Compensatory effect of biomass burning on black carbon concentrations during COVID-19 lockdown at a high-altitude station in SW India.

The characteristics of black carbon (BC) aerosols, their sources, and their impact on atmospheric radiative forcing were extensively studied during the COVID-19 lockdown (28th March-31st May 2020) at a high-altitude rural site over the Western Ghats in southwest India. BC concentration and the contribution of BC originating from biomass burning (BC) estimated from the aethalometer model during the lockdown period were compared with the same periods in 2017 and 2018 and with the pre-lockdown period (1st February to March 20, 2020). BC concentrations were 44, 19, and 17% lower during the lockdown period compared with the pre-lockdown periods of 2020 and similar periods (28th March to 31st May) of 2017 and 2018, respectively. BC contributed ∼50% to total BC during the lockdown period of 2020 and compensated for the decrease in BC concentration due to lower traffic emissions. The characteristics of light-absorbing organic carbon (brown carbon; BrC) absorption at 370 nm were evaluated during the lockdown and the pre-lockdown periods of 2020, 2017, and 2018. The BrC was estimated to be the highest during the lockdown period of 2020. Finally, atmospheric radiative forcing was calculated using the mean BC concentration during the pre-lockdown, lockdown, and similar periods (28th March to 31st May) of 2017 and 2018.