REGIONAL/GLOBAL INTERACTIONS IN ATMOSPHERIC CHEMISTRY

                                                                                                                                                                                       

        

Greenhouse gasesHalocarbonsOzoneAerosolsAcidsNutrients ToxicsSOURCE CONTINENT

REGIONAL ISSUES: - Surface air quality - Ecosystems

GLOBAL ISSUES: - Climate change - Ozone layer - Oxidizing power

GLOBAL ATMOSPHERE

TROPOSPHERIC OZONE AND AEROSOLS MAKE LARGE AND INHOMOGENEOUS CONTRIBUTIONS TO RADIATIVE FORCING

IPCC 2001 contribution from Harvard/GISS/Caltech/UCI unifiedaerosol-chemistry-climate model (CACTUS)

1800-2000 radiative forcing from tropospheric ozoneis less well constrained than implied by IPCC 2001 report

Standard preindustrial simulation:

F = 0.44 W m-2

“Adjusted” preindustrial simulation(lightning and soil NOx decreased,biogenic hydrocarbons increased):

F = 0.80 W m-2

[Mickley et al., 2001]

Ozone+sulfate radiative forcings, 1800-2000(CACTUS model)

Yearly mean values [Mickley et al., 1999]

INTERCONTINENTAL INFLUENCE ON SURFACE OZONE:How much does it contribute to ozone pollution?

NOx

Hydrocarbons Ozone

PAN

Boundary layer(0-2.5 km)

Free tropospherelightningNOx

Stratosphere Ozone

NOx

Hydrocarbons Ozone

PAN Chemical lossDeposition

CONTINENT 1 CONTINENT 2OCEAN

Ozone in U.S. surface air in summer includes a 20-40 ppbv background produced outside the U.S. boundary layer

Regional pollution coordinate

OzoneBackground(“clean air”)

Ozone vs. total nitrogen oxides (NOy) at eastern U.S. sites [Trainer et al., 1993]

Historical records imply a large anthropogenic contribution to the present-day ozone background

Ozone trend at European mountain sites, 1870-1990 [Marenco et al., 1994]

8-h daily maximum ozone probability distribution at rural U.S. sites[Lin et al., 2000]

AIRS data statistics suggest that background ozone in U.S.has increased by ~3 ppbv over past 20 years

1980-1984 1994-1998

1980-1984

1994-1998

The present ozone background is a sizable increment towards violation of air quality standards

0 20 40 60 80 100 120 ppbv

AOT40(seasonal)

NAAQS(8-h avg.)

NAAQS(1-h avg.)

preindustrial presentbackground

Growth of Asian emissions over next decades will increase role of background for ozone air quality in U.S.

109 atoms N cm-2 s-1

AnthropogenicNOx emissions[IPCC, 2001]

2000

2020“Optimistic” IPCCscenario:OECD, U.S. down 20%Asia up 50%

Modeled increase in U.S. surface ozone (ppbv) from tripling of Asian emissions (1985 to 2015)

with other emissions held constant [Jacob et al., 1999]

Rising Asian emissions could offset the benefit of domestic emission controls

Modeled surface ozone change (ppbv) in July for 25% reduction of U.S. NOx and hydrocarbon emissions

with constant Asian emissions (1985) with tripled Asian emissions

Jacob et al. [1999]

Increase in surface ozone from transatlantic transport of N. American and European pollution

[Li et al., 2001]

N.American influenceon Europe

European influenceon N. America

GEOS-CHEM model results, July 1997

GEOS-CHEM: latest generation of global 3-D models of atmospheric chemistry at Harvard

• 1ox1o- 4ox5o horizontal resolution, 20-48 layers in vertical• Assimilated meteorological data from NASA/GEOS, 1988-2001• Recent/current applications:

– Tropospheric ozone : global budget, Asian outflow, U.S., Middle East, N Atlantic, tropics, interannual variability, trends

– Stratospheric ozone: coupling with troposphere– Carbon monoxide: global and regional budgets, interannual

variability– Organics: hydrocarbons, acetone, HCN, CH3I– Aerosols: radionuclides, sulfate, soot, dust, organics

