TROPOSPHERIC AEROSOLS

Part II: secondary aerosol

Species Natural processes anthropogenic Present burden vs pre-industrial

Elements of climate affecting emissionsPrimary particles        

Mineral dust Wind erosion Land use change, industrial dust

Incr. Changing winds and precipitation

Sea salt Wind     Changing winds

Biolog. Part. Wind, biolog. processes

Agriculture ??? Changing winds

Carb. Part. Vegetation fires Fossil fuel & biomass burning

Incr. Changing precip.

Secondary        

DMS Phytoplankton degradation

  More sulfate Changing winds

SO2 Volc emissions Fossil fuel comb. More sulfate  

NH3 Microbial activity Agriculture More ammonium nitrate

 

NOx Lightning Fossil fuel comb. Incr. nitrate Change in convective activityVOC Vegetation Industrial

processesIncr. Org. aerosol  

Aerosol properties

Gas emissions leading to secondary aerosol

• Dimethylsulfide (DMS) (DMS)

• SO2 emissions from volcanoes

• Industrial SO2 emissions

• Nitrogen oxides and ammonia

• Volatile Organic compounds (VOC)

DMS, DMS, (CH3)2S, is the major one of is the major one of

biogenic gases emitted from seabiogenic gases emitted from sea

• is produces during decomposition of dimethyl-is produces during decomposition of dimethyl-

sulfonpropionate (DMSP) from dying phytoplanktonsulfonpropionate (DMSP) from dying phytoplankton

•mean residence time is about 1-2 days - most of S from mean residence time is about 1-2 days - most of S from

DMS is also re-deposited in the oceanDMS is also re-deposited in the ocean

• only small fraction lost into the atmosphereonly small fraction lost into the atmosphere

Dimethylsulfide

• Recent global estimates of DMS flux from the oceans range from 8 to 51 Tg S a-1

• This is 50% of total natural S-emissions (presently nearly equivalent to anthropogenic emissions, 76 Tg S a-1)

- Differences in the transfer velocities in sea-to-air calculations

• Uncertainties are due to:- DMS seawater measurements (paucity of data in

winter months and at high latitudes)

DMS and Climate

• DMS is emitted by phytoplankton as a natural biproduct of metabolism– Possibly related to radiation protection

• Gives sea water its characteristic smell• Forms much of the natural aerosol (sub-micron

particles) in oceanic air• DMS is the major biogenic gas emitted from sea

and the major source of S to the atmosphere. It contributes to the sulfur burden in both the MBL and FT.

Figure adapted from Charlson et al. (1987) “Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate” Nature, vol. 326, pp. 655-661

The CLAW Hypothesis(Charlson, Lovelock, Andreae and Warren, 1987)

• DMS from the ocean affects cloud properties and can feedback to the plankton community

• This acts to regulate climate by increasing cloud albedo when sea-surface temperatures rise.

Sea-to-airtransport

Ocean DMS

AtmosphereDMS

Atmosphericchemistry

Aerosol Cloud Properties(albedo and lifetime)

Cloudphysics

SurfaceTemperature

and Light

Impact of cloudon atmosphericradiation

PlanktonCommunity

Conditions in thesurface ocean

Biological andchemical

interactions

Backdrop from the NOAA Central Library Photo Collection

DMS oxidation

• The atmospheric oxidation pathways that lead from DMS to ionic species (essentially sulfate and methanesulfonic acid, MSA, CH3SO3H) are complex and still poorly understood

• The first step to sulfate is SO2

• SO2 is largely dominant vs MSA, except at high latitudes (reasons unclear)

• MSA is unique for tracing marine biological activity, since it has no other source

About atmospheric SO2

• SO2 has several sources: - either natural: marine MSA and volcanism- or anthropogenic: mining and fossil fuel burning• Its oxidation ways to SO4

-- are still matter to investigation, in particular with the aid of S & O stable isotopes

• This can occur either in the gaseous phase by OH radicals or in the liquid phase by O3 or H2O2 .

