Impact of COVID-19 lockdown on the fine particulate matter concentration levels: Results from Bengaluru megacity, India

Leveraging the COVID-19 India-wide lockdown situation, the present study attempts to quantify the reduction in the ambient fine particulate matter concentrations during the lockdown (compared with that of the pre-lockdown period), owing to the highly reduced specific anthropogenic activities and thereby pollutant emissions. The study was conducted over Bengaluru (India), using PM(2.5) (mass concentration of particulate matter having size less than or equal to 2.5 µm) and Black Carbon mass concentration (BC) data. Open-access datasets from pollution control board (PCB) were also utilised to understand the spatial variability and region-specific reduction in PM(2.5) across the city. The highest percentage reduction was observed in BC(ff) (black carbon attributable to fossil fuel combustion), followed by total BC and PM(2.5). No decrease in BC(bb) (black carbon attributable to wood/biomass burning) was observed, suggesting unaltered wood-based cooking activities and biomass-burning (local/regional) throughout the study period. Results support the general understanding of multi-source (natural and anthropogenic) nature of PM(2.5) in contrast to limited-source (combustion based) nature of BC. The diurnal amplitudes in BC and BC(ff) were reduced, while they remained almost the same for PM(2.5) and BC(bb). Analysis of PCB data reveal the highest reduction in PM(2.5) in an industrial cluster area. The current lockdown situation acted as a natural model to understand the role of a few major anthropogenic activities (viz., traffic, construction, industries related to non-essential goods, etc.) in enhancing the background fine particulate matter levels. Contemporary studies reporting reduction in surface fine particulate matter and satellite retrieved columnar Aerosol Optical Depth (AOD) during COVID-19 lockdown period are discussed.