Spatiotemporal variability of optical properties of aerosols over the Indo-Gangetic Plain during 2011–2015

The present study reports daily, monthly, and seasonal variations of aerosol optical depth (AOD) using aerosol robotic network (AERONET), MICROTOPS-II Sunphotometer, and Moderate Resolution Imaging Spectroradiometer (MODIS) data over three most polluted cities such as Kanpur, Varanasi, and Jaipur in the Indo-Gangetic Plain during 2011–2015. The monthly mean variations of AOD and Angstrom Exponent were also presented and compared with the meteorological parameters for all three cities. The concentrations of AODs in Kanpur and Varanasi were observed higher than in Jaipur throughout the study period. Overall maximum correlation (R2 = 0.74) was found in between AERONET and MODIS AOD in the winter season over Kanpur during 2011–2015, whereas the lowest correlation (R2 = 0.41) was found in between MICROTOPS-II Sunphotometer and MODIS AOD over Varanasi for the same period in the pre-monsoon season. Spectral variations of AODs at five different wavelengths, i.e., 380, 440, 500, 675, and 870 nm, were derived using AERONET for Jaipur and Kanpur and using MICROTOPS-II Sunphotometer for Varanasi during 2011–2015 inferred clearly that increasing wavelength provides decreasing AODs. The Hybrid Single-Particle Lagrangian Integrated Trajectories model was used for the backward trajectories analysis to assess the sources of large aerosol loadings over Jaipur, Kanpur, and Varanasi cities during some typical days.