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EPA Science Advisory BoardFirst National Science Workshop on Environmental Protection
Emerging Scientific Topics: Transboundary Air Pollutants
Continental-Scale Transport of Air Pollutants
Rudolf HusarWashington University, St. Louis, MO
December 11, 2003Ronald Reagan Building and International Trade Center
1300 Pennsylvania Avenue, NWWashington, DC
The BIG PICTURE
How do humans perturb the atmospheric composition?
Opportunities & Challenges
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
NASA Astronaut Limb Photo
Troposphere
Stratosphere
Boundary Layer
Aerosol Layers
Clouds
Particulate Matter and Ozone – Key Pollutants
• PM Episodic impact
• Ozone Raises the background
• Anthropogenic - Natural – Anthropogenic steady, seasonal
– Mostly sporadic, seasonal
What is Particulate Matter and How does it Vary?
•What is Particulate Matter?
•How Does PM Vary?
•The Influence of Emissions, Dilution and Transformations
•Resource Links
Contact: Rudolf Husar, [email protected]
Aerosol Size Distribution and Morphology
Purposes of the illustration:1. Size spectra over 4 decades, modes
2. Particle shapes, electron micrographs
3. Chemical composition by size
Properties of Particulate Matter
•Physical, Chemical and Optical Properties
•Size Range of Particulate Matter
•Mass Distribution of PM vs. Size: PM10, PM2.5
•Fine and Coarse Particles
•Fine Particles - PM2.5
•Coarse Particle Fraction - PM10-PM2.5
•Chemical Composition of PM vs. Size
•Optical Properties of PM
•Resource Links Contact: Rudolf Husar, [email protected]
Major Biogeochemical Processes Producing Aerosols
Windblown Dust Volcanic Emissions
Industrial Aerosols
What is the magnitude of the anthropogenic perturbation of natural processes?
On global scale dust, smoke dominate the aerosol pattern.
Industrial aerosols dominate regional hot-spots
Smoke from Fires
Regional Haze Goal: Attain natural conditions by 2064
Industrial Sulfur Emission Density
The regional hot-spots for industrial sulfur emissions are in
E. North America,
Europe and
E. Asia
US SOx Emission
MODIS AOT, 2002 MODIS Team
Features of Global Smoke Emissions
ATSR Fire Locations 1993
MISR Seasonal AOT (MISR Team)Major smoke emission regions by season
Pattern of Fires over N. AmericaThe number of ATSR satellite-observed fires peaks in
warm seasonFire onset and smoke amount is unpredictable
Fire Pixel Count:
Western US
North America
May 15, 1998
• Fire locations detected by the Defense Meteorological Satellite Program (DMSP) sensor.
• Smoke is detected by SeaWiFS and TOMS (green) satellites and surface visibility data, Bext
Smoke from Central American Fires
• The smoke plume extends from Guatemala to Hudson May in Canada
• The Bext values indicate that the smoke is present at the surface
Smoke Aerosol and Ozone During the Smoke Episode – Inverse Relationship
The surface ozone is generally depressed under the smoke cloud
Extinction Coefficient (visibility)
Surface Ozone
May-June 2003 Siberian Fires
Global Transport of Siberian Smoke
Aircraft Detection of Siberian Forrest Smoke near Seattle, WA
Jaffe et. al., 2003
The Asian Dust Event of April 1998
On April 19, 1998 a major dust storm occurred over the Gobi Desert
The dust cloud was seen by SeaWiFS, TOMS, GMS, AVHRR satellites
The transport of the dust cloud was followed on-line by an an ad-hoc international group
China
Mongolia
Korea
Asian Dust Cloud over N. America
On April 27, the dust cloud arrived in North America.
Regional average PM10 concentrations increased to 65 g/m3
In Washington State, PM10 concentrations exceeded 100 g/m3
Asian Dust 100 g/m3
Hourly PM10
Origin of Fine Dust Events over the US
Gobi dust in springSahara in summer
Fine dust events over the US are mainly from intercontinental transport
Daily Average Concentration over the US
Dust is seasonal with noise
Random short spikes added
Sulfate is seasonal with noiseNoise is by synoptic weather
VIEWS Aerosol Chemistry Database
Sahara and Local Dust Apportionment: Annual and July
• The maximum annual Sahara dust contribution is about 1 g.m3
• In Florida, the local and Sahara dust contributions are about equal but at Big Bend, the Sahara contribution is < 25%.
The Sahara and Local dust was apportioned based on their respective source profiles.
• In July the Sahara dust contributions are 4-8 g.m3
• Throughout the Southeast, the Sahara dust exceeds the local source contributions by w wide margin (factor of 2-4)
AnnualJuly
Supporting Evidence: Transport Analysis
Satellite data (e.g. SeaWiFS) show Sahara Dust reaching Gulf of Mexico and
entering the continent.
The air masses arrive to Big Bend, TX form the east (July) and from the west
(April)
Seasonal Fine Aerosol Composition, E. USUpper Buffalo Smoky Mtn
Everglades, FLBig Bend, TX
Sahara PM10 Events over Eastern USMuch previous work by Prospero, Cahill, Malm, Scanning the AIRS PM10 and IMPROVE chemical
databases several regional-scale PM10 episodes over the Gulf Coast (> 80 ug/m3) that can be attributed to Sahara.
June 30, 1993
The highest July, Eastern US, 90th percentile PM10 occurs over the Gulf Coast ( > 80 ug/m3)
Sahara dust is the dominant contributor to peak July PM10 levels.
July 5, 1992
June 21 1997
Local, Regional, Global Pollution
Before 1950s:
LocalSmoke, Fly ash
Post- 2000s:
GlobalGlobal Change
1970s-1990s:
RegionalAcid Rain, Haze
The Climates of North America ( Based on Bryson and Hare, 1974)
What kind of neighborhood is this anyway?
May 9, 1998 A Really Bad Aerosol Day for N. America
Asian Smoke
C. American Smoke
Canada Smoke
Cooperation: Monitoring, Impact, Actions
• International– North American transboundary transport
• Inter-Agency– EPA: Monitoring, impact assessment and management actions
– NASA: Satellite data and tools for documentation of transport
– NOAA: Weather, satellite, model
• Inter-Disciplinary
Seasonal cycle in mean afternoon surface O3 over the US
Based 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 in prep.
