Classification and transformation of aerosols over selected Indian cities during reduced emissions under Covid-19 lockdown

Studies in the recent past show improved air quality over India during the Covid-19 lockdown. This research attempts to characterize atmospheric aerosols in terms of alpha and AOD and their transformation over India during the pandemic lockdown. The type and particle distribution of aerosols, including gaseous species for five Indian regions were considered. Fine to coarse particle shift was observed in most regions. The northern region observed high fire counts, implying crop residue burning season during the stringent lockdown. Thiruvananthapuram, in the south, showed an increase in PM, owing to the resumption of mobility post-lockdown. Hyderabad, however; observed increased PM2.5 (2.79%) and AOD (37.23%) during Phase 1. Maritime (MT) aerosol predominated over Thiruvananthapuram, whereas urban/biomass burning (UBB) type decreased over the eastern region. Contributions from continental average (CA), maritime continental average (MCA), and MT were observed over Hyderabad, post-lockdown. In the central region, MCA was replaced by UBB and mixed type, with isolated episodes of clean continental (CC) and desert dust (DD). During lockdown phases, an increase in O-3 over western, northern, and central regions is attributed to increased temperature and decreased NO2. A significant correlation with population density (PD) exists with NO2 (R-2 = 0.75; p < 0.05), suggesting human mobility as a major contributor to NO2 in the atmosphere during the lockdown period.