Exploring the Potential of Satellite Data for Air Quality Applications

We explore the relationship between column aerosol optical thickness (AOT) derived from the Moderate Resolution Imaging SpectroRadiometer (MODIS) on the Terra/Aqua satellites and hourly fine particulate mass (PM_2.5) measured at the surface at seven locations in Jefferson county, Alabama for 2002. Results indicate that there is a good correlation between the satellite-derived AOT and PM_2.5 (linear correlation coefficient, R=0.7) indicating that most of the aerosols are in the well-mixed lower boundary layer during the satellite overpass times. There is excellent agreement between the monthly mean PM_2.5 and MODIS AOT (R>0.9), with maximum values during the summer months due to enhanced photolysis. The PM_2.5 has a distinct diurnal signature with maxima in the early morning (6:00~8:00AM) due to increased traffic flow and restricted mixing depths during these hours. Using simple empirical linear relationships derived between the MODIS AOT and 24hr mean PM_2.5 we show that the MODIS AOT can be used quantitatively to estimate air quality categories (e.g., good, moderate, unhealthy for special groups, unhealthy and hazardous) as defined by the U.S. Environmental Protection Agency (EPA) with an accuracy of more than 90% in cloud-free conditions. We emphasize that several factors including aerosol vertical distribution and local meteorological conditions could affect the correlation between satellite-derived AOT and PM_2.5 mass. Therefore, more research is needed before applying these methods and results over other areas. Similar analysis including plume transport model analysis over other PM_2.5 locations will also be presented.