Recent studies concluded that air quality has improved due to the enforcement of lockdown in the wake of COVID-19. However, they mostly concentrated on the changes during the lockdown period, and the studies considering the consequences of de-escalation of lockdown are inadequate. Therefore, we investigated the changes in fine particulate matter (PM_2.5) during the pre-lockdown, strict lockdown, unlocking, and post-lockdown scenarios. In addition, we assessed the influence of meteorology, mobility, air mass transport, and biomass burning on PM_2.5 using Google’s mobility data, back trajectory model, and satellite-based fire incident data. Average PM_2.5 concentrations in Ghaziabad, Noida, and Faridabad decreased by 60.70%, 63.27%, and 60.40%, respectively, during the lockdown. When compared with the preceding year (2019), the reductions during the shutdown period (25 March–31 May) were within the range of 36.34–44.55%. However, considering the entire year, this reduction in PM_2.5 is momentary, and a steady increase in traffic density and industrial operations within cities during post-lockdown reflects a potent recovery of aerosol level, during which the average mass of PM_2.5 three- to four-folds higher than the lockdown period. Back trajectories and fire activity results showed that biomass burning in the nearby states (Haryana and Punjab) influence aerosol load. We conclude that a partial lockdown in the event of a sudden surge in pollution would be a beneficial approach. However, reducing fossil fuel consumption and switching to more environmentally friendly energy sources, developing green transport networks, and circumventing biomass burning are efficient ways to improve air quality in the long term.

最近的研究得出结论，由于 COVID-19 后实施的封锁，空气质量有所改善。然而，他们大多集中在封锁期间的变化，而考虑解除封锁的后果的研究还不够。因此，我们研究了封城前、封城、封城、封城后细颗粒物（PM _2.5 ）的变化情况。此外，我们还利用 Google 的移动性数据、后向轨迹模型和基于卫星的火灾事件数据评估了气象、移动性、空气质量运输和生物质燃烧对 PM _2.5的影响。封锁期间，加济阿巴德、诺伊达和法里达巴德的 PM _2.5平均浓度分别下降了 60.70%、63.27% 和 60.40%。与上一年（2019年）相比，停工期间（3月25日至5月31日）减少了36.34%至44.55%。然而，从全年来看，PM _2.5的下降是暂时的，封城后城市内交通密度和工业运营的稳步增加反映了气溶胶水平的有力恢复，在此期间 PM _2.5的平均质量为三至比封锁期间高出四倍。回溯轨迹和火灾活动结果表明，附近各邦（哈里亚纳邦和旁遮普邦）的生物质燃烧会影响气溶胶负荷。我们的结论是，如果污染突然激增，部分封锁将是一种有益的方法。 然而，减少化石燃料消耗、转向更环保的能源、发展绿色交通网络以及避免生物质燃烧是长期改善空气质量的有效方法。