Variability in air-pollutants, aerosols, and associated meteorology over peninsular India and neighboring ocean regions during COVID-19 lockdown to unlock phases

Abstract

The study focuses on the variability in aerosols, air-pollutants, and associated meteorological characteristics over peninsular India and neighboring ocean regions during both lockdown (25 March-31 May) and unlock (June–September) periods in 2020. During first lockdown phase, 40–60% reduction in aerosol loading observed over most parts except central-west India and the southern BOB. HYSPLIT model-based ‘back trajectory’ suggests the increase in anthropogenic aerosols over BOB due to long-range transport from an elevated layer. During second lockdown phase, an increase in AOD found over the eastern parts of India might come from the continuous operation of coal-fired thermal power plants and coal mines, besides domestic emissions. A surge in sea salt aerosols over BOB during the last two lockdown phases could be due to the Amphan super cyclone. During unlock phases, only natural aerosols show significant variation over the coastal and neighboring ocean regions with the simultaneous presence of intense summer monsoon. However, anthropogenic aerosols increased over the inland areas, which is most prominent in second and fourth unlock phases and could be attributed to the long-range transport. Temporal analysis of particulate matters and gaseous pollutants over coastal cities suggests Ahmedabad to be the most polluted one. The highest fall in NO2 was observed over Mumbai, whereas O3 concentration was appreciably enhanced over Ahmedabad, Visakhapatnam, and Chennai. Besides low anthropogenic emissions, long-range transport and prevailing meteorological conditions also played a significant role in governing the observed changes in aerosol loading and air pollutant concentration.