposed to favor saprotrophs. Soil bacterial community structure in turn has been hypothesized to fluctuate according to the shifts in fungal community.

Here, we studied in three-year field experiment the effect of restriction of the photosynthetic carbon flow to the soil fungal and bacterial communities’ composition and their potential functionality.

The restriction of direct carbon flow caused changes in the community structures of both bacteria and fungi.

The Relationship Between Planetary Boundary Layer Height and Different Radiation Variables S. Sillanpää, R. Taipale, A. Manninen, M. Kulmala and D. Taipale. Planetary boundary layer (PBL) has significant impacts on climate, weather and air quality.

We used observation data from the SMEAR II station to investigate the relationship between different radiation variables and planetary boundary layer height (PBLH).

Our aim is to create a proxy for the planetary boundary layer height. We also investigate time series of radiation data and time series of ratios of different radiation data to investigate potential changes in cloud cover.

Extra-tropical cyclones in the future: idealised climate change experiments with OpenIFS V. A. Sinclair, P. Haapanala, J. Räisänen

As the climate warms, it is likely that the number, characteristics and structure of extra-tropical cyclones will change, however projections from climate models of this are uncertain.

We performed aqua-planet experiments with OpenIFS: a control simulation and an experiment where the sea surface temperature is warmed uniformly by 4K.

We used a cyclone tracking algorithm and cyclone compositing technique to create composites of the 200 most extreme cyclones in each experiment.

Increasing the SSTs, increases the precipitation but also changes the structure of the cyclone, with more precipitation occurring farther north in the warmer experiment

b

Figure 1. (a) Cyclone composite of total precipitation 24 hours before the time of maximum intensity from control simulation and (b) the difference between the SST+4K experiment and the control (mm day-1) Seasonal variations and time series of aerosol optical depth over different parts of China from space using (A)ATSR (1995-2012) and MODIS (2000-2015) L. Sogacheva, E. Rodriguez, P. Kolmonen, G. Alexandri, A.K. Georgoulias, K. Kourtidis, G. de Leeuw

Seasonal variation in Aerosol Optical Depth (AOD) over different parts of China has been revealed using the ATSR (1995-2012) and MODIS/Terra satellites (2000-2015).

Method to combine AOD time series from two instruments (ATSR and MODIS), which together cover more than 20 years of AOD satellite measurements, has been developed and applied over China.

Aerosol-cloud interactions in liquid clouds observed during BAECC campaign. K. Tabakova, E. O’Connor, D. Moisseev, V.-M. Kerminen, M.Kulmala and T. Petäjä

Our study focuses on the aerosol-cloud interactions in liquid single-layer non-precipitating clouds in the active BSOA formation zone.

We study the effect of CCN concentrations on the cloud effective radius Re changes inside the cloud at different dry air entrainment levels.

At lower CCN concentrations (0-100 cm-3) in moderately diluted clouds (dilution coefficient 0.6 ≤ k < 0.9) cloud droplet size increases 2-4 times faster than at the CCN concentrations greater than 100 cm-3.

a

In less polluted clouds the effect of dilution is evident: in clouds close to being adiabatic, cloud droplets grow by 1µm every 10 meters inside the cloud above the cloud base, while in strongly diluted clouds (0.2 ≤ k < 0.3) this happens for every 30 meters.

In clouds close to being adiabatic (0.9 ≤ k < 1.2) the effect of CCN on Re is not clear

Do biotic plant stresses induce formation and growth of new particles? D. Taipale, V.-M. Kerminen, M. Kulmala, and Ü. Niinemets

Volatile organic compounds (VOCs) affect the formation and growth of atmospheric aerosol particles.

Trees emit a variety of VOCs, but the source strength and spectra of VOCs depend on physical, environmental and biological conditions.

We constructed a new model to study the impact of biotic plant stress (see Fig. 1 for stressors) on new particle formation (NPF) and growth.

We found that the intensity of, and possibility for, NPF depend highly on the specific stressor; gypsy moth infected oak can produce more new particles than what has been observed by non-stressed boreal forest. Autumnal moth infected birch does not lead to NPF, and due to the isoprene/monoterpene ratio, it is unsure whether the investigated fungal infections lead to NPF.

Figure 1: The plant species and biotic stressors that we studied. A: Birch and autumnal moth (photo courtesy: Tero Klemola). B: Oak and European gypsy moth (photo courtesy: https://www.ecori.org/natural- resources/2015/6/23/gypsy-moth-caterpillars-take-ri-by-storm). C: Oak and oak powdery mildew (photo courtesy: Copolovici et al., Tree Physiology, 34, 1399-1410, 2014). D: Poplar and rust fungus (photo courtesy: Jiang et al., Tree Physiology, 36, 856-872, 2016).

