# Changes of Air Pollution between Countries Because of Lockdowns to Face COVID-19 Pandemic
###### Abstract  
The goal of this study is to analyze how levels of air pollution changed between countries with their restriction policy of lockdown to cope with the COVID-19 pandemic. The study design compares average changes of CO, NO\({}_{2}\), SO\({}_{2}\), O\({}_{3}\), PM\({}_{2.5}\) and PM\({}_{10}\) concentrations based on measurements at ground level in January, February, and March for the years 2019, 2020, 2021, and 2022 (during the COVID-19 pandemic crisis) to average values of a 2015-2018 baseline period (ex-ante COVID-19 pandemic) between 300 cities in 19 countries of five geoeconomic regions. Results reveal that the maximum reduction in air pollutant concentrations is given by: CO (\(-\)4367.5%) in France, NO\({}_{2}\) (\(-\)150.5%) in China and Australia, SO\({}_{2}\) (\(-\)154.1%) in Israel, O\({}_{3}\) (\(-\)94.1%) in China, PM\({}_{2.5}\) (\(-\)41.4%) in Germany, and PM\({}_{10}\) (\(-\)157.4%) in Turkey. Findings show that the effects of restriction policies for COVID-19 pandemic on air quality vary significantly between countries, depending on the different geographical, economic, industrial and social characteristics of the countries. These results clarify the critical relationship between control measures for pandemic crises and levels of air pollution in countries that can support best practices of environmental policy for pathways of sustainable development. COVID-19 pandemic; restriction policies; lockdown; air pollution; atmospheric pollution; air pollutants; air quality monitoring; air quality; environmental policy; climate change Article Changes of Air Pollution between Countries Because of Lockdowns to Face COVID-19 Pandemic. _Applied_  
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Manifold studies show the effects of lockdown measures on levels of air pollutants and air quality in countries. [PERSON] et al. [30] determined the effects of the quarantine on air quality in the Yangtze River Delta region of Eastern China. Results suggest remarkable declines in the concentrations of air pollutants from industry and traffic emissions because of the diminishing of socioeconomic activities. The reduction in pollutant concentrations in 2020, which contributed considerably to the improvement of the region's air quality, was found for fine particulate matter (PM\({}_{2.5}\)), nitrogen dioxide (NO\({}_{2}\)), and sulfur dioxide (SO\({}_{2}\)), when data were compared to the year of 2019 [30]  
[PERSON] et al. [31] analyze the impact of the quarantine measures on the air pollution in the city of Naples, Italy, from 13 March to 4 May 2020, analyzing gaseous pollutants (benzene, C\({}_{6}\)H\({}_{6}\)), carbon monoxide (CO), NO\({}_{2}\) and SO\({}_{2}\) and particulate matter (PM\({}_{10}\), PM\({}_{2.5}\), PM\({}_{1}\)) at ground level. Results showed that NO\({}_{2}\) was reduced by 49-62% in urban and green suburban areas, although CO and SO\({}_{2}\) indicated a higher decrease in urban or industrial regions of the city (50-58% and 70%, respectively). PM concentrations also showed a reduction ranging between 29 and 49% [31]. Another study by [PERSON] et al. [32] investigated the way that levels of air pollutants (PM\({}_{2.5}\) and tropospheric NO\({}_{2}\)) changed before, during, and after a lockdown in 21 cities in different countries. Results exhibited a drop in NO\({}_{2}\) concentrations ranging from 3 to 58% during the lockdown period, except for three cities (Abidjan, Conakry, and Chengdu), which observed an increase in the NO\({}_{2}\) levels at a rate of 1, 3 and 10%, respectively. Instead, PM\({}_{2.5}\) levels exhibited an increase after the lockdown period. [PERSON] et al. [33] analyzed the differences in air pollutants (CO, NO\({}_{2}\), SO\({}_{2}\), O\({}_{3}\), PM\({}_{2.5}\), and PM\({}_{10}\)) by comparing the quarantine period of March and April 2020 to the same months in 2015 and 2019. Globally, NO\({}_{2}\) levels decreased by around 9.19% and 9.57% in March and April 2020.