CHEMISTRY-CLIMATE INTERACTIONS:CHEMISTRY-CLIMATE INTERACTIONS:science questions, science needsscience questions, science needs

Daniel J. JacobDaniel 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):SECONDARY ORGANIC AEROSOL (SOA):underestimated component of climate forcing?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 underestimateOC aerosol concentrations in aged air

WSOC AEROSOL OVER EASTERN U.S. IN ITCT-2K4WSOC AEROSOL OVER EASTERN U.S. IN ITCT-2K4

ObservationsGEOS-Chem

TotalFiresFossil fuelBiogenic

SOx 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 (r2 = 0.11) or free troposphere (r2 = 0.05)• Observed free tropospheric WSOC has significant correlation (r2 ~ 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 2000-2050 GLOBAL CHANGE ON ANNUAL MEAN EFFECT OF 2000-2050 GLOBAL CHANGE ON ANNUAL MEAN ORGANIC CARBON (OC) AEROSOL CONCENTRATIONS (ORGANIC CARBON (OC) AEROSOL CONCENTRATIONS (g mg m-3-3))

Wu et al. [2007]

Climate change effect is mainly through biogenic SOA and is smallbecause of compensating factors (higher biogenic VOCs, higher volatility)

2000 conditions: OC, g m-3 2000 emissions & 2050 climate)

WILDFIRES: A GROWING OC AEROSOL SOURCEWILDFIRES: A GROWING OC AEROSOL SOURCES. California fire plumes,Oct. 25 2004

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 PM2.5 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]

SecondarySecondaryformation?formation?

HOW DO WE PROGRESS ON ORGANIC AEROSOL?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

HOHOxx RADICALS: DRIVERS OF METHANE SINK AND RADICALS: DRIVERS OF METHANE SINK AND

OF AEROSOL AND OZONE FORMATIONOF AEROSOL AND OZONE FORMATION

Hudman et al. [2007]

Large and inconsistent differences between models and observations discourage analyses of factors controlling HOx concentrations

Simulated vs. observed concentrations during INTEX-A (summer 2004)

(Brune, Heikes, Fried, Huey)

RADICAL BROMINE CHEMISTRY IN TROPOSPHERERADICAL BROMINE CHEMISTRY IN TROPOSPHERE

due to Arctic BL spring bloom

GOME satellite instrument observes 0.5-2pptv 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 HOx, ozone, NOx, and mercury

Tropospheric BrO from OMIMarch 11, 2005 (K.V. Chance)

THE MYSTERY OF OXYGENATED VOCsTHE MYSTERY OF OXYGENATED VOCsMethanol vertical profiles over South Pacific (PEM-Tropics B)

0 0.6 1.2 1.8 2.4 3 0 0.6 1.2 1.8 2.4 3 0 0.6 1.2 1.8 2.4 3Methanol, 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?HOW DO WE PROGRESS ON TROPOSPHERIC RADICALS?

• Improve and validate aircraft instrumentation

– Intercompare different HOx measurement techniques;

– Develop measurement capability for CH3O2

– Develop measurement capabilities for BrO and reservoir species

• Interpret observed variability of HOx, BrO radical concentrations in relationship to reservoirs, NOx, 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: TROPOSPHERIC OZONE: 33rdrd ANTHROPOGENIC GREENHOUSE GAS ANTHROPOGENIC GREENHOUSE GAS

Model values forpreindustrial ozone yield radiative forcingF = 0.4 W m-2 (IPCC)

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Models fail to reproduce observed ozone trends over 20th 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?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 TES UV backscatter measurement from GOME

Liu et al., 2006

Zhang et al., 2006

MAJOR SOURCE OF NOMAJOR SOURCE OF NOxx FROM MID-LATITUDES LIGHTNING FROM MID-LATITUDES LIGHTNINGObservations and model simulations from ICARTT aircraft campaign

over eastern N. America in summer 2004

ObservationsGEOS-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 NOx per flash

OMI HCHO TESTS ISOPRENE EMISSION INVENTORIES 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 USE OZONE-TEMPERATURE CORRELATION TO ESTIMATE EFFECT OF CLIMATE CHANGE ON AIR QUALITYEFFECT OF CLIMATE CHANGE ON AIR QUALITY

Probability of max 8-h O3 > 84 ppbvvs. daily max. temperature

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1900 1950 2000 2050 2100

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mer

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CCSM 1 PCM 1CCSM 2 PCM 2CCSM 3 PCM 3CCSM 4 HadCM3ECHAM 1 GFDL 0ECHAM 2 GFDL 1ECHAM 3 GISS

Projected T change for northeast U.S. in 2000-2100 simulated with ensemble of GCMs for different scenarios [IPCC, 2007]

T = 3K

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bab

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Temperature, K

Probabilityof exceedancedoubles

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]

NortheastLos AngelesSoutheast

CHANGES IN SUMMER MEAN 8-h AVG. DAILY MAXMUM OZONE CHANGES IN SUMMER MEAN 8-h AVG. DAILY MAXMUM OZONE FROM 2000-2050 CLIMATE CHANGE FROM 2000-2050 CLIMATE CHANGE

2000 conditions ( ppb) 2000 emissions & 2050 climate)

Wu et al. [2007]

Isoprene emis +30% Δ(O3)

• Increase in midwest and northeast(up to 10 ppbv in pollution episodes)• No change in southeast where isoprene nitrates are an important sink for NOx; controversial!

GISS/GEOS-Chem model results

HOW DO WE PROGRESS ON TROPOSPHERIC OZONE?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 NOx source using satellite and aircraft

– need further development/validation of HNO3 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)

EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATIONEFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION

Pollution episodes double in duration in 2050 climate due to decreasing frequency of cyclones ventilating the eastern U.S; this decrease is an expected consequence of greenhouse warming.

GISS GCM 2’ simulations for 2050 vs. present-day climate using pollution tracers with constant emissions

Mickley et al. [2004]

2045-2052

1995-2002

summer

Mid-latitudes cyclones tracking across southern Canada are the main drivers of northern U.S. ventilation

Northeast U.S.CO pollution tracer

Clean airsweepsbehind cold front

Sunday night’s weather map