Unsupervised classification of vertical profiles of dual-polarization radar variables J. Tiira and D. Moisseev

Vertical profiles of polarimetric radar variables can be seen as containing fingerprints of snow growth processes.We applied an unsupervised classification method on a combination of vertical profiles of polarimetric radar variables and ground temperature. The method produces profile classes with distinct, physically meaningful features.

Improving the representation of mixed-phase cloud microphysics in the icon-lem J. Tonttila, C. Hoose, J. Milbrandt, H. Morrison

The P3 mixed-phase cloud microphysics scheme is implemented into the ICON-LEM model.

The P3 scheme introduces a novel method to describe the wide range of variability in ice particle properties without having to rely on fixed particle categories with uncertain assumed properties.

The implementation of P3 in the ICON model is tested and compared with model results using a typical bulk two-moment scheme in idealized and real-case simulations.

Although the overall results have similarities, differences are identified in the microphysical properties of the clouds, which also affect cloud dynamics.

Utilizing Open Ensemble Prediction System Estimating Parameter Values of OpenIFS Lauri Tuppi, Heikki Järvinen and Pirkka Ollinaho

Ensemble Prediction and Parameter Estimation System (EPPES) was implemented in OpenEPS in order to estimate two closure parameters in OpenIFS numerical weather prediction (NWP) model. Parameter convergence tests were used as test cases to see that OpenEPS and EPPES are working together properly.

Ensemble forecasts of different sizes were used but we concentrated on small ensembles. The cost function used in the convergence tests was suitable for only one of the two chosen parameters. However, good convergence of one parameter shows that OpenEPS and EPPES are working correctly.

Figure 1. Convergence tests of two parameters: ENTSHALP (= entrainment rate for shallow convection) and ENTRORG (= entrainment rate for deep convection). Ensemble size is 3 in both panels and x-axes shows the running number of ensembles whereas y-axes show parameter values. Darkness of the dots show how much weight they have got in the estimation process. Black dots have performed well so they have got much weight and white dots have performed poorly so they have got little weight. Green lines show the values where the parameters should converge. Panel (a) shows that ENTSHALP converges only little whereas panel (b) shows that ENTRORG converges very well.

The vertical variation of Scots pine stem monoterpene and methanol emissions A. Vanhatalo, J. Aalto, H. Hellén, J. Bäck

The knowledge on BVOC emissions of woody tree parts is much more limited than knowledge on foliage BVOC emissions.

The emissions of Scots pine stem were monitored at different heights with enclosures connected to an online PTR-MS and additionally cartridge samples were collected to obtain compound-specific patterns.

Tree top emitted monoterpenes and methanol with higher rate than the lower stem within and below canopy.

There was plenty of qualitative variation in the monoterpene emissions of different heights, even in short timescales.

Novel assessment of black carbon in the eurasian arctic (nabcea) A.Virkkula, J. Paatero, E. Asmi, H. Lihavainen, J. Svensson, M. Vestenius, P. Räisänen, A. Hienola, O. Meinander, H.-R. Hannula, S. Manninen, M. Ruppel, A. Korhola, J. Tissari, O. Sippula, P. Tiitta, M. Ihalainen, H. Lamberg, K. Kupiainen, M. Savolahti, V.-V. Paunu, and N. Karvosenoja WP1 One paper has been published:

Ruppel, M. M., Soares, J., Gallet, J.-C., Isaksson, E., Martma, T., Svensson, J., Kohler, J., Pedersen, C. A., Manninen, S., Korhola, A., and Ström, J.: Do contemporary (1980–2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard?, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-357, accepted for publication in ACP. Its highlights: - the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. - according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. WP2 The present BC concentrations in air is being determined from ground-based measurements at the Pallas-Sodankylä GAW station in Finnish Lapland, and at Tiksi, Yakutsk, in the Russian Siberia and the Bolshevik island at Cape Baranova station. Snow samples will be collected from sites in northern Siberia in winter/spring 2018. No publications so far. WP 3 The evolution of physical properties and chemical composition of BC aerosols emitted from wood burning have been studied in laboratory experiments at the University of Eastern Finland (UEF). The experiments for flaring emissions aare being prepared. No publications so far. WP 4 The scenarios will be done by using the Greenhouse Gas and Air Pollution Interactions and Synergies model (GAINS, gains.iiasa.ac.at). So far the work has concentrated on creating scenario concepts with the cooperating institutesz (IIASA, AMAP), studying the existing emission inventories. No publications so far. WP5 One paper has been published: Räisänen, P., Makkonen, R., Kirkevåg, A., and Boldingh Debernard, J.: Effects of snow grain shape on climate simulations: Sensitivity tests with the Norwegian Earth System Model, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-118, in review, 2017. Its highlights: - Sensitivity tests have been conducted regarding how BC and dust radiative forcing in snow depends on the snow-grain size (volume-to- projected area equivalent radius) and the assumed snow grain shape - In general, the BC/dust forcing in snow increases with increasing snow grain size, because for larger snow grains, solar radiation penetrates deeper into the snow pack - also, the radiative forcing is smaller in the case of non-spherical than spherical snow grains (for a given snow grain size and SWE)