• Generally gaseous phase process is dominant, except in regions of high sea salt concentrations

0% 50% 100%

Percent (%) change in concentrations (yearly average)

Case A: SO2/SO42- concentration without sea-salt chemistry

Case B: With sea-salt chemistry

SO2 (decrease) SO42- (small increase)

|100|

CaseA

CaseBCaseA

Effect of sea-salt chemistry on SOEffect of sea-salt chemistry on SO22 and and

SOSO442-2- concentrations concentrations

50%0% 100%

Effect of sea-salt chemistry on gas-phase Effect of sea-salt chemistry on gas-phase sulfate production ratessulfate production rates

|100|

CaseA

CaseBCaseA

Mar/Apr/May Jun/Jul/Aug

Sep/Oct/Nov Dec/Jan/Feb

Percent (%) decrease (seasonal average):

Aqueous versus Gas Phase OxidationAqueous versus Gas Phase Oxidation

Biological regulation of the climate?

(Charlson et al., 1987)

DMSOH

NO3 SO2 H2SO4OH

New particle formation

CCN

H2O2

Light scattering

Gas-phaseAqueous-phase

Aqueous-phase

O3

SO2 emissions from volcanoes (1)

• Volcanoes are a major natural source of atmospheric S-species

• Injections are generally occurring in the free troposphere

• Most active volcanoes are in the Northern Hemisphere (80%)

• The strongest source region is the tropical belt, in particular Indonesia

• Emissions are in the form of SO2, H2S and SO4

--

SO2 emissions from volcanoes (2)

• 560 volcanoes over the world are potential SO2 sources, but only a few have been measured

• Volcanic activity is sporadic, with a few cataclysmic eruptions per century

• Cataclysmic eruptions inject ash particles and gases (mainly SO2) into the stratosphere, where H2SO4 formed forms a veil (« Junge layer »)

Volcano locations

Continuously erupting volcanoes

Atmospheric impact of volcanoesSO2 relatively insoluble, resists

tropospheric washout

Injected into the stratosphere in large quantities (Pinatubo, 1991 ~20 Tg)

In stratosphere, SO2 oxidises to produce sulfuric acid aerosols (H2SO4)

Conversion of SO2 to H2SO4 slow (months), aerosol cloud replenished months after eruption

• The total amount of volcanic tropospheric S-emissions is presently estimated at:

14 +/- 6 Tg a14 +/- 6 Tg a-1-1

Mean volcanic sulfur emissions are of comparable importance for the atmospheric sulfate burden as anthropogenic sources because they affect the sulfate concentrations in the middle and upper troposphere whereas anthropogenic emissions control sulfate in the boundary layer.

S-isotope measurements in central polar regions (i.e. in the free troposphere) seem to support the important role of volcanic sulfur

Acid aerosols reside in the stratosphere for several yearsAerosol veils increase optical depth of the atmosphere (inc. optical depth of 0.1% = 10% reduction sunlight reaching Earth surface). Spread around the globe by stratospheric winds

Injection of acid aerosols into stratosphere is the

fundamental process governing the atmospheric impact of

volcanic eruptions

Volcanic aerosol and global atmospheric effects

Atmospheric effects of volcanic eruptions

1. Tropospheric cooling due to increased albedoEffects of aerosols can be direct or indirectAlbedo increased indirectly when aerosols fall out of the stratosphereNucleate clouds in troposphere - increase albedoRecent major volcanic eruptions produced significant cooling

anomalies (0.4-0.7oC) in the troposphere for periods of 1 to 3 yearsMagnitude of volcanic effects masked by natural variations (e.g. El

Nino)

2. Stratospheric warmingAcid aerosols absorb incoming solar radiation, heating the tropical

stratosphere, e.g. Mt. Agung (1963), El Chichon (1982), and Pinatubo (1991) all caused warming of the lower stratosphere of ~2oC

3. Enhanced destruction of stratospheric ozone

El Chichon Pinatubo

Lower stratospheric temperature (global mean)

Localised heating in the stratosphere can influence how far volcanic aerosol veils spread, by influencing stratospheric wind patterns

