Impact of improved air quality during complete and partial lockdowns on surface energetics and atmospheric boundary...

Long-term measurements of meteorological, radiation, and aerosol profiles at a rural location have been used to study (i) the differences in spatial and vertical variation of aerosols during complete and partial lockdowns (LDs), (ii) the impact of these LDs on surface energetics and atmospheric boundary layer (ABL) height, and (iii) underlying processes that explain the variations in the above-measured parameters during LDs from the climatology. Large reduction in aerosol optical depth (AOD) and lidar (aerosol) backscatter up to the ABL height during complete and partial LD periods relative to climatology is observed, indicating improved air-quality during these periods. The reduction, in fact, is more during the partial LD imposed in 2021 (46 % in AOD) than during the complete LD (40 %) in 2020 over most part of peninsular India, partly due to higher rainfall during LD period of 2021. The reduction in aerosols during the LD periods increased the shortwave radiation by 59.8 W m^-2 and 76.9 W m^-2 in 2020 and 2021, respectively, relative to climatology. Contrary to the expected increase in temperature and ABL height due to higher insolation, both decreased during the LD. On the other hand, the absolute humidity increased during the above period. To shed more light on the above observations, rainfall and turbulent heat fluxes during the above periods were examined. More rain events and higher rain amount are observed during the LD periods of both years, which increased the soil moisture and modified the portioning of net radiation into turbulent fluxes. It increased the latent heat flux considerably and thereby the absolute humidity. On the other hand, the sensible heat flux has decreased, which in turn reduced the temperature and also the ABL height. The present study highlights the complex interplay of natural and anthropogenic processes in modifying land-atmospheric interaction and ABL dynamics.