Air quality during three covid-19 lockdown phases: AQI, PM2.5 and NO2 assessment in cities with more than 1 million inhabitants

Abstract

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.

Empirical evidence shows that air quality changes during COVID-19 pandemic lockdown in Jakarta, Indonesia are due to seasonal variation, not restricted movements

“…Such a trend was also reported Rodríguez-Urrego and Rodríguez-Urrego (2020) , who concluded that air quality in Jakarta worsened due to the lockdown. Benchrif et al (2021) noted that a remarkable increase in PM2.5 concentration despite the lockdown measure. They attributed the increase due to the mobility of vehicles that remained in operation during the pandemic and to using private vehicles instead of public transportation.…”

The daily urban dynamic indicator: Gauging the urban dynamic in Porto during the COVID-19 pandemic

“…Thus, these activities’ behaviour can be extrapolated from the analysis of changes in the emissions of pollutants. On this behalf, Benchrif et al (2021) summarized the most recent studies addressing the evolution of air pollutants during the pandemic, concluding that the lockdown lead to a drastic reduction of air pollution levels at the cost of the normal functioning of urban activity, including road traffic and industry. Likewise, Wang & Li (2021) looked at the non-linear relationship between the impact of the COVID-19 lockdown and four pollutants in eight cities worldwide (Wuhan, New York, Milan, Madrid, Bandra, London, Tokyo and Mexico City), showing that the global lockdown reduced concentrations of NO 2 in these cities, up to 50% during 2020.…”

Particle composition, sources and evolution during the COVID-19 lockdown period in Chengdu, southwest China: Insights from single particle aerosol mass spectrometer data

“…Although many studies have reported the effects of COVID-19 lockdown on the air pollution in many cities in China, studies on Sichuan province or southwest China are fewer. At the same time, those studies on Sichuan province that have been conducted mainly focused on the variations in air pollution indexes (PM 2.5 , PM 10 , SO 2 , NO 2 , CO and O 3 ) before and during the lockdown period ( Benchrif et al, 2021 ; Deng et al, 2021 ; Fan et al, 2021 ; Wang et al, 2020c ; Zhang et al, 2020 ), and there is almost no in-depth research on the chemical composition, source and pollution formation mechanism of particulate matter. Therefore, in order to obtain more information about the effects of the COVID-19 lockdown on air pollution in southwest China, single particle aerosol mass spectrometer (SPAMS) observations, as well as those from other types of online observation equipments, were used to measure the atmospheric single aerosol particles and gaseous pollutants in Chengdu, the capital city of Sichuan province, before and during the lockdown period.…”