Air Quality Transformation in Twelve Major Cities during Covid-19 Lockdowns: A Global Assessment

Abstract

The implementation of lockdown measures worldwide, aimed at preventing the spread of Covid-19, has temporarily improved air quality. This research paper aims to examine the impact of the lockdown period from March to May 2020 on the levels of four common air pollutants in 12 major cities, namely Delhi (India), Newcastle (UK), California (USA), Brescia (Italy), São Paulo (Brazil), Langfang (China), Madrid (Spain), Khon Kaen (Thailand), Santiago (Chile), Bogota (Colombia), Wellington (New Zealand), and Silivri (Turkey). The study analyzed the changes in average monthly concentrations of nitrogen dioxide (NO₂), ozone (O₃), and particulate matter (PM10 and PM_2.5) during two phases: the pre-lockdown and lockdown phases. During the lockdown, all air pollutants except ozone exhibited a significant decrease. These results highlight the positive impact of reducing anthropogenic emissions on air quality during the Covid-19 lockdown. The researchers also used principal components analysis to examine the concentrations of NO₂, O₃, PM_2.5, and PM10 from January 2018 to June 2020. The findings revealed that the 11 monitoring sites in the cities could be grouped into six clusters based on similar air pollution patterns. Overall, this study provides valuable insights that can inspire policymakers and stakeholders involved in air quality management to implement changes in environmental policies. By targeting pollution sources, it is possible to mitigate the harmful effects of air pollutants.