two puzzles of atmospheric chemistry over the southeast us
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Two puzzles of atmospheric chemistry over the Southeast US
Jingqiu Mao (AOS/GFDL), Larry Horowitz (GFDL), Vaishali Naik (GFDL), Fabien Paulot (Harvard), Paul Ginoux(GFDL), Meiyun Lin (GFDL), Arlene Fiore (Columbia U) and the SENEX science team
Funding from NOAA CPO
What is so unique for Southeast US?
(Millet et al., 2008, JGR)(Martin et al., 2008, AE)
Surface NOx is mainly produced from anthropogenic activities
HCHO is mainly produced from biogenic emissions (isoprene in particular)
Anthropogenic + Natural
Volatile organic compounds (VOCs) in the atmosphere:carbon oxidation chain
VOC RO2
NO2
O3
organicperoxyradicals
NO
h
carbonyls R’O2
h
OH + products
organic aerosol
ROOHorganicperoxides
OHHO
2
OH, h
OH
products
EARTH SURFACE
biospherecombustionindustry
deposition
Increasing functionality & cleavage• sources of organic aerosol• sources/sinks of oxidants (ozone, OH)
OVOCs
Importance of NOx
Global Budget of Organic Aerosols
fuel/industry open fires
OH, O3,NO3 SOG SOA
POA
K
vegetation fuel/industry open fires
700
isopreneterpenesoxygenates…
30 alkenesaromaticsoxygenates…
VOC EMISSION PRIMARY EMISSION
VOC
50 20 100
20Global sources in Tg C y-1
Two-product
SOA ≡ secondary organic aerosolPOA ≡ primary organic aerosol
Current AM3 treats SOA production as yield of terpene emissions.
Aqueous reactions
?
?
Uptake on cloud droplets
or aerosols
Puzzle 1: Overestimate of ozone
Summertime ozone over eastern US is a problem for most models
(Fiore et al., 2009, JGR)
Multimodel mean
Obs from CASTNET surface sites
Northeast US
Southeast US
Multimodel mean
Obs from CASTNET surface sites
Standard AM3
(Naik et al., 2013, JGR, in press)
Similar bias was found for the maximum daily 8-hour average ozone comparison.
Overestimate of ozone is likely a chemistry problem
Previous models with assimilated meteorology field (CTM) show similar overestimate.
Models with higher resolution also show similar overestimate.
Fiore et al. (2005) attributed this bias to the treatment of isoprene chemistry in the model.
(Rasmussen et al., 2012, AE)
Puzzle 2 : Aerosols and regional cooling
Temperature trend over past century
(Portmann et al., 2009, PNAS)
1950-2006 for May-June (Unit: K/Decade)
(Leibensperger et al., 2012, ACP)
This temperature trend cannot be explained by the change in precipitation or dynamic patterns (El Niňo, NAO) (Portmann et al., 2009).
1930-1990 change in Annual Mean Surface Temperature
The cooling can be partially due to secondary organic aerosols
(Goldstein et al., PNAS, 2009)
MISR aerosol optical thickness (diff. between JJA and DJF)
MODIS aerosol optical thickness (diff. between JJA and DJF)
(Ford et al., 2013, ACPD)
Current hypothesis is that large amount of organic aerosols are produced above the surface layer.
Similar problem was found in GFDL models
(Courtesy of Paul Ginoux and Ilissa Ocko)
Optical properties from aircraft data (left) and the model (right) over Oklahoma, US
Model cannot reproduce high loading of aerosols above the surface layer!
CM 2.1
CM 3
Geophysical Fluid Dynamics Laboratory
Surface Air Temperature
OBS (GISS)
K
Stronger cooling at northern mid-latitudes in CM3, 3x less warming globally examine forcings
CM2.1
CM3
Years (1961-2000) minus (1881-1920)
(Courtesy of Larry Horowitz)
Underestimate of organic aerosol is also a chemistry problem
(Ford et al., 2013, ACPD)
Current models cannot reproduce such amount of aerosols above the surface layer.
This cannot be explained by PBL height, SO2 emissions.
