Impact of COVID-19 pandemic lockdown on air pollution in 20 major cities around the world

Abstract:

In order to fight against the spread of Covid-19, the most hard-hit countries implemented different lockdown strategies. To assess the impact of Covid-19 pandemic lockdowns on air quality in 20 major cities, we compared the Air Quality Index (AQI) of NO₂, SO₂, CO, ground-level O₃, PM_2.5 and PM₁₀ for the 2020 lockdown period with the past 3 years. The data were derived from the World Air Quality Index project (aqicn.org). Our findings reveal significant declines of AQI in NO₂, SO₂, CO, PM_2.5 and PM₁₀ in most cities, mainly due to the reduction of transportation, industry and commercial activities during lockdown. Furthermore, the severity of the lockdown corresponded with the reduction in NO₂. This work substantiates that the reduction of primary pollutants, especially NO₂, is mainly due to lockdown policy strictness. However, the decline of NO₂, SO₂ and PM_2.5 pollutant emissions also reflected environmental policy regulations, especially in Asian countries, where concentrations had been declining through the last 3 years. In contrast, the ground-level O₃ significantly increased in 4 cities, likely as a response of the decreased ratio of VOC/NOx. Meteorological variability also played key roles in changes of air pollutant AQI in some specific cities, as ground-level O₃ formation rate depends on temperature and rainfall can wash PM, NO₂ and SO₂ out of atmosphere.