Benchrif Abdelfettah, Wheida Ali, Tahri Mounia, Shubbar Ramiz M, Biswas Biplab
National Centre for Nuclear Energy, Science and Technology (CNESTEN), Morocco.
Theoretical Physics Department, Physics Division, National Research Centre, Dokki, Cairo, Egypt.
Sustain Cities Soc. 2021 Nov;74:103170. doi: 10.1016/j.scs.2021.103170. Epub 2021 Jul 14.
Implemented quarantine due to the ongoing novel coronavirus (agent of COVID-19) has an immense impact on human mobility and economic activities as well as on air quality. Since then, and due to the drastic reduction in pollution levels in cities across the world, a large discussion has been magnetized regarding if the lockdown is an adequate alternative counter-measure for enhancing air quality. This paper aimed at studying the Air Quality Index (AQI), PM2.5, and tropospheric NO2 levels in three lockdown phases (before, during, and after) among 21 cities around the world. Simple before/after comparison approach was carried out to capture the declining trend in air pollution levels caused by the lockdown restrictions. The results showed that the frequency distribution for NO2 is more variable than that for PM2.5, and the distribution is flatter from 2020 to the baseline 2018-2019 period. Besides, AQI, in most of the cities, has varied from high to mild pollution during the lockdown and was moderate before. Although during the lockdown, a reduction of 3 to 58% of daily NO2 concentrations was observed across the cities, an increase was detected in three cities including Abidjan (1%), Conakry (3%), and Chengdu (10%). Despite this mixed trend, the NO2 time series clearly showed the effect of the unlocking phase where the NO2 levels increased in almost all cities. Similarly, PM2.5 concentrations have increased in the post-lockdown period, with 50% of the cities reporting significant positive differences between the lock and the unlock phase. Then, the levels of PM2.5 were higher at the pre-lockdown phase than at any other time exhibiting a "U" shape. In addition, during Ramadan, it was noted that altered patterns of daily activities in some Islamic cities have a significant negative impact on air quality.
由于新型冠状病毒（COVID-19病原体）的持续传播而实施的隔离措施，对人员流动、经济活动以及空气质量都产生了巨大影响。自那时起，由于全球各城市污染水平大幅下降，引发了一场关于封锁措施是否是改善空气质量的适当替代对策的大讨论。本文旨在研究全球21个城市在三个封锁阶段（之前、期间和之后）的空气质量指数（AQI）、细颗粒物（PM2.5）和对流层二氧化氮（NO2）水平。采用简单的前后比较方法来捕捉封锁限制导致的空气污染水平下降趋势。结果表明，NO2的频率分布比PM2.5的更具变化性，且从2020年到基线2018 - 2019年期间分布更平坦。此外，在大多数城市，AQI在封锁期间从高污染变为轻度污染，而之前为中度污染。虽然在封锁期间，各城市每日NO2浓度下降了3%至58%，但在包括阿比让（1%）、科纳克里（3%）和成都（10%）在内的三个城市中检测到浓度有所上升。尽管存在这种混合趋势，但NO2时间序列清楚地显示了解封阶段的影响，几乎所有城市的NO2水平都有所上升。同样，在封锁后时期PM2.5浓度有所增加，50%的城市报告在封锁和解封阶段之间存在显著的正向差异。然后，PM2.5水平在封锁前阶段高于其他任何时期，呈现出“U”形。此外，在斋月期间，注意到一些伊斯兰城市日常活动模式的改变对空气质量有重大负面影响。
