Trans-Pacific Transport Modeling of Particulate Matter and Ozone

There is increasing evidence that air pollutants originating from regions outside of North America such as Asia could impact U.S. domestic air quality. At the same time, the U.S. is both an importer and exporter of air pollutants. A pioneer modeling project, the “Intercontinental Transport and Climatic Effects of Air Pollutants” (ICAP) project, has been undertaken at U.S EPA to help understand and assess these impacts associated with the intercontinental transport of air pollutants, including particulate matter (PM), ozone (O3), and mercury (Hg). The on-going modeling efforts include a series of modeling (108-km grid resolution) and emissions related activities over the pacific regions, including a 2001 Base year simulation, 2030 scenarios (IPCC's A1B and B2 scenarios), and several sensitivity studies (e.g., removal of man-made Asian emissions and North America emissions, etc.). The trans-Atlantic modeling effort has also been under way. The key modeling tool used in this project is the Models-3/Community Multi-scale Air Quality (CAMQ) modeling systme developed at EPA.

The trans-Pacific modeling results revealed that PM2.5 and ozone can be transported across the Pacific Ocean over a time period of 5 to 10 days before reaching North America and U.S. A sensitivity study by removing the Asia man-made showed that the impact of Asia man-made emissions on America appeared to be persistent through the entire year, although exhibiting seasonal variations. The spring (April) had higher impact for PM 2.5 up to 2 ug/m3 (monthly average) in the western U.S. and up to 1 ug/m3 in the eastern U.S., while the summer (July) and spring (April) has comparable impacts for O3, up to 5~6 ppb (daily max) in the western U.S. and up to 2 ppb in the eastern U.S. The results of future scenarios modeling indicated tht sustainable development (IPCC B1 case) will have significant improvement over the continued growth (IPCC A1B case) on the air quality across the Pacific regions.