New development of chemistry in AM3: (1) heterogeneous chemistry
dust
SO4
BC
OC
Standard AM3
Updated AM3
N2O5, HO2
SO4
SeaSalt
N2O5, HO2, NO3, NO2
A new framework for heterogeneous chemistry
RH(%) 0 50 70 80 90 95 99
SO4 1.0 1.4 1.5 1.6 1.8 1.9 2.2
OC 1.0 1.2 1.4 1.5 1.6 1.8 2.2BC 1.0 1.0 1.0 1.2 1.4 1.5 1.9Sea salt
1.0 1.6 1.8 2.0 2.4 2.9 4.8
Reactions Uptake coefficient (γ)
HO2 → products 1.0
N2O5 → 2.0 HNO3 0.1
NO3 → 1.0 HNO3 0.1
NO2 → 0.5 HNO3 0.0001
Hygroscopic growth factor
(Mao et al., 2013a, ACP; 2013b, GRL)
Impact of heterogeneous chemistry (AM3 C48 2001-2005)
(Mao et al., 2013a, ACP; 2013b, GRL)
Simulation (het chem on) – Simulation (het chem off)
Improvement on CO at 500 hPa
AM3 with het chem off
MOPITT
AM3 with het chem on
MOPITT (2000-2004) AM3(2001-2005)
Improvement on OH ratio (NH/SH)
obs
(Naik et al., 2013, JGR, in press)
The impact of biomass burning emissions on global OH/ozone:Implications for radiative forcing
IPCC AR4 only estimates the direct forcing from biomass burning aerosols (+0.03 ±0.12 W m-2)
Aerosol uptake has large impact on ozone production efficiency
ΔO3/ ΔCO is a measure of ozone production efficiency.
Observations
Sensitivity of tropospheric oxidants to biomass burning emissions
Global OH decreases with larger bb emissions.
Global ozone increases with larger bb emissions.
(Mao et al., 2013b, GRL)
Nonlinearity of total radiative forcing on biomass burning strength
CH4-induced O3 and H2O
Steady state CH4
Chemical indirect forcing from CH4 and CH4-induced changes in O3 and stratosphericH2O, is comparable to the cooling from biomass burning aerosolswith direct and indirect effect taken into account.
How about chemical indirect forcing from anthropogenic emissions?
New development of chemistry in AM3: (2) a new isoprene chemistry scheme
A new isoprene oxidation mechanism for global models
(Mao et al., submitted to JGR)
NO
12
34
OH
11.7%
O
MVK
First generation isoprene nitrates
O
MACRH
O
H
HCHO
88%Organic peroxides
OHOO
OO
OH
-hydroxyl peroxy radicaland isomers
-hydroxyl peroxy radicaland isomers
71% 29%
HO2 1,6-H shif t isomerization
4.7%
7.3%
12%26% 40% 66%
HOOO
HPALDs
hvOH100%
100%
C2 and C3 carbonyl compounds
ISOPO2 ISOPO2
OH recycling from isoprene oxidation has been a hot topic in atmospheric chemistry community in last 5 years!
Global Emissions (Tg/yr)
0
200
400
600
Isoprene Methanol AllAnthropogenic
VOCs
Was OH really that high over SE US during ICARTT?
(Ren et al., 2008, JGR)
OH measured by traditional method during ICARTT 2004
(Mao et al., 2012, ACP)
Part of OH signal could be due to interference, probably from biogenic VOC oxidation products!
A new method of measuring OH was deployed in Blodgett Forest
First generation of isoprene nitrates degraded to second generation nitrates!OH
ONO2
ISOPN (1,4)
OHONO2
ISOPN (1,2)
OHONO2
ISOPN (4,3)
ONO2
OH
ISOPN (4,1)
O
OH
ONO2
methylvinylketone nitrate (MVKN)
O
ethanal nitrate(ETHLN)
O
propanone nitrate(PROPNN)
O
methacrolein nitrate(MACRN)
ONO2
OH
OH/O2
OH
ONO2
OHOO
NO
OH
ONO2
OHO
OHONO2
OHOO
NO
OHONO2
OHO
ONO2
OH
OHOO
NO
ONO2
OH
OHO
OHONO2
OHOO
NO
OHONO2
OHO
OH/O2OH/O2OH/O2
O2NO
O2NO
Second generation isoprene nitrates (C3-C4)
First generation isoprene nitrates (C5)
C5 alkyl nitrate is short-lived due to oxidation by OH and ozone, with photochemical lifetime of 2-3 hrs.
