CHEMISTRY-CLIMATE INTERACTIONS: science questions, science needs Daniel J. Jacob THE BROAD QUESTIONS: How do chemical processes in the troposphere affect climate change? How does climate change affect air quality? Focus on three chemical themes: (1) organic aerosols, (2) radicals, (3) tropospheric ozone

SECONDARY ORGANIC AEROSOL (SOA): underestimated component of climate forcing? simulated/observed ratios from recent measurement campaigns Volkamer et al. [2006] Current model parameterizations based on gas-aerosol thermodynamic partitioning of semi-volatile products of VOC oxidation grossly underestimate OC aerosol concentrations in aged air

WSOC AEROSOL OVER EASTERN U.S. IN ITCT-2K4 Observations GEOS-Chem Total Fires Fossil fuel Biogenic SO x WSOC (R. Weber) Model OC attribution Observed free tropospheric concentrations are lower than in ACE-Asia; model is only 25% too low in the mean… …but is incapable of reproducing observed variability in boundary layer (r 2 = 0.11) or free troposphere (r 2 = 0.05) Observed free tropospheric WSOC has significant correlation (r 2 ~ 0.3) with methanol combined with sulfate, nitrate, or toluene; suggests cloud production mechanism and combined bio-anthro source Heald et al. [2006]

EFFECT OF GLOBAL CHANGE ON ANNUAL MEAN ORGANIC CARBON (OC) AEROSOL CONCENTRATIONS (  g m -3 ) Wu et al. [2007] Climate change effect is mainly through biogenic SOA and is small because of compensating factors (higher biogenic VOCs, higher volatility) 2000 conditions: OC,  g m -3  2000 emissions & 2050 climate)

WILDFIRES: A GROWING OC AEROSOL SOURCE S. California fire plumes, Oct Total carbonaceous (TC) aerosol averaged over all contiguous U.S. IMPROVE sites ~100 IMPROVE sites nationwide Interannual variability in organic aerosol is largely determined by wildfires Open fires contribute about 25% of annual mean PM 2.5 in the western U.S., 10% in the east Dominant contributions from western U.S. fires (in the west), Canadian fires (in the northeast), prescribed fires (in the southeast) U.S. fire source expected to increase over the next decades Park et al. [2007] Secondaryformation?

HOW DO WE PROGRESS ON ORGANIC AEROSOL? Improve OC aerosol characterization –Intercomparison of different methods aboard aircraft for range of conditions; test measurements of mass concentrations, chemical speciation –Characterize mixing state, hygroscopicity, optical properties –Validate/interpret satellite AOD observations in high-OC regions Better understand relationship to precursors –Continental boundary layer mapping for polluted vs. clean vegetated areas –Lagrangian sampling of pollution and fire plumes over ocean, in free troposphere. –Payload should include VOCs, (di)carbonyls, carboxylic acids that might be involved in SOA production

HO x RADICALS: DRIVERS OF METHANE SINK AND OF AEROSOL AND OZONE FORMATION Hudman et al. [2007] Large and inconsistent differences between models and observations discourage analyses of factors controlling HO x concentrations Simulated vs. observed concentrations during INTEX-A (summer 2004) (Brune, Heikes, Fried, Huey)

RADICAL BROMINE CHEMISTRY IN TROPOSPHERE due to Arctic BL spring bloom GOME satellite instrument observes pptv BrO in excess of what stratospheric models can explain. Large enhancement seen in polar spring; confined to boundary layer or larger extent? Tropospheric BrO ? Important implications for tropospheric HO x, ozone, NO x, and mercury Tropospheric BrO from OMI March 11, 2005 (K.V. Chance)

THE MYSTERY OF OXYGENATED VOCs Methanol vertical profiles over South Pacific (PEM-Tropics B) Methanol, ppbv model atmospheric source observed (Singh) Jacob et al. [2005] GEOS-Chem Models cannot reproduce background observations of methanol, acetone (200 pptv), acetaldehyde (~100 pptv) in remote air…Could there be a missing “VOC soup” driving organic chemistry in the remote troposphere?

