# Changes of Air Pollution between Countries Because of Lockdowns to Face COVID-19 Pandemic
## 4 Concluding Remarks  
In general, the results of the study here, using updated data, are consistent with previous studies and lead to the main findings that containment strategies to prevent the rapid diffusion of COVID-19 pandemic (e.g., lockdown) also reduced air pollution, improving temporary air quality and the environment with a positive societal impact for the health of people. In particular, the statistical evidence above seems in general to support the _research hypothesis_ stated in the Introduction that the rate of change (reduction) of air pollutants can be explained by the restriction policies of lockdown applied by countries to face the rapid diffusion of the COVID-19 pandemic. Moreover, the findings here revealed that the effects of national restrictions on air quality vary significantly between countries. In fact, in March 2020, the countries that showed the maximum reduction in pollutant concentrations are France with CO (\(-4367.5\%\)), China and Australia for NO\({}_{2}\) (\(-150.5\%\)), Israel for SO\({}_{2}\) (\(-154.1\%\)), China for O\({}_{3}\) (\(-94.1\%\)), Germany for PM\({}_{2.5}\) (\(-41.4\%\)) and Turkey for PM\({}_{10}\) (\(-157.4\%\)). The variability of the observed improvements in air quality between regions may be due to the different geoeconomic, socioeconomic, environmental, climate, and atmospheric characteristics. These results suggest that the COVID-19 control measures imposed by governments of countries brought about a substantial decline in the concentration of air pollutants in contrast to pre-lockdown periods. It has been observed that the countries showed a greater decrease in air pollutant concentrations in March 2020, when they imposed mostly full lockdowns that led to constraints of the pollutant sources, such as transportation based on burning of gasoline and diesel, and industrial activities releasing a significant amount of greenhouse gases into the atmosphere. Manifold studies confirm that various strict measures of control taken by governments can mitigate/stop the spread of COVID-19 and also affect levels of air pollution in regions, comparing the primary and secondary air pollutant concentration values from air quality monitoring stations of COVID-19 pandemic period with the data of previous years. The majority of the results suggests that the concentrations of air pollutants substantially decreased during the period of lockdown, while the ozone concentration generally increased because of the decrease in nitrogen dioxide emissions, especially from motor vehicles and industrial activities. This study shows consistent results with previous literature and extends knowledge of the critical role of important and drastic interventions of public policy to face health emergencies, reduce air pollutants, and improve air quality and the environment in countries. However, it is also important to observe that measures of control to decrease the rapid spread of SARS-CoV-2 and cope with the COVID-19 pandemic crisis, such as lockdown, have pros and cons: they reduce, whenever possible, transmission dynamics and air pollution, but they have also negative consequences on economic systems, including integrated solid waste management (Figure 6). In short, strict restriction measures imposed by governments to combat the transmission of the COVID-19 pandemic (tracing systems, lockdown and quarantine, etc.) can improve air quality by mitigating greenhouse gas emissions and air pollutants based on anthropogenic sources, but they also can increase socioeconomic issues and mental health problems and the consequential diffusion in the environment of micropollutants in wastewater from the consumption of antidepressants, antibiotics and other drugs, as well as the increase of waste caused particularly by medicine usage, etc. [23; 103; 104; 105; 106; 107; 108; 109]. Even though this study has presented interesting findings, based on a new dataset, which are of course tentative, it has also limitations.