Air pollution and critical air pollutant assessment during and after COVID-19 lockdowns: Evidence from pandemic hotspots in China, the Republic of Korea, Japan, and India

Abstract

The COVID-19 virus outbreak has been declared a “global pandemic”. Therefore, “lockdown” was issued in affected countries to control the spread of the virus. To assess air pollution during and after lockdowns, this study selected pandemic hotspots in China (Wuhan), Japan (Tokyo), Korea (Daegu), and India (Mumbai) and compared the Air Quality Index (AQI) in these areas for the past three years. The results indicated that air pollution levels were positively correlated with a reduction in pollutant levels during and after lockdowns in these cities. In Tokyo, low levels of air pollution, no significant change in the distribution of “good” and “moderate” days was observed during lockdown. In Daegu, mid-level air pollution, the percentage of “unhealthy” days (AQI>100) markedly reduced during lockdown; however, this reverted after lockdown was lifted. In Wuhan and Mumbai, high air pollution levels, the percentage of unhealthy days remarkably decreased during lockdown and continued to reduce after lockdown. It was found that PM 2.5 was the critical pollutant for all cities because its sub-AQI was the largest of the six pollutant species for the majority of days. In addition, PM 10 dominated the overall AQI for 2.2–9.6% of the period in Wuhan and Mumbai, and its sub-AQI reduced during lockdown. The mean sub-AQI for NO 2 , SO 2 , CO, and O 3 was within the “good” category for all cities. In conclusion, the lockdown policy reduced air pollution in general and this reduction was more significant for regions with high air pollution levels.

COVID-19 and Air Pollution: Measuring Pandemic Impact to Air Quality in Five European Countries

“…A decline of pollutants NO 2 , PM 2.5 , and PM 10 in many cases illustrate the clear benefit of forced lockdowns allowing the evaluation of the impact of pollutant concentration, and providing a better understanding of the impact industrial site activities have on air quality changes. All the study results shown above suggest that a direct improvement of air quality during the lockdown periods was visible in all countries [20,29,72]. A significant impact of COVID-19 lockdown on air quality improvement was found in all 4 countries and the Northern region of Italy, including a significant decrease in NO 2 concentration (see Figures 4-8).…”

Air quality characteristics in Wuhan (China) during the 2020 COVID-19 pandemic

“…We calculated the air quality index (AQI) ( Ministry of Environmental Protection of China, 2012 ) to evaluate the air quality characteristics in Wuhan from January to April/May during 2017–2020. AQI is an effective method for describing urban air quality and is widely used in many countries ( Tan et al, 2021 ; Heidarinejad et al, 2018 ; Hu et al, 2020 ).…”

Impact of COVID-19 containment and closure policies on tropospheric nitrogen dioxide: A global perspective

“…This allowed further studies to evaluate air quality later on in the pandemic as restrictions were eased, and compare these results to the air quality during the lockdown phase. These analyses agreed that the air quality improvements achieved during the lockdown period were only temporary as pollutant levels slowly increased again as lockdowns were lifted (Kumari et al, 2020; Liu et al, 2020a , Sulaymon et al, 2021 , Hu et al, 2021 ). Most previous studies compared trends before, during, and after policy implementation to investigate possible changes associated with mitigation measures, and focused on the short-term impacts of these policies.…”