Asheshwor Man Shrestha, Uttam Babu Shrestha, Roshan Sharma, Suraj Bhattarai, Hanh Ngoc Thi Tran, Maheswar Rupakheti

Drastic measures such as lockdown taken by countries worldwide to contain spread of COVID-19 have influenced air pollution dynamics substantially, at a planetary scale. Several media reported the lockdown induced air pollution reduction based on quickly assembled satellite observations. However, a global-scale analysis of such reduction in air pollution backed by quality data collected from ground stations across the world and the effects of lockdown to it are missing. Here, we investigate changes in concentrations of six air pollutants: PM2.5, PM10, O3, SO2, CO, and NO2 in 40 cities between February, March 2019 and 2020. The mean monthly concentrations of PM2.5 and PM10 in February and March of 2020 were found consistently lower than in 2019 in most of the cities. After lockdown, declines of anthropogenic pollutants such as NO2, CO, PM2.5 and PM10 concentrations were seen in 19, 9, 8 and 7 cities respectively. Improvement in air quality following lockdown was observed in the worlds most polluted cities including Bangalore, Beijing, Bangkok, Delhi, and Nanjing, as well as the worlds major trade centers including New York, London, Paris, Seoul, Sydney, and Tokyo. More visible reduction of air pollution remains to be seen if the lockdown is prolonged. Nevertheless, such reductions are expected to be temporary because the levels are likely to go up again once the situation gets back to normal.