The Effects of the COVID-19 Pandemic on Air Pollution: A Systematic Review

The efforts to reduce COVID-19 transmission could significantly affect pollution and weather in most parts of the world due to the reduction of industrial activities and road transport. Hence, this systematic review aimed to assess the effects of the COVID-19 pandemic on air pollution. The keywords were searched in the online databases of Scopus, PubMed, and Cochrane. We applied the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). Generally ambient air pollutants (PM2.5, PM10, NO2, NOX, NO, SO2, CO, black carbon, BTX (benzene, toluene, and Xylene), NH3, HCHO, PAHs, CH4, Solid Waste, UFPs (Ultrafine particle, ≥115.5 nm)) decreased significantly during lockdown period due to restricted human activities. Noteworthy, controversial findings have been reported concerning O3 levels; most studies, especially in East Asia, reported enhancement in the levels of O3, which was mainly attributed to meteorology factors. Although the COVID-19 pandemic caused a global health crisis, the improvement in worldwide air quality status was significant. Generally, pollutants generated by industrial activities were observed to be significantly reduced during lockdowns.