Spectral, spatial, and temporal sensitivity of correlating MODIS aerosol optical depth with ground-based fine particulate matter (PM2.5) across southern Ontario

This paper evaluates the sensitivity of the aerosol optical depth (AOD) measurements derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) at wavelengths of 0.47, 0.55, and 0.66 mm from both the Terra and Aqua satellites for the estimation of ground-level concentrations of fine particulate matter (PM2.5) in southern Ontario, Canada. The correlation between MODIS AOD and ground-based PM2.5 measurements is compared at different seasons and spatial aggregation levels. The results showed that the MODIS AOD data acquired in early afternoon (from Aqua) seem to have slightly higher agreement with the ground-based measurement of PM2.5 than the late morning Terra data. Moreover, MODIS AOD at 0.47 mu m from both satellites had the highest correlation with ground-level PM2.5. More detailed examination suggested that the correlation was stronger in the spring and summer and weaker in the fall and winter. Aqua MODIS AOD appeared to have a better correlation with the average ground-based PM2.5 concentration over 1-3 h than with daily PM2.5. MODIS AOD values aggregated over 3 x 3 pixel groups correlate slightly better with PM2.5 than with the original single centre pixel values.