# Changes of Air Pollution between Countries Because of Lockdowns to Face COVID-19 Pandemic
## 3 Results and Discussion
### Europe  
Figure 4 shows results for Europe. In Germany, a nationwide lockdown was imposed between 21 March and 30 June 2020 ([PERSON] et al., 2021). The maximum decreases in NO\({}_{2}\) (\(-\)30%) and SO\({}_{2}\) (\(-\)191%) concentrations were observed in January 2022, whereas the maximum decrease in PM\({}_{2.5}\) concentration was in February 2022 (Figure 4, Germany). In general, there is a decrease in the concentration of all parameters of air pollution associated with restrictions. [PERSON] et al. [18] found that human-based emissions in eight German metropolitan regions reduced by 23% for NO\({}_{2}\), while they increased by 4% for O\({}_{3}\) between the examined periods. In the Netherlands (Figure 4, The Netherlands), the restriction period based on lockdown was from 16 March 2020 to 10 May 2020 [89].The average values of the 2015-2018 baseline period were compared with values during the lockdown period; results showed a significant decrease in CO concentration in the Netherlands: NO\({}_{2}\) (\(-\)26%), SO\({}_{2}\) (\(-\)35%), PM\({}_{2.5}\) (\(-\)17%), and PM\({}_{10}\) (\(-\)18%) in March 2020 had lower levels than March in the 2015-2018 period, already before the lockdown period (see Figure 4, The Netherlands). [PERSON] et al. [89] also investigated the Netherlands and showed that the lockdown reduced observed NO\({}_{2}\) concentrations with larger values than results obtained from simulation models. In Spain, the lockdown was applied from March 2020 to June 2020 [34]. CO showed the maximum decrease in its concentration during the examined months in 2022. Comparative analysis with the baseline period also showed reductions in NO\({}_{2}\) (\(-\)57%), SO\({}_{2}\) (\(-\)46%), and PM\({}_{10}\) (\(-\)15%) (see Figure 4, Spain). [PERSON] et al. [34] compared the air pollution level in Valencia, Spain between lockdown and non-lockdown periods. The highest reductions in the PM\({}_{10}\) and PM\({}_{2.5}\) levels were in the range of 56-60% and 41-53%. Figure 4: _Cont_. Figure 4: _Cont._  
In France, the lockdown restrictions were from 17 March 2020 to 11 May 2020 [90]. An extremely remarkable decrease in CO concentrations, up to over 4500%, was observed for almost all periods under study. In general, all pollutants decreased compared to the baseline period: NO\({}_{2}\) (\(-\)53%), SO\({}_{2}\) (\(-\)62%), PM\({}_{2.5}\) (\(-\)24%), and PM\({}_{10}\) (\(-\)10%) concentrations (see Figure 4, France). [PERSON] et al. [90] also indicated that the maximum daily concentrations of the air quality parameters showed decreasing levels in the range of 5.1 and 44.48%. In the United Kingdom, the lockdown was announced starting on 24 March 2020 because of the rapid increase in confirmed cases [71]. Pollutants mostly decreased compared to the baseline period: March 2022 for CO (\(-\)71%), February 2022 for NO\({}_{2}\) (\(-\)57%), February 2021 for SO\({}_{2}\) (\(-\)79.5), January 2021 for O\({}_{3}\) (\(-\)11%), February 2022 for PM\({}_{2.5}\) (\(-\)38%) and February 2022 for PM\({}_{10}\) (\(-\)49%). In addition, in March 2020, when the restriction policies started, all concentrations of air pollutants except ozone showed decreasing trends (see Figure 4, The United Kingdom). [PERSON] et al. [71], investigated the changes in air pollutant concentrations in the United Kingdom by comparing daily pollutant measurements of NO\({}_{2}\), O\({}_{3}\), and PM\({}_{2.5}\) during the lockdown period (from 30 March 2020 to 3 May 2020) with the 2017-2019 period. Results revealed that NO\({}_{2}\) and PM\({}_{2.5}\) concentrations reduced, while O\({}_{3}\) concentrations increased. Figure 4: Average concentrations of air pollutant in countries of the European geoeconomic region. Note: In Germany, the concentration of CO varied in the range of 0.10–0.26 ug/m\({}^{3}\) for the examined periods. Since CO concentration was low compared with the concentrations of other pollutants, it is not included in the graphs. In Croatia, the lockdown restrictions started on 16 March 2020 [91].