+3oC

-3oC

0oC

Stratospheric warming

Volcanoes do not inject chlorine into the stratosphere.Aerosols improve efficiency with which CFC`s destroy ozone,by activating anthropogenic bromine and chlorine, indirectly leading to enhanced destruction of stratospheric ozone

Relatively short lived - aerosols last only 2-3 years in the stratosphere

Reduction in ozone following the June 1991 eruption of Pinatubo

Enhanced destruction of stratospheric ozone

Several factors combine to determine whether a volcanic eruption has the

potential to influence the global atmosphere

1. Eruption styleEnergetic enough to inject aerosols into the stratosphereLarger eruptions do not necessarily have greater effects

Increased SO2 results in larger particles, not moreFall from the stratosphere faster, smaller optical depth per unit

massvolcanic effects on the atmosphere may be self-limiting

2. Magma chemistryImportance of acid aerosols means that large eruptions of

sulphur-poormagma less significant than sulfur-rich magmas

e.g. Mt St Helens - sulfur poor - negligible global effects

Atmospheric “effectiveness”

3. LatitudeProximity to the stratosphere: smaller eruptions at high latitude can inject as much SO2 into the stratosphere as larger eruptions at lower latitudes

Stratospheric dispersal: Aerosols from tropical eruptions have the potential to spread around the globe (e.g Pinatubo). Atmospheric influence of eruption outside the tropics is contained within the middle and polar latitudes of the hemisphere of origin

Atmospheric“effectiveness”

Atmospheric processes are complex !

Understanding how an atmospheric perturbation influences climate and weather is still problematic, even for largest eruptions

However, understanding how volcanoes effect climate necessary to isolate other forcing processes

Comparison of chronology of known eruptions and climatic data shed light on the ways climate responds to large volcanic eruptions

Volcanic eruptions and climate

1. The written recordCompare eruption chronologies with written records of unusualclimatic eventse.g. Benjamin Franklin (1784) ``During several months of the summer of the year 1783, when the effects of the Sun`s rays to heat the Earth should have been the greatest, there existed a constant fog over all of Europe, and great parts of North America.`` => 1783 - Laki fissure eruption, Iceland

Disadvantages: record only a couple of thousand years, humans unreliable, eruption chronologies incomplete, geographical bias (e.g. no humans = no record)

Making the connection

2. Ice cores

Acid aerosols fall on ice fieldsAccumulation of ice preserves information - acidity profileClimatically significant eruptions can be identified with great precision

Advantages: objective, precise, records `climatically significant` eruptions onlyDisadvantages: Which eruptions and why? Only those with high sulfur contents. Geographical bias. HALF of known large eruptions not recorded in Greenland ice cores

Making the connection

3. Tree rings

Proxy witnesses to eruptionsTemperate trees record passage of seasons in growth rings - dendochronologyChanges in ring spacing, frost damage correlate with known eruptions

Advantages: Trees, are old! Record extends back thousands of years. Objective, preciseDisadvantages: Tree growth sensitive to things apart from climate. Local environmental factors significant

Making the connection

20 km3 of pyroclastic material in a Plinian column 40 km high

Aerosol veil circumnavigated the globe in ~2 weeks

Initially confined to the tropics, later spread to higher latitudes in

both hemispheres

Caused spectacular sunsets worldwide

20% fall in radiant energy reaching Europe after the eruption

Average Northern Hemisphere cooling of 0.25oC, more pronounced at

higher latitudes (-1oC)

Case study: Krakatau, 1883

50 km3 of pyroclasts, Plinian column 43 km high

Aerosol veil reached London in about 3 months

Many climatic effects attributed to Tambora

1816 - `the year without a summer`inspired `Frankenstein`

Anomalously cold winter in North America and Europe

Widespread crop failures, famine

Case study: Tambora, 1815

Global sulfur emissions

Global sulfur emissions latitude emissions.gif

GLOBAL SULFUR EMISSION TO THE ATMOSPHERE (1990 annual mean)

Chin et al. [2000]

Industrial SO2 emissions

• During the last decade, researchers from different countries have prepared separate country-level inventories of anthropogenic emissions (GEIA= Global Emission Inventory Activity). In regions were local inventories were not available, estimates based on fossil fuel consumptions and population were calculated.

