The outbreak of COVID-19 pandemic has impacted all the aspects of environment. The numbers of COVID-19 cases and deaths are increasing across the globe. In many countries lockdown has been imposed at local, regional as well as national level to combat with this global pandemic that caused the improvement of air quality. In India also lockdown was imposed on 25th March, 2020 and it was further extended in different phases. The lockdown due to outbreak of COVID-19 pandemic has showed substantial reduction of PM_2.5 concentrations across the cities of India. The present study aims to assess concentration of PM_2.5 across 12 cities located in different spatial segments Indo-Gangetic Plain (IGP). The result showed that there was substantial decrease of PM_2.5 concentrations across the cities located in IGP after implementation of lockdown. Before 30 days of lockdown, average PM_2.5 across cities was 65.77 µg/m³ that reached to 42.72 µg/m³ during lockdown periods (decreased by 35%). Maximum decrease of PM_2.5 concentrations has been documented in Lower Gangetic Plain (LGP) cities (57%) followed by Middle Gangetic Plain (MGP) cities (34%) and Upper Gangetic Plain (UGP) cities (27%) respectively. Among all the cities of IGP, maximum decrease of PM_2.5 concentrations was recorded in Kolkata (64%) (LGP) followed by Muzaffarpur (53%) (MGP), Asansol (51%) (LGP), Patna (43%) (MGP) and Varanasi (33%) (MGP).Therefore, this study has an immense potentiality to understand the impact of lockdown on a physical region (Ganga River Basin) and it may be also helpful for planners and policy makers to implement effective measures at regional level to control air pollution.

COVID-19 大流行的爆发已经影响了环境的各个方面。全球范围内的 COVID-19 病例和死亡人数正在增加。在许多国家，地方、区域和国家层面都实施了封锁，以应对导致空气质量改善的全球流行病。印度也于 2020 年 3 月 25 日实施了封锁，并在不同阶段进一步延长。由于 COVID-19 大流行爆发而导致的封锁表明，印度各城市的PM _{2.5浓度大幅降低。}本研究旨在评估位于印度-恒河平原 (IGP) 不同空间段的 12 个城市的 PM _2.5浓度。结果显示，PM _{2.5大幅下降}实施封锁后，IGP 内各城市的集中度。在封锁 30 天之前，城市的平均 PM _{2.5为 65.77 µg/m} ³ ，在封锁期间达到 42.72 µg/m ^{3 （下降了 35%）。}PM _2.5浓度下降幅度最大的是恒河下游 (LGP) 城市 (57%)，其次是恒河中平原 (MGP) 城市 (34%) 和恒河上游 (UGP) 城市 (27%)。在IGP所有城市中，PM _{2.5下降幅度最大}浓度记录在加尔各答 (64%) (LGP)，其次是 Muzaffarpur (53%) (MGP)、Asansol (51%) (LGP)、巴特那 (43%) (MGP) 和瓦拉纳西 (33%) (MGP)。因此，这项研究具有巨大的潜力来了解封锁对物理区域（恒河流域）的影响，也可能有助于规划者和政策制定者在区域层面实施有效的措施来控制空气污染。