Lower tropospheric warm anomalies observed after precipitation over tropical oceans M. Virman, M. Bister, V.A. Sinclair, H. Järvinen, J. Räisänen

Atmospheric deep convection produces most of the precipitation on Earth.

Lower tropospheric humidity is one of the fundamental factors controlling the formation and behaviour of deep convection.

We analysed sounding and precipitation data and found that after precipitation at stations with dry low-to-midtroposphere, warm anomalies between 800-950 hPa were observed, whereas over moist stations no warm anomalies were observed even after intense precipitation.

We hypothesize that the warm anomalies formed as a result of subsidence under evaporation of stratiform precipitation falling from the anvils of deep convection.

The warm anomalies are so large that they can be detrimental for future deep convection, and hence they may offer a new explanation for the sensitivity of deep convection to lower troposperic humidity.

Measurements of the effect of cloud processing on aerosol chemical composition O. Väisänen, L. Hao, A. Ylisirniö, I. Pullinen, S. Schobesberger, S. Romakkaniemi, A. Virtanen

Cloud droplet formation can alter the aerosol chemical composition through aqueous phase processes. These processes can include for example uptake of semi-volatile chemical species through the air-liquid interface as well as reactions taking place in the cloud water.

To study the effect of cloud processing on aerosol chemical composition, we organized an intensive measurement campaign at the Puijo station in Kuopio, Finland, during the autumn 2016.

We observed slightly increased fractions of low-volatile organic species during cloud events, whereas semi-volatile species had relatively stronger contribution during cloud free conditions.

We observed cloud-condition dependent changes in inorganic composition with increased nitrate-to-sulphate and ammonium-to-sulphate ratios during cloud events.

Formation of highly oxidized multifunctional organic compounds from Chlorine radical initiated oxidation of a-pinene Yonghong Wang, Matthieu Riva, Hongbin Xie, Liine Heikkinen, Simon Schallhart, Otso Peräkylä, Chao Yan, Markku Kulmala, and Mikael Ehn

Highly oxidized multifunctional organic compounds (HOMs) formation from Chlorine radical initiated oxidation of a-pinene was investigated for the first time.

With increased NO concentration, the formation of dimers suppressed by competition reaction of peroxyl radical with NO.

Chlorinated HOMs were measured both in monomers and dimers.

Experimental investigation of aerosol particle composition and growth rates D. Wimmer, P. Winkler, C. Kuang, J. Kangasluoma, M. Kulmala,, and T. Petäjä

Here we present a simple method to determine aerosol particle chemical composition and their growth rates.

The instrument design presented here is aimed at bridging the size gap between high resolution mass spectrometry and other mass spectrometers which are used for quantifying the chemical composition of aerosol particles starting from around 5 nm in mobility diameter.

Preliminary analysis of a size resolved nano CPC battery deployed in the forest field station in Hyytiälä in southern Finland shows that the hygroscopicity of aerosol particles can be indirectly determined by using different CPCs with different working liquids together with a nano DMA.

The method works best in the 2-5 nm size range, which shows a clear difference in the concentration ratios measured by the water CPC compared to the butanol CPC.

Mass spectrometer data for the smallest clusters is also available at the Hyytiälä, which allows to follow the nucleation and growth of the aerosol particles starting from the smallest clusters to larger (>10nm) sizes.

Growth and volatility of nanoparticles at Hyytiälä in spring 2014 T. Yli-Juuti, C. Mohr, A. Heitto, F. D. Lopez-Hilfiger, J. Hong, E. L. D’ambro, S. Schobesberger, U. Makkonen, M. Rissanen, R. L. Mauldin III, M. Sipilä, M. Kulmala, T. Petäjä, I. Riipinen, J. Thorton

Growth of atmospheric nanoparticles is observed frequently, and the mechanisms related to the growth and the identity of the participating species are not known yet in detail.