In 1985: about 81% of anthropogenic sulfur emissions were from fossil fuel combustion, 16 % from industrial processes, 3 % from large scale biomass burning and 1% from the combustion of biofuels, but these figures have to be revised for more recent years.The total amount for 1985 is estimated at :

76 Tg S a76 Tg S a-1-1, accurate to 20-30%

Anthropogenic sulfur emissions

Future SO2 emissions in Asia are likely to be much lower than the latest IPCC forecasts

Sources of nitrogen oxidesand ammonia

Aircraft

0.5

NOx: ~32 TgN anthropogenic ~11 TgN natural

Fluxes in TgN/year

Nitrogen oxides

• They are important in atmospheric oxidant chemistry

• They are precursors for nitric acid which is a contributor to atmospheric acidity and reacts with NH3 and alkaline particles

Global NOx emissions (Tg/yr)

A century of NOx emissions(van Aardenne et al., GBC, 15, 909, 2001)

1890: dominated bytropical

biomass burning

1990: dominated bynorthern hemisphere

industrialization

Global NOx from lightning

Ammonia NH3

4. Ammonia is the primary basic (i.e. not acidic) gas in the atmosphere, and after N2 and N2O, the most abundant nitrogen containing gas in the atmosphere

• The significant sources of NH3 are animal wastes, ammonification of humus, emissions from soils, loss of fertilizer from soils and industrial sources – see next table

• The ammonium ion, NH4+ is an important component of

continental tropospheric aerosols (as is NO3-) forming NH4NO3

• NH3 is highly water soluble and therefore has a residence time in the troposphere of around 10 days

– Consequently, atmospheric concentrations of NH3 are quite variable, typically ranging from 0.1 to 10 ppb

Global NH3 emissions

Global NH3 sources

VOC = Volatile Organic Compounds

• Natural biogenic and anthropogenic sources• -Anthropogenic: alkane, alkenes, aromatics and

carbonyls• -Biogenic: isoprene, mono-and sesquiterpenes, a

suite of O-containing compounds• They produce secondary organic particles• Based on emission inventories and laboratory data,

the production of secondary organic particulate from VOC is estimated to:

30 to 270 Tg a-1

Spatial and temporal development of VOC emissions

(Klimont et al., Atmos. Environ., 36, 1309, 2002)

0%

20%

40%

60%

80%

100%

China1995

China2020

EasternEurope1990's

EasternEurope2020

Japan1990's

Japan2020

WesternEurope1990's

WesternEurope2020

Miscellaneous

Transport

Solvent use &chemicalindustryFossil fuelprocessing &distributionStationarycombustion

Conclusion: Integrated observation and modeling programs like INDOEX, TRACE-P, and ACE-Asia

improve our understanding of emissions …Experimental

measurements

Theoreticalmodeling

… but we desperately need more source testing in the developing worldRepresentativeness of entirepopulation of sources

Typical operating practices

Typical fuels and fuel characteristics

Relationship to similar sources in the developed world

Daily and seasonal operating cycles

Barry J. HuebertDepartment of OceanographyUniversity of Hawaiihuebert@hawaii.edu

The Real Authors:Steve Howell, Byron BlomquistLiangzhong Zhuang, Jackie HeathTim Bertram, Jena KlineACE-Asia Science Team

Supported by the US NSF& 35 other agencies

A Few Insights on Air Pollution and Climate from ACE-Asia

ACE-Asia Ob jectives:

Characterization: Determine the phy sical, che mical, andradiative properties of the m ajor aerosol types in the Ea stern A siaand Northwest Pacific region and inves tigate the relationshipsamong the se properties.

Radiation: Quant ify the interactions between aerosols andradiation in the Eastern Asia and Northwest Pacific region

Processes: Quant ify the phy sical and chemical p rocessescontrolling the evo lution o f the major aerosol types and inparticular of their phys ical, chemical, and radiative properties.