Abstract
With the emergence of the COVID-19 pandemic, several governments imposed severe restrictions on socio-economic activities, putting most of the world population into a general lockdown in March 2020. Although scattered, studies on this topic worldwide have rapidly emerged in the literature. Hence, this systematic review aimed to identify and discuss the scientifically validated literature that evaluated the impact of the COVID-19 pandemic and associated restrictions on air quality. Thus, a total of 114 studies that quantified the impact of the COVID-19 pandemic on air quality through monitoring were selected from three databases. The most evaluated countries were India and China; all the studies intended to evaluate the impact of the pandemic on air quality, mainly concerning PM10, PM2.5, NO2, O3, CO, and SO2. Most of them focused on the 1st lockdown, comparing with the pre- and post-lockdown periods and usually in urban areas. Many studies conducted a descriptive analysis, while others complemented it with more advanced statistical analysis. Although using different methodologies, some studies reported a temporary air quality improvement during the lockdown. More studies are still needed, comparing different lockdown and lifting periods and, in other areas, for a definition of better-targeted policies to reduce air pollution.
Highlights
TchounwouAir pollution was estimated to cause 4.2 million premature deaths worldwide in 2016, according to estimations made by the World Health Organization (WHO) [1], reaching almost 5 million in 2017 according to the Health Effects Institute [2]
The present systematic review allowed us to summarise the information available in the literature that had been released about the impact of the COVID-19 pandemic on air quality
The most evaluated countries consisted of those highly affected by air pollution (India and China), even though at least one study was conducted in every continent
Summary
Due to its transmissibility and rapid spread worldwide, several governments imposed severe restrictions on both social life and economic activity, including stay-at-home orders, social distancing, mandatory quarantines and remote work and school. Those restrictions put most of the global population into a general lockdown on late March 2020 157 countries [4]), which temporarily reduced some of the major anthropogenic emission sources of air pollution and, resulted in marked air quality improvements worldwide [5] Those measures were temporary and possessed a high socioeconomic impact, they were both a global and local-scale unique opportunity to evaluate the effectiveness of some short-term measures to reduce air pollution in real-world. Understanding the effects of the COVID-19 pandemic on air quality is a unique opportunity to define better targeted short and long-term policies to ameliorate the air quality, derived from the restrictions imposed by the governments
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