The present study is an attempt to understand the level of PM2.5 pollution and its toxicity based on the oxidative potential (OP) during the winter-time pollution period over Kolkata, a megacity at the eastern most parts of Indo-Gangetic Plain (IGP) during the period of 2016-2023. We have assessed the effectiveness of the Government of India's national mission, the National Clean Air Program (NCAP) in PM2.5 reduction over this city, and the study revealed that the mission has been efficacious in lessening the PM2.5 load by 28 % from pre-NCAP (2016-2019) to post-NCAP (2021-2023) periods. Several policy interventions reduced the contributions from various anthropogenic sources; however, biomass/solid waste burning remained a major concern with no significant reduction. The results revealed that the volume-weighted OP (OPv) remains mass-independent and the same when PM2.5 remains within 70 μg m-3 (OPv range between 2.7 and 3.1 nmol DTT min-1 m-3). With the rise in PM2.5 mass from 70 μg m-3, OPv boosts up sharply and reaches its peak (at ∼145 μg m-3 during pre-NCAP and ∼105 μg m-3 during post-NCAP) followed by an insignificant change with the further rise in PM2.5. We observed that biomass/solid waste burning is the major concern over Kolkata in the current scenario (post-NCAP) even after NCAP policy interventions. Such high OP-based toxicity of PM2.5 during post-NCAP periods could be minimized if actions are taken against this particular source.
Keywords: Biomass burning; IGP apportionment; Oxidative potential; Toxicity standard; Urban metropolis.
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