HOW DO WE PROGRESS ON TROPOSPHERIC RADICALS? Improve and validate aircraft instrumentation –Intercompare different HO x measurement techniques; –Develop measurement capability for CH 3 O 2 –Develop measurement capabilities for BrO and reservoir species Interpret observed variability of HO x, BrO radical concentrations in relationship to reservoirs, NO x, other variables –Aircraft observations over wide range of conditions; –Begin with box models including max observational constraints, graduate to 3-D models accounting for transport of reservoirs

TROPOSPHERIC OZONE: 3 rd ANTHROPOGENIC GREENHOUSE GAS Model values for preindustrial ozone yield radiative forcing  F = 0.4 W m -2 (IPCC) } Models fail to reproduce observed ozone trends over 20 th century or over past decades; implies uncertainty in radiative forcing, hemispheric pollution Observations at European mountain sites [Marenco et al., 1994]: imply  F = 0.8 W m -2 [Mickley et al., 2001]

GOME JJA 1997 tropospheric columns (Dobson Units) SATELLITE OZONE RETRIEVALS: WHO’S RIGHT? Also long-standing model problem of overestimate vs. ondes over South Asia… GEOS-Chem model maximum over Middle East [Li et al., 2001]: is it real? IR emission measurement from TESUV backscatter measurement from GOME Liu et al., 2006 Zhang et al., 2006

MAJOR SOURCE OF NO x FROM MID-LATITUDES LIGHTNING Observations and model simulations from ICARTT aircraft campaign over eastern N. America in summer 2004 Observations GEOS-Chem model (standard) GEOS-Chem model (lightningx4) Observed flash frequency …suggests great sensitivity of ozone to climate change Hudman et al. [2007] implies 500 moles NO x per flash

OMI HCHO TESTS ISOPRENE EMISSION INVENTORIES Isoprene emissions from the MEGAN biogenic emission inventory (summer 2006) HCHO columns from OMI satellite instrument (summer 2006) ? OMI indicates overestimate of broadleaf deciduous source in MEGAN; no support for “isoprene volcano” in the Ozarks Millet et al. [2006, 2007] Individual VOC contributions to HCHO column (INTEX-A)

USE OZONE-TEMPERATURE CORRELATION TO ESTIMATE EFFECT OF CLIMATE CHANGE ON AIR QUALITY Probability of max 8-h O 3 > 84 ppbv vs. daily max. temperature Projected T change for northeast U.S. in simulated with ensemble of GCMs for different scenarios [IPCC, 2007]  T = 3K Probability Temperature, K Probability of exceedance doubles By 2025,  T = 1-3 K depending on model and scenario; use statistical approach at right to infer increased probability of ozone exceedance for a given region or city assuming nothing else changes. Effect is large! Lin et al. [2007] Lin et al. [2001] Northeast Los Angeles Southeast

CHANGES IN SUMMER MEAN 8-h AVG. DAILY MAXMUM OZONE FROM CLIMATE CHANGE 2000 conditions ( ppb)  2000 emissions & 2050 climate) Wu et al. [2007] Isoprene emis +30%  Δ(O 3 ) Increase in midwest and northeast (up to 10 ppbv in pollution episodes) No change in southeast where isoprene nitrates are an important sink for NO x ; controversial! GISS/GEOS-Chem model results

HOW DO WE PROGRESS ON TROPOSPHERIC OZONE? Validate and improve satellite observations –validate TES and OMI over tropical/subtropical continents –assimilate TES+OMI+other data including precursors for determination of inconsistencies –develop new passive instrumentation for UV+IR (+ Chappuis?), active instrumentation Better define lightning NO x source using satellite and aircraft – need further development/validation of HNO 3 satellite retrievals –Focus on tropics – leverage on new lighning detection networks Better define isoprene source using satellite and aircraft –Focus on tropics – use aircraft to measure VOC emission fluxes and determine local relationship to HCHO (photochemistry) Better understand factors controlling sources, chemistry of biogenic VOCs –Sensitivity to environmental conditions (satellites, towers) –Atmospheric chemistry of organic nitrates and peroxides (aricraft, towers) Improve understanding of stratosphere-troposphere exchange –Satellite observations with high vertical resolution (HIRDLS or follow-on)