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

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

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

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 10-100 Heald et al. [2005]

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.

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.

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.

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.

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]

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

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

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

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]

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 (0.3-1.4) Tropics: obs model Rondonia 1-6 10 Costa Rica 2.2 2.1 Jacob et al. [2005]

METHANOL VERTICAL PROFILES OVER S. PACIFIC 0 0.6 1.2 1.8 2.4 3 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]

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)

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

…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

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)

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

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 ~1000 ~200 ~100 Tg C yr-1

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

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]

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 0.32 ± 0.1 Palmer et al. [2003], Millet et al. [2006]

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.)

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

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: 1-100 pg m-3 DRY AND WET DEPOSITION EMITTED BY COAL- FIRED POWER PLANTS ECOSYSTEM INPUTS

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 10-14 Sommar et al., AE 2001 9.0(±1.3) x 10-14 Pal & Ariya, ES&T 2004 much slower Calvert & Lindberg, AE 2005 [cm3 s-1] (parenthetical reactions not in model) Deposition 3(±2) x 10-20 Hall, WASP 1995 1.7 x 10-18 Iverfeldt & Lindqvist, AE 198 [cm3 s-1]

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

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]

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