(Paulot et al., 2009a,b)
NOy budget in eastern U.S. boundary layer for July 2004
Species Emission Chemical(P-L)
Dry Deposition
Wet Deposition
Net Export
NOx 386 -337 44 ------ 5PANs 24 13 ------ 11∑ANs ANs 18 7.4 3.6 7 R4N2 10 0.5 ------- 10HNO3 277 180 110 -3
Organic compounds may have much larger impact on global nitrogen cycling than previously thought!
Funded by NOAA CPO program, titled “Impact of organic nitrate chemistry on air quality and climate: past, present and future atmospheres” for 2013-2016.
Export of ∑ANs > Export of PANs
New chemistry
Previous studies without NOx recycling
Anthro NOx emissions in 2004
Reduce anthro NOx emissions of 2004 by 50%
Isoprene↑NOx ↓OH ↓O3 ↓ due to O3+ISOP
Surface ozone response to isoprene emissions:Implications for future air quality
NOx emissions↓
Sensitivity of ozone to isoprene emissions ↓
(Mao et al., submitted to JGR)
NOx emissions has been reduced by 34% from 2005 to 2011
OMI NO2 column in 2005 (summer)
OMI NO2 column in 2011 (summer)
difference
(Russell et al. 2012, ACP)
AM3 with updated chemistry
Updated chemistry Standard AM3 Observations
CASTNET sites
Improvement on ozone over SE US
(Naik et al., 2013, JGR, in press)
• Bias is reduced from 12.9 ppbv to 3.3 ppbv.• This should be reexamined by MDA8 ozone. Model tends to overestimate
monthly mean ozone.
Standard AM3 New chemistry in AM3
(C48 2001-2005)
Field studies over Southeast US in this summerSENEX (NOAA)
SOAS (NSF & EPA)NOMADSS (NCAR)
Two aircrafts based at Smyrna, TN and a tower located at Centerville, Alabama.
Measurements include VOC, NOx, ozone, aerosols, CCN etc.
GFDL will submit C180 nudge simulations to SENEX data archive.
A modeling workshop to be held in Rutgers U.
GFDL AM3 configuration for SENEX• Fully coupled chemistry-climate model
o Parameterizes aerosol activation into liquid cloud dropletso solves both tropospheric and stratospheric chemistry over the full domain
• Nudging wind with GFS meteorological field• High resolution (50 x 50 km) and coarse resolution (200 x 200 km)• MEGAN biogenic emissions (process-based emission)• Anthropogenic emissions use RCP 8.5 scenario (0.5 x 0.5 degree)• New heterogeneous chemistry (Mao et al., 2013a, ACP; 2013b, GRL)• New isoprene chemistry (Mao et al., submitted to JGR)
C48 (200 x 200km) C180 (50 x 50km)
Monthly mean ozone for July of 2012
Model of Emission of Gases and Aerosols from Nature (MEGAN)Process-based emission inventory
ageLAIPART
Temperature dependence Light dependence
Leaf age
6
1iiiE
Emission factor
Fractional coverage
Leaf Area Index
HCHO measurements in boundary layer for all flights in June
Monthly mean surface HCHO concentrations for June of 2012
Preliminary results from aircraft observations and AM3 C180 nudging simulation
One flight on June 03, 2013
Ozone (obs vs. model)
HCHO (obs vs. model)
Model does not show ozone bias.Model shows good agreement with HCHO.
Time Time
Flight altitude
1. Evaluate anthropogenic and biogenic emissions in AM3 over southeast US (aircraft, model and satellite).
2. Evaluate model simulation of ozone, SOA precursors from aircraft and ground measurements.
3. Implement a new module of in-cloud SOA processing from Liu et al. (2012).
4. Evaluate organic aerosol simulations (organic aerosols in particular) and its implications for future and past atmosphere.
