1. 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

2. 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 species…by 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

3. OUR FIRST ORGANIC CARBON (OC) SIMULATION FOR THE UNITED STATES
IMPROVE obs (1998)
annual
Park et al. [2003]
U.S. source:
2.7 Tg yr-1
10%
terpenes

4. FIRST MASS CONCENTRATION MEASUREMENTS OF OC AEROSOLS IN FREE TROPOSPHERE
ACE-Asia aircraft data over Japan (April-May 2001)
Observed
(Russell)
Observed (Huebert)
GEOS-Chem
(Chung & Seinfeld
for SOA)
Chung and Seinfeld scheme:
OC/sulfate ratio
Observations show 1-3 mg m-3 background;
model too low by factor
Heald et al. [2005]

5. 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.

6. MODEL OC AEROSOL SOURCES DURING ITCT-2K4
~10% yield
~2% yield
Large fires in Alaska
and NW Canada:
60% of fire emissions
released above 2 km
(pyro-convection)
Heald et al., in prep.

7. ITCT-2K4 OC AEROSOL: VERTICAL PROFILES
Observations
Model
Total
Biomass burning
Anthropogenic
Biogenic SOA
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.

8. CORRELATION OF OBSERVED FREE TROPOSPHERIC WSOC WITH OTHER CHEMICAL VARIABLES IN ITCT-2K4
No single variable gives R > 0.37, but toluene bivariate correlations with
sulfate, acetic acid, and HNO3 give R > 0.7. No correlation with isoprene oxidation products
Suggest aqueous-phase mechanism involving aromatics
Heald et al., in prep.

9. ALTERNATE MECHANISM FOR SOA FORMATION: AQUEOUS-PHASE 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]

10. MODEL REPRESENTATION OF AQUEOUS-PHASE SOA FORMATION USING REACTION PROBABILITY g APPLIED TO GLYOXAL
Liggio et al. [2005]

11. 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

12. OXYGENATED VOCs OVER TROPICAL PACIFIC (PEM-TROPICS B DATA)SH
Singh et al. [2001]
Methanol and acetone are
the principal contributors NH

13. 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
<1 (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)
Urban:
4 (3-8)
Biomass burning:
9 (6-13)
Biofuels: 3
Plant decay:
23 (13-20)
Jacob et al. [2005]

14. SIMULATED METHANOL CONCENTRATIONS IN SURFACE AIR
Representative observations
In ppbv [Heikes et al., 2002]:
Urban: 20 (<1-47)
Forests: 10 (1-37)
Grasslands: 6 (4-9)
Cont. background: 2 (1-4)
NH oceans: 0.9 ( )
Tropics: obs model
Rondonia
Costa Rica
Jacob et al. [2005]

15. METHANOL VERTICAL PROFILES OVER S. PACIFIC
Methanol, ppbv
model atmospheric source
obs. From
H.B. Singh
Could the atmospheric source from CH3O2 + CH3O2 be underestimated?
HO2
CH3OOH
~ 70%
In model over S. Pacific, OH NO
CH4
CH3O2
HCHO
~ 20%
CH3O2
0.6 CH3OH +…
5-10%
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]

16. GLOBAL GEOS-CHEM BUDGET OF ACETONE (Tg yr-1) from Jacob et al
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, O3 OH
terpenes
MBO
7 (3-11) 27 37
Dry dep. (land) : 9 12
Ocean
uptake:
14 19
Ocean
source:
27 (21-33)
microbes
DOC+hv
Urban:
1 (1-2)
Vegetation:
33 (22-42)
Biomass burning:
5 (3-7)
Plant decay:
2 (-3 - 7)

17. a priori sources/sinks; c2 = 1.3 Optimized sources/sinks
OCEANIC SOURCE OF ACETONE IN MODEL NEEDED TO MATCH OBSERVATIONS OVER S. PACIFIC
from Jacob et al. [2002]
obs from Solberg et al.
[1996]
obs. From
H.B. Singh
a priori sources/sinks; c2 = 1.3
Optimized sources/sinks
(including “microbial” ocean sink,
photochemical ocean source); c2 = 0.39

