EPA Science Advisory Board workshopEmerging Scientific Topics

Air Pollution Control: Transboundary Air PollutantsDecember 11, 2003

Russell Dickerson, Univ. Maryland

Thunderstorms convert local air pollution problems into global atmospheric chemistry problems.

Tropospheric Ozone Formation

I. NOx is the limiting reagent outside urban areas.

II. Efficiency of ozone production falls as NOx concentration increases.

III. Lifetimes, wind speeds, and photolysis rates all higher aloft.

Atmospheric Residence Time Increases with Height

• Fine Particle residence time in the boundary layer, is 3-5 days.

• Residence time in the free troposphere is weeks and the transport is hemispheric

• Photo prepared by R. Husar, Washington Univ.

NASA Astronaut Limb Photo

Troposphere

Stratosphere

Boundary Layer

Aerosol Layers

Clouds

AEROCE Finding: Transport of pollutants from North America to the North Atlantic via linked

cold fronts (Prados, 2000)

Aircraft observations show how cold fronts lift and transport air pollutants to the east. Colored line shows King Air flight track.

TOMS tropospheric ozone (Thompson & Hudson)

Remote sensing of Ozone Surface network TOMS

Seasonal cycle in mean afternoon surface O3 over the USBased on the Harvard global model and surface observations

Regional pollution: 10-30 ppbv

Hemisph. pollution: 5-15 ppbv

Natural ozone: 15-25 ppbv

Stratospheric ozone: 0-10 ppbv

Fiore et al., JGR 2003.

US Trend: Peaks are falling but bottom is coming up.

The ambient EC concentration decreased ~50% in 11 yr.

INDOEX, 1999

INDOEX: Indian Ocean Experiment

Indian Today, 1996.

Mean Aerosol Optical Depth over INDOEX region from Dec 2001 to May 2003 from MODIS (Ramanathan &

Ramana, Environ. Managers, Dec. 2003).

Global Fossil Fuel Black Carbon* Emissions(Cooke et al.,1999; Penner et al., 1993; Dickerson et al., 2002)

Region BC Emissions Tg yr-1

W. Europe 0.58

Eastern Europe 0.68

Africa 0.17

N. America 0.49

C. & S. America 0.26

Former USSR 0.69

China & Oceania 1.18

Rest of Asia 2.00

Total fossil fuel 6.17

Biomass Burning 5.97

*Major greenhouse substance.

• South Asia emits large quantities of VOC’s and POM, but little NOx.

• Little ozone is observed over India or the Northern Indian Ocean. VOC/NOx ratio too high(?).

• This could change as vehicle fleet shifts from 2-stroke to 4-stroke engines.

Nitrogen DepositionPast and Present

mg N/m2/yr

1860 1993

500020001000 750 500 250 100 50 25 5

Galloway et al., 2003

“A systems approach integrating both animal and crop productions is necessary to evaluate air emissions…. “

NRC 2003

Summary & Conclusions

• Nonlinearities in chemistry and longer lifetimes of trace gases and aerosols in the free troposphere promote long-range transport.

• Much of the growth in emissions in the coming decades will come from the developing world.

• Asia is different from North America:Organic aerosol & soot from biofuels & 2-stroke engines.

• Conversion to high-tech combustion could lead to more ozone.

• We need interdisciplinary and international colaboration.

The End.

Modeled Carbon Monoxide TRACE-P/ACE-Asia

Pickering et al., 2002

Forecasts & Observations of Air Pollution

Over the Mid Atlantic

Shot from UMD Research AircraftDickerson, Doddridge, Piety et al.

Impactor Sample from INDOEX

Global distribution of AOD (550 nm) for April & May, 2001 and 2002; from MODIS. (Ramanathan and Ramana, 2003).

Cruise Track and Air Flow During INDOEX 1999

Lo n g itu d e

4 0 E 6 0 E 8 0 E

2 0 S

0

2 0 N

1 0 0 E

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C ru ise tra c k o f R. H. Bro wn

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