The “role of aerosols in regional climate” was recently identified as an important crosscuttingresearch challenge for NOAA in the report “Toward Understanding and Predicting RegionalClimate Variations and Change”.
AM3 simulations on SENEX campaign
A new module of in-cloud SOA production developed in AM3 (Liu et al., 2012, JGR)
Question: What are the formation mechanisms of secondary species (ozone, sulfate and organics) in the SE U.S.?
We implemented a new set of chemistry in AM3, which significantly improves model simulation of ozone over SE US.
This updated chemistry show significant impact on global OH, CO, O3, nitrogen cycling, and have important implications on predicting future climate change and air quality.
GFDL is participating NOAA SENEX campaign with C180 nudging model.
Overestimate of ozone (puzzle 1) may be significantly improved from this study
Underestimate of organic aerosols (puzzle 2) can be at least partly improved in the model.
Conclusions
Sunrise
Entrainment zone
Model shows large amount of VOCs and OVOCs in the residual layer.
Is it possible to do a early morning flight to see the entrainment zone?
Boundary layer structure by Stull (1988).
Does nighttime chemistry affect global nitrogen/ozone budget?
Sunset
HCHO yield at different NOx conditions
Computed in a photochemical box model. Initialized with 1ppb isoprene.O3 (40ppb), CO (100ppb), and NOx are held constant.
Prompt HCHO formation, important for deriving isoprene emission from satellite observations.
Yield of HCHO is lower at lower NOx concentrations, according to the model.
But the model could be wrong!
SO4
NOxBVOCs
Current limitation: We have no constraints on these SOA precursors.
BC
OC
Aqueous reactions in cloud droplets
Direct uptake of organic compounds by aerosols
SOA precursors(Glyoxal, methyl glyoxal etc.)
SOA
Cloud evaporates
SOA
Two new pathways for SOA formation
O3
O2
O3
OH HO2
h, H2O
Deposition
NO
CH4, CO, VOCs
NO2
STRATOSPHERE
TROPOSPHERE
8-18 km
Tropospheric ozone chemistry
Air Quality
Climate
h
h
Annual average aerosol loading from IMPROVE site
Ammonium sulfate Organic aerosols
Surface measurements show low fraction of organic aerosols
NO3
ONO2
OO
NO3
ONO2
O
ONO2
O
OH
O2NO
O
R4N2
Nighttime chemistry
Based on Rollins et al. (2009) and Xie et al. (2012)
Nighttime yield of organic nitrates is 70%>> daytime yield (11.7%)
This chemistry was implemented in GEOS-Chem
Ozone in the boundary layer during ICARTT 2004Observations Model
Obs vs. ModelImproved O3-CO correlations due to:1. Recycling of NOx
from isoprene nitrates
2. HO2 uptake (lower OH and increase NOx lifetime).
(Mao et al., submitted to JGR)
Mean vertical profiles during ICARTT
O3 has no bias in boundary layer and free troposphere.HCHO provides good constraint on isoprene emissions.
ObservationsModel (GEOS-Chem)
(Mao et al., submitted to JGR)
Total organic nitrates excluding peroxyacylnitrates (∑ANs)
Model well reproduced ∑ANs.
∑ ANs is dominated by secondary organic nitrates(C3-C4).
∑ANs vs. HCHO ∑ANs vs. O3
Model well reproduced ∑ANs vs. HCHO and ∑ANs vs. O3 correlations.
These correlations cannot be reproduced by a fast isomerization channel of ISOPO2.
Vertical profiles Speciation of ∑ANs
SENEX 2013 field campaignSoutheast Nexus
Studying the Interactions Between Natural and Anthropogenic Emissions at the Nexus of Climate Change and Air Quality
Where: Southeast U.S.When: Summer 2013What: The focus of NOAA's field study includes GFDL modeling and ESRL CSD measurements using the NOAA WP-3D aircraft.Who: Investigators in this project include researchers from several universities, industries, and governmental agencies.
temperature, radiation, land use
Human activity
Air Quality
climate
ozone, aerosols
NOx
SO2
Isoprene emission to future climate and air quality
Biomass burning
isoprene emission
Lightning
NOx
CONH3
NOx
Isoprene oxidation process
Isoprene nitrates
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