SOME CHEMICAL PROBLEMS IN ATMOSPHERIC CHEMISTRY MODELS

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SOME CHEMICAL PROBLEMS IN ATMOSPHERIC CHEMISTRY
MODELS
Daniel J. Jacob
with in order of appearance Rokjin Park, Colette
L. Heald (now at UC Berkeley), Tzung-May Fu,
Paul I. Palmer (now at U. Leeds), Dylan B.
Millet, Rynda C. Hudman, Noelle E. Selin,
Christopher D. Holmes
and funding from EPRI, EPA, NSF, NASA
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GEOS-Chem GLOBAL 3-D CHEMICAL TRANSPORT MODEL

• Driven by assimilated meteorological data from
  NASA Global Modeling and Assimilation Office
  (GMAO) with 3-6 hour resolution
• Horizontal resolution 1ox1o to 4ox5o , 50
  vertical layers
• Applied to wide range of problems tropospheric
  oxidants, aerosols, CO2, methane, hydrogen,
  mercury, exotic speciesby over 20 groups in N.
  America, Europe, Australia

• Flagship tropospheric ozone-aerosol simulation
  includes 120 coupled species, 500 chemical
  reactions
• Serves grander purposes (1) boundary conditions
  for EPA CMAQ regional model , (2) global chemical
  data assimilation at GMAO, (3) effects of climate
  change through interface with GISS GCM, (4)
  construction of Earth system model through
  NASA/GMI

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OUR FIRST ORGANIC CARBON (OC) SIMULATION FOR THE
UNITED STATES
Park et al. 2003
annual
U.S. source 2.7 Tg yr-1
10 terpenes
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FIRST MASS CONCENTRATION MEASUREMENTSOF OC
AEROSOLS IN FREE TROPOSPHERE
ACE-Asia aircraft data over Japan (April-May 2001)
Observed (Russell)
Chung and Seinfeld scheme
OC/sulfate ratio

• Observations show 1-3 mg m-3 background
• model too low by factor 10-100

Heald et al. 2005
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ITCT-2K4 AIRCRAFT CAMPAIGN OVER EASTERN U.S. IN
JULY-AUGUST 2004
water-soluble organic carbon (WSOC) aerosol
measurements by Rodney J. Weber (Georgia Tech)
Alaska fire plumes
2-6 km altitude
Values 2x lower than observed in ACE-Asia
excluding fire plumes gives mean of 1.0 mgC m-3
(3x lower than ACE-Asia)
Heald et al., in prep.
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MODEL OC AEROSOL SOURCES DURING ITCT-2K4
Large fires in Alaska and NW Canada 60 of fire
emissions released above 2 km (pyro-convection)
Heald et al., in prep.
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ITCT-2K4 OC AEROSOL VERTICAL PROFILES
Total Biomass burning Anthropogenic Biogenic SOA
Observations Model
hydro- phobic
SOx SO2 SO42- efficient scavenging during
boundary layer ventilation
Data filtered against fire plumes (solid) and
unfiltered (dotted)
Model source attribution
Heald et al., in prep.
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CORRELATION OF OBSERVED FREE TROPOSPHERIC
WSOCWITH OTHER CHEMICAL VARIABLES IN ITCT-2K4
No single variable gives R gt 0.37, but toluene
bivariate correlations with sulfate, acetic
acid, and HNO3 give R gt 0.7. No correlation with
isoprene oxidation products
Suggest aqueous-phase mechanism involving
aromatics
Heald et al., in prep.
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ALTERNATE MECHANISM FOR SOA FORMATIONAQUEOUS-PHA
SE OXIDATION AND POLYMERIZATION OF DICARBONYLS
Isoprene 350 TgC/yr (Y 4.5) 16 TgC/yr
AQUEOUS PHASE
H 4x105 M atm-1
glyoxal
Monoterpenes 100 TgC/yr (Y 0.09) 0.9 TgC/yr
CHOCHO
CH(OH)2CH(OH)2
t 1.3 h
Aromatics 20 TgC/yr (Y 20) 4 TgC/yr
Oxidation Polymerization
Oxidation by OH Photolysis Deposition
Liggio et al. 2005, Lim et al. 2005, Hastings
et al. 2005 Kroll et al. 2005
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MODEL REPRESENTATION OF AQUEOUS-PHASE SOA
FORMATION USING REACTION PROBABILITY g APPLIED TO
GLYOXAL
Liggio et al. 2005
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GEOS-Chem glyoxal and methylglyoxal in surface
air (July)
Production isoprene, monoterpene,
aromatics Loss photolysis, oxidation No aerosol
uptake, dry/wet deposition yet
GLYX ppb at 0E
Z (km)
0.28 ppb
MGLY ppb at 0E
Z (km)
0.56 ppb
Tzung-May Fu, Harvard
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OXYGENATED VOCs OVER TROPICAL PACIFIC
(PEM-TROPICS B DATA)
SH
Singh et al. 2001
Methanol and acetone are the principal
contributors
NH
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GLOBAL MODEL BUDGET OF METHANOL (Tg yr-1)with
(in parentheses) ranges of previous budgets from
Singh et al. 2000,Heikes et al. 2002,
Galbally and Kirstine 2003, Tie et al. 2003
CH3O2 (85) RO2 (15)
OH
CH3OH lifetime 10 days (5-12)
130
VOC
CH3O2
Atmospheric production 37(18-31)
OH(aq) - clouds
lt1 (5-10)
Dry dep. (land) 56 Wet dep. 12
NPP based, x3 for young leaves
Ocean uptake 11 (0-50)
Plant growth 128 (50-312)
Biomass burning 9 (6-13) Biofuels 3
Urban 4 (3-8)
Plant decay 23 (13-20)
Jacob et al. 2005
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SIMULATED METHANOL CONCENTRATIONS IN SURFACE AIR

