Source apportionment of black carbon and the impact of COVID-19 lockdown over a semi-urban location in India

To reduce emissions and thereby decrease the effect of black carbon (BC) on human health and the climate, the knowledge of BC concentrations and quantification of its contributions from different sources are necessary for establishing strategies for policymakers. The lockdown due to the COVID-19 pandemic has provided a unique scenario to analyze the impact of anthropogenic activities on BC concentration and their sources. In this study, the variation in BC mass concentration (eBC), its source apportionment, absorption angstrom exponent and their inter-annual variations, and the impact of COVID-19 lockdown on BC are analyzed using a six-year observation of eBC (from the year 2016-2021) over a semi-urban location (Vijayawada (16.44 degrees N, 80.62 degrees E), 30m a.m.s.l) in India. BC mass concentration peaks during the morning (around 06:00-08:00 LT) and evening (after 18:00 LT) hours and is low during the daytime. High eBC is observed during the winter season whereas low eBC during the monsoon season. The source apportionment of BC is carried out using the aethalometer model and it shows that the major source of BC over the site is fossil fuel combustion (>60%) along with a non-negligible contribution from biomass burning (<40%). This result is supported by the absorption angstrom exponent values of less than 1.6 during all seasons. A significant decrease (30%) in the total eBC over the site is observed during the COVID-19 lockdown days. It clearly shows the impact of the reduction in the contribution from anthropogenic activities mainly vehicular and industrial emissions (fossil fuel combustion) on the BC concentration. Interestingly, even after significant reduction of fossil fuel source emission during the lockdown, 53% of BC over the observational site is still contributed by fossil fuel combustion. This obviously shows the dominance of long-range transported BC due to fossil fuel combustion over the observational site.