An Evaluation of Utilizing Passive and Active Satellite Aerosol Products as Proxies for Surface-Based PM2.5 Concentrations

Surface-based measurements of particulate matter concentrations, especially those of less than 2.5 µm in diameter (PM2.5), are critical metrics for monitoring and characterizing urban air quality. Recent studies have demonstrated the potential for using passive satellite aerosol optical depth (AOD) retrievals as proxies for PM2.5. However, uncertainties exist in passive satellite AOD datasets that need accounting for in corresponding PM2.5/AOD correlative studies. Further, surface-based PM2.5 concentrations do not necessarily show any direct relationship with column-integrated AOD.

Through the use of temporally and spatially-collocated PM2.5 datasets and AOD retrievals from Aqua/Terra Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging Spectroradiometer (MISR), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the impact of passive satellite AOD data quality on the PM2.5/AOD relationship, as well as the relationships between surface aerosol particle concentrations and total column extinction and AOD, are evaluated. This study shows that passive AOD retrieval data quality must be considered when drawing proxy estimates of surface-based PM2.5, as higher-quality AOD datasets exhibit increased correlation with PM2.5 across the contiguous United States (CONUS) versus standard off-the-shelf AOD products. However, these correlations still remain relatively low. 532 nm aerosol particle extinction coefficient retrievals from CALIOP derived closest to the surface (< 500 m) often do not correlate well with total column aerosol extinction. However, this relationship shows a regional distribution, with greater skill exhibited over the eastern CONUS compared with the west.