1. Springtime Airmass Transport Pathways to the US Prepared by: Bret A. Schichtel and Rudolf B. Husar CAPITA CAPITA,Washington University Saint Louis, Missouri 63130 Submitted to: Chris Saint, Project Officer Cooperative Agreement No. CR 825211 January 7, 2000

2. Introduction Anthropogenic and natural pollutants generated in one country are regularly transported to other countries adding to their air quality burden. On the average, transboundary pollutants transport to the US small but favorable emission and transport conditions may cause transport episodes. This work begins to assess the transboundary transport to the US by backward airmass histories during the Spring season of 1999. This work complements the companion analysis “Modeling the Episodic Transport of Air Pollutants from Asia to North America” by Hanna et al., 1999Modeling the Episodic Transport of Air Pollutants from Asia to North America

3. Residence Time Analysis Backtrajectories are aggregated by counting the hours each ‘particle’ resided in a grid cell. Back trajectories to Seattle, WA on 3/27/99 overlaid on a grid The ‘residence time’, i.e. hours the Seattle, WA back trajectories resided over each grid cell

4. US Receptor Sites Ten day backward airmass histories for 9 receptor sites were calculated for February-April 1999. Receptor SiteLatitudeLongitude Seattle, WA47.6122.33 San Francisco, CA37.78122.42 San Diego, CA32.72117.15 Minneapolis, MN44.9893.27 St. Louis, MO38.6290.2 San Antonio, TX29.4298.5 Boston, MA42.3771.07 Norfolk, VA36.8576.28 Miami, FL25.7880.18 The airmass histories were calculated using the CAPITA Monte Carlo Model driven by the FNL global meteorological data. This system was previously validated for hemispheric transport by simulating the April 1998 Chinese Dust Event.CAPITA Monte Carlo Model FNL global meteorological dataApril 1998 Chinese Dust Event Each airmass history is composed of 15 trajectories which are tracked at two hour time increments back in time. Approximately, 12,000 trajectories per receptor were calculated The back-trajectory starting heights are within the mixing layer. Temperature, Relative Humidity, Cloud coverage, Precipitation rate, and Mixing height are also saved out along each trajectory.

5. Airmass Transport to the West Coast Seattle, WA San Francisco, CA San Diego, CA Prob. of Airmass Traversing Asia = 0.08 Prob. of Airmass Traversing Asia = 0.045 The most probable long range transport to the West Coast occurs across the Pacific from the Russian coast eastward.

6. Airmass Transport to the Midwest Minneapolis, MN St. Louis, MO San Antonio, TX Prob. of Airmass Traversing Asia = 0.01 Prob. of Airmass Traversing Asia = 0.02 At Minneapolis, the springtime transport is from Canada. Transport to St. Louis is mostly from the North with some southerly contribution. San Antonio, receives the transport from the Gulf of Mexico with some contributions from the Great Plains and the West Coast.

7. Airmass Transport to the East Coast Boston, MA Norfolk, VA Miami, FL Prob. of Airmass Traversing Asia = 0.01 The springtime transport to Boston is from Eastern Canada. Transport to Norfolk is also mostly from the North with some contribution to from the South Atlantic sates. Miami receives its air from the Caribbean with some contribution from the the Eastern US.

8. Summary of Springtime Airmass Transport to the US The transboundary transport pattern to the US depends greatly on the receptor location (and season): The West Coast is impacted by airmasses from the West (Pacific and East Asia) The Central and Northern US receives air from Canada The Gulf States are under the influence of Atlantic and Caribbean air.

9. Future Analysis and Refinements The transport pattern depend on season. Need a full year transport climatology to the US Develop new methods for quantifying and displaying 3D transport e.g. separate examination of high and low elevation transport Where do the POPs come from? Global distribution of POPs sources How do POPs deposit from the atmosphere? Precipitation over the US. Are some regions of the US particularly sensitive? Alaska?

10. Monte Carlo Simulation of Trans-Pacific Dust Transport Monte Carlo simulation of the dust cloud transport. Blue 7 km Particle source locations in the Gobi Desert on April 19 th The dust cloud was (evidently) transported across the Pacific at about 4 km.

11. April 19 April 20 April 21 April 22 April 23 Transport Simulation TOMS Aerosol Index (Blue Particles 7 km)TOMS Aerosol Index

12. April 24 April 25 April 26 April 27 April 28 Transport Simulation TOMS Aerosol Index (Blue Particles 7 km)TOMS Aerosol Index