# Changes of Air Pollution between Countries Because of Lockdowns to Face COVID-19 Pandemic
## 3 Results and Discussion
### Asia Geoeconomic Region  
Variations in air pollutant concentrations in countries from the Asia geoeconomic region are visualized in Figure 1. When Figure 1 is examined for China, the air pollutant with the highest decrease in concentration values is NO\({}_{2}\) in January 2022 and January 2019, with a rate of 222% and 191%, followed by SO\({}_{2}\) in February 2021 and February 2020 with 171% and 161%, respectively (Figure 1, China). The times and rates of the maximum reduction in air pollutants other than NO\({}_{2}\) and SO\({}_{2}\) are CO with a rate of 137%, O\({}_{3}\) with a rate of 120%, PM\({}_{2.5}\) with a rate of 18% in March 2019, and PM\({}_{10}\) with a declining rate at 4% in February 2019. The full lockdown restrictions implemented in various cities in China, starting in January 2020, can be associated with these decreasing trends. [PERSON] et al. [80] investigated how the lockdown to face the COVID-19 pandemic (from 1 January to 12 April 2020) in China affected traffic-based air pollutants in Shanghai, comparing the pollutant concentrations during the pandemic period with the data from 2018 and 2019. They observed a moderate decline in CO emissions, with a ratio of 28.8% and 16.4% for roadside and non-roadside stations, respectively. In South Korea, the lockdown measures for pandemic control started on 25 March 2020 [81]. SO\({}_{2}\) showed the highest decreasing trend in January 2022 (\(-\)113%) and January 2021 (\(-\)103%), compared with the baseline period 2015-2018. The rate of decrease in the concentrations of air pollutants varied between 2.3% and 113%. While ozone levels increased compared to the baseline period in all periods except March 2020, PM\({}_{2.5}\) increased in January of 2019, 2020, 2021, and 2022, and in February and March of 2019 (see Figure 1, South Korea). [PERSON] et al. [81] explored the influences of the quarantine measure of control on the difference in air pollutant concentrations in Daegu, South Korea. They observed reductions in the concentrations of air pollutants: a ratio of 3.75% (PM\({}_{10}\)), 30.9% (PM\({}_{2.5}\)), 36.7% (NO\({}_{2}\)), 43.7% (CO), and 21.3% (SO\({}_{2}\)). In India, PM\({}_{2.5}\) concentration values decreased in February of 2019 (\(-\)4%) and 2020 (\(-\)3.6%), while the remaining periods showed an increasing trend in which the maximum level was observed in March 2021 (28%). By contrast, PM\({}_{10}\) decreased in March 2019 (\(-\)13%) and 2020 (\(-\)18%), while there was an increase of 0.2% in January 2022 and 31.3% in March 2021. All air pollutants, except PM\({}_{2.5}\) and PM\({}_{10}\), showed a decrease in the variation for almost all investigated periods; the most effective decrease was observed for CO, with a rate of 147% in January 2022 when pollutant concentrations are compared with the average values of the 2015-2018 baseline period (see Figure 1, India). Declines in the concentrations of CO (\(-\)84%), NO\({}_{2}\) (\(-\)69%), SO\({}_{2}\) (\(-\)5%), O\({}_{3}\) (\(-\)32%), and PM\({}_{10}\) (\(-\)18%) observed in March 2020 in India should be attributed to restrictions based on lockdown, which included the banning of all transport activities and the closure of industrial, commercial and private establishments, starting from March 2020. [PERSON] and [PERSON] [82] evaluated the impact of the total restriction of March 2020 on air quality parameters including PM\({}_{2.5}\), Air Quality Index (AQI), and tropospheric NO\({}_{2}\) in India using ground and satellite data. Results pointed out a declining trend in all air quality parameters studied (Figure 1, India). Figure 1: _Cont._  
In Israel, a remarkable decreasing trend was observed in CO (\(-180\%\)) and SO\({}_{2}\) (\(-154\%\)) in March 2020 which could be attributed to limitations imposed by Israel's government, including restrictions on the public and private sectors.