Reflections Based on Pollution Changes Brought by COVID-19 Lockdown in Shanghai.

COVID-19 and its variants have been changing the world. The spread of variants brings severe effects to the global economy and to human's lives and health, as well as to society. Lockdown is proven to be effective in stopping the spread. It also provides a chance to study natural environmental changes with humanity's limited interference. This paper aims to evaluate the impact of lockdown on five major airborne pollutants, i.e., NO2, SO2, O3, PM2.5 and PM10, in the three different functional regions of Chongming, Xuhui and Jinshan of Shanghai. Changes in the same pollutants from the three regions over the same/different periods were all studied and compared. Overall, the COVID-19 lockdown has changed pollutant concentrations in the long and short terms. Concentrations of four pollutants decreased, except for that of earth surface O3, which increased. SO2 had significant correlations with all other pollutants. PM2.5 and PM10 are more externally input than locally produced. NO2, SO2 and PM levels sharply reduced in Jinshan and Xuhui due to the limited usage of fossil fuel. Lockdown improved the air quality. People now have a chance to rethink the value of life and the harmony between economic progress and environmental protection. This is helpful to establish sustainable societies.