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On March 16, 2020, Kolkata, a megacity located in the eastern part of India announced partial lockdown due to COVID-19 crisis ahead of the India-wide lockdown pronouncement with effect from March 25, 2020. This study presents an analysis for multiple pollutants with special focus on NO 2 and O 3, based on data from different monitoring stations located across Kolkata city, for the period of 16 March- 17 May 2020. A comparison was done with the pre-lockdown period of 1 st February – 15 th March 2020. Most significant reduction was observed in the concentration of nitrogen dioxide (NO 2 ) (- 76.8%), volatile organic compounds (VOCs) (- 69.5%), PM 10 (- 64.6%) and PM 2.5 (- 60.9%). A lower percentage reduction was found for CO, sulfur dioxide (SO 2 ) and ammonia (- 48.6%, - 41.7% and – 41.1% respectively). However, during partial lockdown, Lockdown Phase-1, Phase -2, and Phase -3 surface-level ozone (O 3 ) has changed respectively by 31.72%, 31.13%, -14.28% and -14.05% ; which resulted in an overall increase of 8.17% in the entire study period. The Air Quality Index (AQI) in Kolkata which was poor or very poor in the past even during lockdown period it failed to attain the ‘good’ standard. This needs special attention in human health impact assessment and public health management. We recommend that for policy attention and education/awareness-building efforts additional attention needs to be drawn towards stickiness in O 3 which have adverse human health and which went up during lockdown period compared to pre-lockdown period. We highlight some major policy implications of the observed trends to combat city air pollution along with climate co-benefits by shifting transport fuel and related infrastructure. These observations over several months provide a good database for any future air pollution control policy formulation and many more future research.
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Ghosh et al. (2020) studied this question.