18. …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]
Observed
Model

19. CORRELATION OF ACETONE WITH TRACERS OF SOURCES IN ASIAN OUTFLOW (TRACE-P DATA)
Multiple regression:
Propane source
Continental
source
Acetone = b0
+ b1 [Ethane]
+ b2 [HCN]
+ b3 [Methanol]
Acetone [pptv]
Acetone [pptv]
Intercept = 200 pptv
Ethane [pptv]
CO [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?
HCN [pptv]
Methanol [pptv]
Tzung-May Fu (Harvard)

20. HCHO COLUMN DATA FROM OMI SATELLITE INSTRUMENT
July 2005
Thomas Kurosu (Harvard/SAO) and Dylan Millet (Harvard)

21. SPACE-BASED MEASUREMENTS OF HCHO COLUMNS AS 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 < 345 nm), OH
Oxidation (OH, O3, NO3)
VOC
HCHO
lifetime of hours
several steps
Vegetation Anthropogenic Biomass burning
~ ~ ~100 Tg C yr-1

22. RELATING HCHO COLUMNS TO VOC EMISSION
oxn.
hn (<345 nm), OH
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
100 km
Distance downwind
VOC source

23. 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]

24. HCHO YIELDS FROM ISOPRENE OXIDATION
Sensitivity to peroxide recycling
(standard model assumes recycling)
HCHO vs. isoprene columns
in INTEX-A
observed
WHCHO, 1016 cm-2
WISOP, 1016 cm-2
m = 3.3
m = 3.5
GEOS-Chem
Ultimate
HCHO yield
INTEX-A observations imply a per carbon yield of ± 0.1
Palmer et al. [2003], Millet et al. [2006]

25. RADICAL CHEMISTRY IN UPPER TROPOSPHERE: INTEX-A aircraft data over southeast U.S. (Jul-Aug 04)
NOx O3
HO2 OH
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.)

26. 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

27. MERCURY IN THE ATMOSPHERE
REACTIVE GASEOUS
MERCURY (RGM)
TOTAL GASEOUS MERCURY (TGM)
Hg(II)
(gas)
Hg(0)
(gas)
Oxidation
OH, O3, Br(?)
RELATIVELY INSOLUBLE
ATMOSPHERIC LIFETIME:
ABOUT 1 YEAR
TYPICAL LEVELS:
1.7 ng m-3
VERY
SOLUBLE
Reduction
Photochemical aqueous (?)
Hg(II)
(aqueous)
Hg(P)
(solid)
LIFETIME: DAYS TO WEEKS
TYPICAL LEVELS: pg m-3
DRY AND WET DEPOSITION
EMITTED BY COAL-
FIRED POWER PLANTS
ECOSYSTEM INPUTS

28. 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!
8.7(±2.8) x Sommar et al., AE 2001
9.0(±1.3) x Pal & Ariya, ES&T 2004
much slower Calvert & Lindberg, AE 2005
[cm3 s-1]
(parenthetical reactions not in model)
Deposition
3(±2) x Hall, WASP 1995
1.7 x Iverfeldt & Lindqvist, AE 198
[cm3 s-1]

29. RAPID CONVERSION OF Hg(0) to Hg(II) IN ARCTIC SPRING Observation of Mercury Depletion Events (MDEs)Br
Br, OH 1 3
Hg0
HgBr
HgBrX 2
Goodsite et al., ES&T 2005 T
MDEs correlate with ODEs and reactive halogens (up to 30pptv BrO).
Spitzbergen: Sprovieri et al., ES&T 2005

30. EVIDENCE FOR OXIDATION OF Hg(0) BY Br IN MARINE BOUNDARY LAYER
Residual diurnal cycle of Hg(0) observed at Okinawa in April
Observations
GEOS-Chem (OH,O3)
Consistent with Br release from
Br2 or HOBr at sunrise
Jaffe et al [2005]; Selin et al. [2006]

31. 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 y);
Compare to observational constraint of ~1 y for Hg lifetime against deposition
Holmes et al., GRL 2006