A view of Aerosol Optical and Microphysical Properties over the Indian Subcontinent from two Decades (2000-2020) of Multi-Angle Imaging SpectroRadiometer (MISR) Observations

Abstract:

Aerosols play a major role in influencing the Earth’s climate system. To improve their representation in the climate models, we need to have a robust understanding of the long-term changes in aerosol radiative properties. Multi-Angle Imaging SpectroRadiometer (MISR) onboard EOS-Terra spacecraft has been measuring aerosol optical and microphysical properties for the last 20+ years. Here we utilize 20 years (2000–2020) of MISR observations to examine the seasonal climatology and trends of aerosol characteristics over the Indian subcontinent.

We processed Level 2, version 23 MISR aerosol product retrieved at 4.4 km resolution and re-gridded them into 0.25°×0.25° resolution to match with the resolution at which the national emission inventory is available and most of the regional climate models are run. MISR aerosol product includes size‐ and shape‐segregated aerosol optical depth (AOD) and Ångström exponent (AE) and single scattering albedo (SSA). The MISR aerosol product is evaluated against AERONET sites in India to examine whether the retrieval quality has improved from version 22 to 23. The spatial patterns in the aerosol properties are analyzed in view of the emissions of primary particulates and secondary precursors, topography and meteorology.

High AOD over the eastern Indo-Gangetic Plain (IGP) observed during the winter season (Dec-Feb) in the previous studies is found to persist in 20-year climatology, suggesting no significant change in the spatial emission pattern and meteorology in the last twenty years. Using a combination of size- and shape-segregated AOD, we further map the seasonal changes in aerosol types. We observe a decline in dust activity over the western arid regions in the last twenty years during the pre-monsoon (Mar-May) season, while the anthropogenic aerosol loading has significantly increased in the eastern western and Peninsular India during the winter and over almost the entire country (except the arid region) during the post-monsoon (Oct-Nov) season. Our results are highly useful for the modelers to test the efficacy of the climate models in representing aerosol properties over this region.