Over the past several years, the remote sensing of trace gases and aerosols from space has improved dramatically. The emergence and application of these measurements adds a new dimension to air quality forecasting by enabling consistent observations of pollutants over large spatial domains. Current instruments aboard NASA and European Space Agency satellites can provide derived measurements of trace gases and aerosols relating directly to most of the EPA's criteria pollutants: ozone, NO2, SO2, CO, and particulate matter (PM10 and PM2.5).

For decades weather forecasters have used parameters derived from satellites to help forecast weather. Researchers are now showing that satellites can also help with forecasting air quality. In late summer 2003, NASA, NOAA, and US EPA prototyped a new forecast tool utilizing near-real-time aerosol optical depth , ta at 550 nm, derived from the MODIS sensor about the Terra Satellite (Kaufman et al., 1997; Tanre et al., 1997). The forecast tool involved the near-real-time data-fusion of MODIS derived ta, combined with hourly in-situ PM2.5 mass concentrations from EPA's continuous monitoring network, and NOAA/NCEP 48 hour forecast data, to provide a pseudo-synoptic view of aerosol and aerosol transport across the North American continent. This data product was provided to State and Local Air management Agencies and used internally within EPA to help improve the accuracy in EPA's next-day PM2.5 forecast. This paper provides an overview of this prototype project and a discussion of the impact of this forecast tool on next day PM2.5 forecasts in major metropolitan areas across the US.