(collaborations with NASA/GSFC, Duke, U. Washington) – Satellite retrievals: formaldehyde, NO2, CO, ozone– Chemical forecasts: TRACE-P, NOAA 2002

APPLICATION OF GEOS-CHEM TO THE ORIGIN OF BACKGROUND OZONE IN U.S. IN SUMMER 1995

[Fiore et al., 2001]

• NASA/GEOS assimilated meteorological data for 1995 • 2ox2.5o horizontal resolution, 26 vertical layers• 120 chemical species (O3-NOx-hydrocarbon chemistry);

aerosol effects on chemistry, radiation • SAMI July 1995 inventory for eastern U.S.

Evaluation with AIRS, SOS, NARSTO-NE observations

SUMMER 1995 AFTERNOON OZONEIN SURFACE AIR OVER THE U.S.

AIRS observations

GEOS-CHEM(r2 = 0.4, bias=3 ppbv)

FREQUENCY DISTRIBUTION OF SURFACE p.m. O3

IN WESTERN MASSACHUSETTS IN SUMMER 1995

Observations(squares, triangles)

Model(crosses) Air quality

standard

MEAN AFTERNOON OZONE BACKGROUNDIN MODEL, SUMMER 1995

Background is tagged as ozone produced outside the N. American boundary layer (surface-700 hPa)

OZONE BACKGROUND IS DEPLETED DURING REGIONAL POLLUTION EPISODES

(due to stagnation, short O3 lifetime)

Background(clean conditions)

O3 vs. (NOy-NOx) At Harvard Forest, Massachusetts

Background(pollution episodes)

FREQUENCY DISTRIBUTION OF AFTERNOON BACKGROUND OZONE CONCENTRATIONS

IN U.S. SURFACE AIR IN SUMMER 1995 (model)summer ensemble vs. pollution episodes

Convection upwindoccasionally results inhigh background during pollution episodes

Convection upwind can result in high background contributions to ozone pollution episodes

Time, days0 1 2 3

Subsidence inversion

Boundarylayer

Free troposphere

Ozonedowndraft

fast ozoneproduction

> 50 ppbv day-1

Convectivecloud

Ozone pollutionepisode

ASIAN/EUROPEAN POLLUTION ENHANCEMENTOF BACKGROUND OZONE IN U.S.

Mean model values, summer 1995 (4ox5o resolution)

“Natural” background(no anthropogenicemissions of NOx

or NMHCs anywhere,but present-day CH4)

Asian/Europeananthropogenicenhancement abovenatural background (no anthropogenicemissions in North America)

RANGE OF ASIAN/EUROPEAN POLLUTION OZONE ENHANCEMENTS OVER THE UNITED STATES

ensemble of model results, summer 1995

Max enhancements(up to 14 ppbv)under moderatelypolluted conditions(50-70 ppbv O3)associated with recent convection

MAJOR CONCERNIF OZONE STANDARDWERE TO DECREASETO 40 or 60 PPBV

CONCLUSIONS

• Surface ozone in U.S. in summer includes a 20-40 ppbv background originating from outside North America

• Present-day Asian emissions enhance this background by 3-7 ppbv (up to 14 ppbv)

• Asian influence on surface ozone in U.S. is highest under moderately polluted conditions (50-70 ppbv), less during acute pollution episodes (> 80 ppbv) or clean conditions

(< 40 ppbv)

• Importance of background will increase in the future due to rise in Asian emissions, lower metrics for ozone standard.

FUTURE WORK• EPA/Harvard modeling collaboration

– Examine ozone perturbations from intercontinental transport for future scenarios and sensitivity studies

– Examine intercontinental transport of aerosols, ozone-aerosols coupling– Couple Models-3 and GEOS-CHEM to extend the nested-model capability of

Models-3 to the global scale.

• Analysis of aircraft data directed at intercontinental transport: – TRACE-P, spring 2001 (Asian outflow)– NOAA/ITCT, spring 2002 (North American inflow)– INTEX/NA, summer 2004 (North American outflow/inflow)

• Assimilation of satellite observations into global models– Use global mapping capabilities from satellites to test model simulations of

intercontinental transport for CO, ozone, aerosols