CG REPORT 4: Effects of COVID-19 Restrictions on Air Pollution
Reductions in the movement of people and industrial production during COVID restrictions resulted in lower levels of particulate matter (PM) of all sizes, Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2) and Carbon Monoxide (CO), pollutants that are associated with increased mortality. However, the window of observation of most studies ended in the late spring of 2020. Therefore, it is unclear whether lowering pollutant levels were sufficiently long to affect morbidity and mortality. In addition, studies indicated a return to pre-restriction levels shortly after restrictions were lifted.
The impact of COVID-19 restrictions on the global levels of environmental pollutants is likely to be beneficial. Lower levels of pollution observed during restrictions provide estimates for attainable pollutants that can benefit health and wellbeing.
Overall we rated the impact of COVID-19 restrictions on air pollution as substantial.
Restrictions on movement, activity and industrial production caused a dramatic increase in the quality of the air. Although perhaps too brief to show an effect on overall morbidity and mortality, the effects on health should not be underestimated. A significant body of evidence from systematic reviews shows long term air pollutants are associated with substantial wide-ranging adverse health effects, including increased mortality. Furthermore, high-quality evidence also indicates that short term exposure to many pollutants increases morbidity and mortality.
The studies show a consistent decrease in PM, NO2, SO2 and CO compared to the same period in previous years. These falls were usually accompanied by a rise in ozone levels, possibly because of more photosynthesis because of the absence of U.V. block.
The effects of restrictions on ambient air pollutants were heterogeneous across countries and within countries. Part of the reason is the substantial variation in pre-pandemic levels of pollutants, large-scale urbanization and economic development in low and middle-income countries (LMICs), which led to significant disparities in air pollution exposure.
The beneficial effects of restrictions on pollution levels should be followed with long term longitudinal studies assessing whether the improvement in air quality is sustainable along with the repercussions on mortality, respiratory and cardiovascular pathologies. Changes in work patterns should be monitored to evaluate their impact on pollution levels. The results in this report suggest that strategies to minimise air pollution should be further enhanced.
Quality of Evidence
The quality of the evidence was judged to be moderate: future high-quality longitudinal studies are required to assess the long term sustainability of measures to reduce pollution independently from the imposition of restrictions. All studies were ecological before and after design. The observed effect sizes represent potent indicators of a real gain in air quality as their results are univocal. However, the lack of mapping of restrictions and their chronology of introduction makes the assessment of the advantages on pollution levels of different types of restrictions and their time windows impossible.