An analysis and review on the global NO2 emission during lockdowns in COVID-19 period

During the COVID-19 pandemic, lockdowns at city-to-nation levels were enforced in many places in the world aiming to restrict the spread rate of COVID-19. Due to the forced restrictions, many human activities were considerably slowed down just within a few days, leading to drastic reductions in NO2 levels across the world. As reported, the nations and regions contributing to the huge NO2 emissions in the world such as China, United States, and Europe have seen a remarkable decline in NO(2 )during the lockdown period as compared to the same time of 2019, resulting in the estimation of reducing 20% of NO(2 )emissions in 2020 globally. This review paper has provided detailed information relating to the NO2 concentrations across most regions and countries in the world. Moreover, the effects of the behavior of countries during the lockdown as well as the main sources emitting NO2 emissions were also thoroughly analyzed. In general, this study is believed to supply useful information to the regulatory bodies for the strategies of the pollution source control. More importantly, controlling such temporary NO(2 )pollution source in a reasonable interval may be considered as a useful and effective measure to heal the environment and to reduce the pain of "the earth mother".