1. Seasonal Airmass Transport Pathways to the US Prepared by: Rudolf B. Husar and Bret Schichtel CAPITACAPITA,Washington University, Saint Louis, Missouri 63130 Submitted to: Angela Bandemehr April, 2000, Draft

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 is small but under favorable emission and transport conditions it may cause elevated pollutant levels. Goal of Work: Illustrate the transboundary airmass transport to the United States The approach is to use backward airmass histories to 15 receptor points in the US, located mostly at the boundaries. The transport analysis was conducted over the entire calendar year 1999, aggregated monthly to illustrate the seasonal pattern of transport to each location This work is a spatial and temporal extension of the previous airmass history analysis for Spring 1998.previous airmass history analysis

3. Methodology: Airmass History Analysis For details see: Springtime Airmass Transport Pathways to the USSpringtime Airmass Transport Pathways to the US Backtrajectories are aggregated by counting the hours each ‘particle’ resided in a grid cell. The ‘residence time’, i.e. hours the Seattle, WA back trajectories resided over each grid cell Airmass history (Backtrajectory) Analysis Residence time Analysis

4. Location of Receptor Sites The 15 receptor sites were placed mainly at the US boundaries The calculations were performed for each receptor and month month for 1999. The calculations are described elsewhere.elsewhere All the calculations are completed. Next is an illustration of the seasonal transport results for four locations. Graphics for the complete set of receptors will be delivered shortly The quality of all the contour maps will also be improved.

5. Newport, OR (04) The air masses arriving to Oregon originate from the East throughout the year In July, the prevailing transport direction narrow, from the northeast During the other seasons, the transport direction is variable between NW and SW View monthly animation for Newport, ORNewport, OR

6. St. Louis, MO (12) The airmass transport direction to St. Louis, MO is seasonal In January-April, the prevailing transport is from N, NW In July-December, there is also a significant southerly component Interestingly, transport from the NE US to St. Louis is not significant View monthly animation for St. Louis, MOSt. Louis, MO

7. Big Bend, TX (10) Transport to Big Bend, TX varies seasonally In Jan-Apr, the transport is mainly from N, NW In July, the prevailing transport direction is narrow, from the E, SE In October, the transport is from variable directions View monthly animation for Big Bend, TXBig Bend, TX

8. Everglades, FL (13) Airmass transport to the Everglades, FL has several preferred pathways depending on season. In Jan-April, the transport is either from NW or from SW In July, the prevailing transport direction narrow, from the east In October, the transport wind directions are highly variable View monthly animation for the Everglades, FLEverglades, FL

9. Summary (tentative) At boundaries of the US the air is transported from different directions However, each receptor location has a climatologically well defined seasonal pattern Transport to the West Coast occurs primarily from the Pacific throughout the year Transport to the Southeastern US is form the north in the cold season and from the southeast during the warm season The above transport pattern are consistent with the know climatological regimes of N America (…..)