It is well known that summer haze is responsible for producing bad air quality in the Midwest and Eastern US. However, the sources that contribute to the fate and transport of these aerosols are, to a large extend, unknown. On September 4, 2003 forest fires through the Northwestern US and British Columbia produced emissions that led to a large loading of aerosols in the troposphere. This initial loading of aerosol into the troposphere was captured by the MODIS derived-ta.

On September 8 - 11, a high-pressure system stagnated to the east of the Ohio River Valley creating meteorological conditions conducive to the formation of a large pollution event. The formation and the development of this pollution event was captured by the MODIS sensor aboard the Terra Satellite, which showed the significant enhancement of the MODIS derived-ta level (ta =~1.1 in Chicago, IL and Milwaukee, WI) over the Midwest and the persistence of the level for a couple of days until frontal clouds washed out the aerosols on September 15. Forward trajectory analysis and the time sequence of the MODIS derived-ta images strongly suggest that the formation of this large-scale pollution event was heavily influenced by the initial aerosol loading into the lower troposphere from the fires in the Northwest, the subsequent eastward transport and the subsidence associated with the high pressure system into the boundary layer.

On September 11, as well as subsequent days, elevated ground level 24 hour average PM2.5 concentrations in excess of 40.5 µg/m3 (Air Quality Index >100) were seen in many areas across the Midwest, including Chicago, IL and Duluth, MN.

During this large-sace pollution event we examined the relationship of MODIS-derived ta and surface PM2.5 concentrations over the mid-west. Results show a strong correlation coefficient between hourly PM2.5 concentrations (Surface Monitor) and ta in coincident MODIS pixels (10 km x 10 km). The results demonstrate that the MODIS derived ta holds great potential for tracking regional air pollution events.