We simulated nanoparticle growth based on detected organic vapor concentrations at Hyytiälä in spring 2014.

We compared the simulated growth rate to observed evolution of particle size distribution and the simulated composition to the observed volatility of the 30 nm particles.

The detected organic vapor concentrations were high enough to explain the observed nanoparticle growth, and the large contribution of the low-volatile and extremely low-volatile compounds to the simulated nanoparticle mass were consistent with observed volatility of the nanoparticles.

Testing Trace Gases and Aerosol Mass Concentration Measuring Envitems Sensors at SMEAR II Station I. Ylivinkka, H. Keskinen, T. Petäjä, P. Keronen and M. Kulmala

Data from two air quality monitoring Envitems E4100 sensors was compared with the corresponding long-term measurement data of SMEAR II station.

The correlation coefficients were low on aerosol measurements (0.112 – 0.149 for PM10 and 0.0445-0.0485 for PM2.5), and sensors underestimated the concentration by few to over ten micrograms per cubic centimetre.

Gas measurements functioned varying: concentrations for nitrogen oxides were below the detection limit of the sensors, for ozone data the correlation was hihgest but there was, however, a difference in correction factors, and one sensor overestimated and the other underestimated the carbon monoxide concentration by tens of ppb and furthermore the signal was noisy.

Correlation coefficients in meteorological variables were largest, though the was a about 7 mbars overestimation in the ambient pressure measurements.

Figure 1. Correlation plot for one Envitems sensor in PM10 measurements. Reference signal on x-axis is from on-line mass concentration monitor. Calculated Pearson’s correlation coefficient was 0.129. The green line is 1:1 line and the purple is a linear least squares fitting to the data points. Envitems underestimated the concentration especially when the mass concentration was larger. Also the noisiness of both sensors can be seen.

Bayesian classification of time series features for predicting atmospheric particle formation days M.A. Zaidan, V. Haapasilta, R. Relan, H. Junninen, P. P. Aalto, M. Kulmala, L. Laurson and A. S. Foster

Currently the most reliable way to classify New Particle Formation (NPF) event/nonevent days is through a manual visualization method, due to the noisiness of the real-world ambient data.

However, manual labor, with long multi-year time series, is extremely time-consuming and human subjectivity poses challenges for comparing the results of different data sets.

We proposed a Bayesian neural network (BNN) classifier on time-series features to determine automatically event/non-event days of NPF, trained using aerosol particle number concentration size distributions and a manually-generated database at the SMEAR II station in Hyytiälä forest, Finland.

The proposed method has a classification accuracy of 84.2 % for determining event/non-event days. In particular, the proposed method successfully predicts all event days when the growth and formation rate can be determined with a good confidence level (often labeled as class Ia days).

Figure 1. The bar chart of the successful and unsuccessful number of predicted days (validation data sets: 2010-2014)

Vertical characterization of HOMs above and below boreal forest canopy Qiaozhi Zha, Chao Yan, Heikki Junninen, Matthieu Riva, Lauriane Quéléver, Lubna Dada, Liine Heikkinen, Otso Peräkylä, Jun Zou, Clémence Rose, Yonghong Wang, Ivan Mammarella, Gaby Katul, Timo Vesala, John Crowley, Douglas R. Worsnop, Markku Kulmala, Tuukka. Petäjä, Federico Bianchi, and Mikael Ehn

Vertical characterization of HOMs has been done firstly in the boreal forest environment.

Micro-meteorology and PBL dynamics may play important roles in ground-level HOM chemistry

Boreal forest BVOCs exchange: emissions versus in-canopy sinks Putian Zhou, Laurens Ganzeveld, Ditte Taipale, Üllar Rannik, Pekka Rantala, Matti P. Rissanen, Dean Chen, and Michael Boy

A newly developed gas dry deposition model was implemented into a column chemical transport model SOSAA, by which the modeled BVOC flux at the canopy top agreed well with the measurement data.

The 12 selected BVOCs are classified into 5 categories according to their in-canopy sources and sinks, including emission, chemical production and loss, dry deposition and turbulent transport.

Dry deposition is a significant sink for most of the BVOCs studied here except monoterpenes, isoprene+MBO and sesquiterpenes.

Figure 2: Modelled relative contributions of sources and sinks for different compounds within the canopy.