The impact of COVID-19 lockdown on air pollution in Europe and North America: a systematic review

Abstract

Background Multiple studies report reductions in air pollution associated with COVID-19 lockdowns. Methods We performed a systematic review of the changes observed in hazardous air pollutants known or suspected to be harmful to health, including nitrogen dioxide (NO2), nitrogen oxides (NOx), carbon monoxide (CO), sulfur dioxide (SO2), ozone (O3) and particulate matter (PM). We searched PubMed and Web of Science for studies reporting the associations of lockdowns with air pollutant changes during the COVID-19 pandemic in Europe and North America. Results One hundred nine studies were identified and analyzed. Several pollutants exhibited marked and sustained reductions. The strongest was NO2 (93% of 89 estimated changes were reductions) followed by CO (88% of 33 estimated pollutant changes). All NOx and benzene studies reported significant reductions although these were based on fewer than 10 estimates. About three-quarters of PM2.5 and PM10 estimates showed reductions and few studies reported increases when domestic fuel use rose during COVID-19 lockdowns. In contrast, O3 levels rose as NOx levels fell. SO2 and ammonia (NH3) had mixed results. In general, greater reductions appeared when lockdowns were more severe, as well as where baseline pollutant levels were higher, such as at low-elevation and in densely populated areas. Substantial and robust reductions in NO2, NO, CO, CO2, PM2.5, PM10, benzene and air quality index pollution occurred in association with COVID-19 lockdowns. O3 levels tended to increase, while SO2 and NH3 had mixed patterns. Conclusions Our study shows the profound impact of human activity levels on air pollution and its potential avoidability.

The Effect of the COVID-19 Pandemic on Environmental Health (Two Sides of the Same Coin): A Systematic Review

“…68 Based on the results of a systematic review by Bakola et al (2022), several air pollutants, including NO 2 , NO, PM2.5, PM10, CO, carbon dioxide (CO 2 ), benzene, black carbon, and air quality index (AQI)) related to the quarantine of COVID-19, showed a significant and strong decrease. 69…”

“…Studies have reported a reduction in pollutant concentrations during quarantine compared to the same period in previous years and even more robustly with historical data of more than 5 years. 68 Based on the results of a systematic review by Bakola et al (2022), several air pollutants, including NO 2 , NO, PM2.5, PM10, CO, carbon dioxide (CO 2 ), benzene, black carbon, and air quality index (AQI)) related to the quarantine of COVID-19, showed a significant and strong decrease. 69 According to the results of a systematic review study by Faridi et al, 70 in 2021, quarantine measures related to the COVID-19 epidemic significantly reduced the concentration of PM2.5, NO 2 , PM10, SO 2 , and CO globally.…”

“…68 Based on the results of a systematic review by Bakola et al (2022), several air pollutants, including NO 2 , NO, PM2.5, PM10, CO, carbon dioxide (CO 2 ), benzene, black carbon, and air quality index (AQI)) related to the quarantine of COVID-19, showed a significant and strong decrease. 69 According to the results of a systematic review study by Faridi et al, 70 in 2021, quarantine measures related to the COVID-19 epidemic significantly reduced the concentration of PM2.5, NO 2 , PM10, SO 2 , and CO globally. Apart from measuring pollutants at ground stations, studies using satellite data have confirmed the results obtained with ground-level measurements and found that AQI improved during the quarantine period.…”

“…A higher decrease was observed mainly for industrial areas. 71 Several mechanisms have been reported to significantly reduce pollutant levels: reducing people's driving and public transportation, 69,71 reducing or stopping the activity of industries and factories, 69 and reducing energy consumption 68 ; A remarkable point is that, in the case of some pollutants such as ozone, different results have been reported. Based on the results of the systematic review by Faridi et al 70 (2021), Silva et al 68 (2022), and Bakula et al 69 (2022), O 3 concentration has increased compared to the conditions before COVID-19.…”

“…71 Several mechanisms have been reported to significantly reduce pollutant levels: reducing people's driving and public transportation, 69,71 reducing or stopping the activity of industries and factories, 69 and reducing energy consumption 68 ; A remarkable point is that, in the case of some pollutants such as ozone, different results have been reported. Based on the results of the systematic review by Faridi et al 70 (2021), Silva et al 68 (2022), and Bakula et al 69 (2022), O 3 concentration has increased compared to the conditions before COVID-19. Various reasons for the increase in O 3 have been reported: decrease in NO and increase in solar radiation, 68 decrease in the titration of O 3 by NO X due to a significant decrease in local emission sources of NO X , possible increase in solar activity level due to decrease in PM2.5, and increase in the number of Hydroperoxyl radicals (HO 2 ) as a mediator to increase ozone production.…”