Satellite remote sensing of particulate matter in the atmosphere of megacities: A case study of Tehran, Iran

Here, we investigate the annual variations of particulate matter (PM) levels for Tehran megacity during 2018, using ground-based measurements and remotely sensed data, taken from CALIOP space-borne lidar and MODIS-Aqua sensor. Furthermore, the aerosol types of Tehran are determined against three other megacities, namely Delhi, Helsinki and Calgary. Satellite data attest the dust/polluted dust as the dominant aerosol types in Tehran during warm/cold seasons, respectively. The values of particulate depolarization ratio (PDR), particulate color ratio (PCR) and aerosol optical depth (AOD) are calculated along the CALIPSO satellite night-time trajectories over Tehran. This demonstrates that the maximums of PDR and PCR occur during July. The seasonal analyses of vertically averaged PDR and PCR attest that the maximum values take place during summer time, while minimum records belong to the fall season. The correlation analysis emphasizes a sensible conformity between column AOD data (retrieved from MODIS-Aqua sensor) and the PM2.5 concentrations (acquired from ground -based meteorological stations). Besides, PDR is inversely correlated to relative humidity. In this study, the origins of pollutants are envisaged based on PSCF and frequency analysis of back-trajectories for February and July 2018, indicating the main origin of dust arises from Turkmenistan deserts in summer and Iraq/western Iran arid areas during winter.