• Representative observations
• In ppbv Heikes et al., 2002
• Urban 20 (lt1-47)
• Forests 10 (1-37)
• Grasslands 6 (4-9)
• Cont. background 2 (1-4)
• NH oceans 0.9 (0.3-1.4)

Tropics obs model Rondonia
1-6 10 Costa Rica 2.2
2.1
Jacob et al. 2005
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METHANOL VERTICAL PROFILES OVER S. PACIFIC
obs. From H.B. Singh
Could the atmospheric source from CH3O2 CH3O2
be underestimated?
HO2
CH3OOH
70
OH
In model over S. Pacific,
NO
CH4
CH3O2
20
HCHO
CH3O2
5-10
0.6 CH3OH
Photochemical model calculations for same data
set Olson et al., 2001 are 50 too high for
CH3OOH, factor of 2 too low for HCHO
Could there be a biogenic VOC soup driving
organic and HOx chemistry in the remote
troposphere?
Jacob et al. 2005
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GLOBAL GEOS-CHEM BUDGET OF ACETONE (Tg yr-1)from
Jacob et al. 2002 with photolysis update from
Blitz et al. 2004
hn
propane i-butane
OH
(CH3)2CO lifetime 15 days 18 days
46
28
21 (16-26)
OH
OH, O3
terpenes MBO
7 (3-11)
27
37
Dry dep. (land) 9
12
Ocean uptake 14 19
Ocean source 27 (21-33)
microbes
DOChv
Vegetation 33 (22-42)
Biomass burning 5 (3-7)
Urban 1 (1-2)
Plant decay 2 (-3 - 7)
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OCEANIC SOURCE OF ACETONE IN MODELNEEDED TO
MATCH OBSERVATIONS OVER S. PACIFIC
from Jacob et al. 2002
obs from Solberg et al. 1996
obs. From H.B. Singh
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BUT MORE RECENT AIRCRAFT DATA IMPLY A NET
OCEANIC SINK FOR ACETONE
TRACE-P observations over tropical North Pacific
in spring Singh et al., 2003
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CORRELATION OF ACETONE WITH TRACERS OF SOURCES IN
ASIAN OUTFLOW (TRACE-P DATA)
Multiple regression
Continental source
Propane source
Acetone b0 b1 Ethane b2 HCN b3
Methanol
Acetone pptv
Acetone pptv
Intercept 200 pptv
CO pptv
Ethane pptv
Acetone b0 b1 CO b2 HCN b3
Methanol
Biomass burning source
Acetone pptv
Acetone pptv
Biogenic source
Intercept 238 pptv
How to explain the pervasive 200 pptv acetone
background?
Methanol pptv
HCN pptv
Tzung-May Fu (Harvard)
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HCHO COLUMN DATA FROM OMI SATELLITE INSTRUMENT
July 2005
Thomas Kurosu (Harvard/SAO) and Dylan Millet
(Harvard)
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SPACE-BASED MEASUREMENTS OF HCHO COLUMNSAS
CONSTRAINTS ON VOLATILE ORGANIC COMPOUND (VOC)
EMISSIONS

• VOCs important as
• precursors of tropospheric ozone
• precursors of organic aerosols
• sinks of OH

