In order to control the widespread COVID-19, the government of India had imposed a nationwide lockdown on all non-essential activities from 22 March to 3 May 2020. Daily ambient PM10 , PM2.5 , NO, NO2 and O3 concentrations in Delhi and Kolkata from 1 March to 3 May period of 2019 and 2020 were collected from different monitoring stations along with meteorological data to study the impact of COVID-19 lockdown on ambient pollutant concentrations. Average ambient concentrations of PM10 and PM2.5 were significantly decreased (Delhi: 59% and 43% respectively and Kolkata: 49% and 50% respectively) during the lockdown period compared to the same period during 2019 in both cities. Average ambient O3 concentration in Delhi was significantly lower in 2020 (38.5 μg m-3 ) compared to 2019 (44.7 μg m-3 ) during the study period. However, average ambient O3 concentration was significantly higher during 2020 (46.9 μg m-3 ) compared to 2019 (31.4 μg m-3 ) in Kolkata. Effect size analysis of different predictive variables concludes that the lockdown period explains maximum variation in ambient concentrations of PM10 andPM2.5 during 2020 in both cities. However, maximum variation in ambient O3 concentrations in both cities was explained primarily by spatial variation rather than the lockdown period. The study suggests, major policy implementation related to the transport and industrial sectors that aims to address the ambient air pollution problem in India may reduce the ambient particulate matter concentrations, though it may not have a significant effect on other ambient air pollutants such as O3 in major Indian cities. This article is protected by copyright. All rights reserved.

中文翻译：

---

德里和加尔各答的 COVID-19 封锁是否改善了这两个城市的环境空气质量？

为了控制广泛的 COVID-19，印度政府在 2020 年 3 月 22 日至 5 月 3 日期间在全国范围内对所有非必要活动实施了封锁。德里和德里的每日环境 PM10、PM2.5、NO、NO2 和 O3 浓度从不同监测站收集了 2019 年和 2020 年 3 月 1 日至 5 月 3 日期间的加尔各答以及气象数据，以研究 COVID-19 封锁对环境污染物浓度的影响。与 2019 年同期相比，封锁期间 PM10 和 PM2.5 的平均环境浓度显着降低（德里：分别为 59% 和 43%，加尔各答：分别为 49% 和 50%）。在研究期间，德里的平均环境 O3 浓度在 2020 年（38.5 μg m-3 ）显着低于 2019 年（44.7 μg m-3 ）。然而，与 2019 年（31.4 μg m-3 ）相比，2020 年的平均环境 O3 浓度（46.9 μg m-3 ）明显更高。不同预测变量的效应大小分析得出的结论是，封锁期解释了 2020 年两个城市 PM10 和 PM2.5 环境浓度的最大变化。然而，这两个城市的环境 O3 浓度的最大变化主要是由空间变化而不是封锁期来解释的。该研究表明，旨在解决印度环境空气污染问题的与交通和工业部门相关的重大政策实施可能会降低环境颗粒物浓度，尽管它可能不会对其他环境空气污染物（如 O3）产生显着影响。印度主要城市。本文受版权保护。版权所有。