LAUSR

Abstract This study investigates the impact of reduced anthropogenic emissions during the lockdown period on the concentration, composition, and characteristics of non-refractory particular matter ≤ 2.5 μm aerodynamic diameter (NR-PM2.5) and black carbon (BC) at Ahmedabad, a big city in western India. Online measurements were performed from February 29 to March 23 (before lockdown, P1), April 10 to May 01 (during the lockdown, P2), and June 1 to June 16 (post lockdown, P3) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and an Aethalometer. On average, organic aerosols (OA), NO3−, SO42−, NH4+, Cl−, BC at 370 nm (BC370), and BC at 880 nm (BC880) were reduced by 52, 64, 43, 62, 86, 52, and 57%, respectively, during P2 compare to P1. However, the diurnal trends of species were similar during the lockdown and no-lockdown periods. Source apportionment of OA using positive matrix factorization analysis revealed three factors: hydrocarbon–like organic aerosol (HOA), low volatile oxygenated OA (LV-OOA), and semi-volatile oxygenated OA (SV-OOA), contributing 26%, 44% and, 30%, respectively, to the total OA during the study period. Such studies are very crucial in assessing the effects of reduced anthropogenic emissions on the air quality of big cities, and planning appropriate mitigation strategies.