340 nm
hn (l lt 345 nm), OH
Oxidation (OH, O3, NO3)
VOC
HCHO
lifetime of hours
several steps
Vegetation Anthropogenic Biomass burning
1000 200 100
Tg C yr-1
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RELATING HCHO COLUMNS TO VOC EMISSION
hn (lt345 nm), OH
oxn.
VOCi
HCHO
yield yi
k 0.5 h-1
Emission Ei
smearing, displacement
In absence of horizontal wind, mass balance for
HCHO column WHCHO
Local linear relationship between HCHO and E
but wind smears this local relationship between
WHCHO and Ei depending on the lifetime of the
parent VOC with respect to HCHO production
Isoprene
WHCHO
a-pinene
propane
Distance downwind
100 km
VOC source
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TIME-DEPENDENT HCHO YIELDS FROM VOC OXIDATION
Box model simulations with state-of-science MCM
v3.1 mechanism
methylbutenol
High HCHO signal from isoprene with little
smearing, weak and smeared signal from terpenes
GEOS-Chem yields from isoprene may be too low by
10-40 depending on NOx
Palmer et al, 2006
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HCHO YIELDS FROM ISOPRENE OXIDATION
HCHO vs. isoprene columns in INTEX-A
Sensitivity to peroxide recycling (standard model
assumes recycling)
Ultimate HCHO yield
INTEX-A observations imply a per carbon yield of
0.32 0.1
Palmer et al. 2003, Millet et al. 2006
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RADICAL CHEMISTRY IN UPPER TROPOSPHEREINTEX-A
aircraft data over southeast U.S. (Jul-Aug 04)
OH
O3
HO2
NOx
Black observations by Cohen (NO2), Avery
(ozone), Brune (HO2 and OH) Red standard model
simulation Green model simulation with 4x
lightning
Fixing NOx (and ozone!) results in 3x
overestimate of OH in upper troposphere IF we
could fix OH, the NOx and ozone underestimates
would fix themselves
Hudman et al. (in prep.)
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BrOx CHEMISTRY IN TROPOSPHERE
Yang et al. 2005 global model including
bromocarbon oxidation/photolysis and sea salt
debromination
Satellites observe 0.5-2pptv BrO in excess of
what stratospheric models can explain.
Tropospheric BrO ?
due to Arctic BL spring bloom
Significant consequences for tropospheric ozone
and NOx budgets
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MERCURY IN THE ATMOSPHERE
REACTIVE GASEOUS MERCURY (RGM)
TOTAL GASEOUS MERCURY (TGM)
Hg(II) (gas)
Hg(0) (gas)
Oxidation OH, O3, Br(?)
VERY SOLUBLE
RELATIVELY INSOLUBLE ATMOSPHERIC LIFETIME
ABOUT 1 YEAR TYPICAL LEVELS 1.7 ng m-3
Reduction Photochemical aqueous (?)
Hg(II) (aqueous)
Hg(P) (solid)
LIFETIME DAYS TO WEEKS TYPICAL LEVELS
1-100 pg m-3
DRY AND WET DEPOSITION
EMITTED BY COAL- FIRED POWER PLANTS
ECOSYSTEM INPUTS
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LARGE UNCERTAINTY IN ATMOSPHERIC Hg CHEMISTRY
In standard GEOS-Chem, 80 of Hg(0) oxidation is
by OH 60 of produced Hg(II) is reduced back to
Hg(0) photochemically in clouds
Large discrepancies in reported rates!
(parenthetical reactions not in model)
Deposition
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RAPID CONVERSION OF Hg(0) to Hg(II) IN ARCTIC
SPRINGObservation of Mercury Depletion Events
(MDEs)
Br
Br, OH
1
3
Hg0
HgBr
HgBrX
2
Goodsite et al., EST 2005
T
MDEs correlate with ODEs and reactive halogens
(up to 30pptv BrO).
Spitzbergen Sprovieri et al., EST 2005
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EVIDENCE FOR OXIDATION OF Hg(0) BY Br IN MARINE
BOUNDARY LAYER
Residual diurnal cycle of Hg(0) observed at
Okinawa in April
Consistent with Br release from Br2 or HOBr at
sunrise
Jaffe et al 2005 Selin et al. 2006
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COULD Br BE THE MISSING GLOBAL Hg(0) OXIDANT?
Br mixing ratio (Yang et al., 2005)
Hg0 Lifetime
Global lifetime of Hg(0) against oxidation by Br
0.6 y (range 0.2-1.6 y) Compare to
observational constraint of 1 y for Hg lifetime
against deposition
Holmes et al., GRL 2006