EDITORIAL: The Effects of COVID-19 Restrictions on Air Pollution are Highly Complex

Responses to the COVID-19 pandemic around the globe upended our daily lives in many ways. Many of us travelled less for work and for leisure and spent more time indoors at home. In this report, Tom Jefferson, Carl Heneghan and Jon Brassey show that one important effect of these changes was a sharp, albeit short-lived, reduction in many types of air pollution. Further, these improvements occurred in many of the world’s most populous cities.

In one sense, the results indicate the extent to which air quality can be altered by drastic changes in human activity. In another sense, however, the fleeting nature of these changes show how persistent air pollution is. Even as much of our lives have not returned to pre-pandemic “normal”, air pollution did as soon as the most draconian restrictions were lifted. And of course, even these temporary reductions came at a steep price.

As the report notes, the details are essential for understanding what these changes mean for people’s health. First, concentrations of ambient ozone actually increased on average during the restrictions, even as those of other dangerous pollutants like small particulates (PM_2.5) fell. Ozone and PM_2.5 both cause asthma and heart attacks, so the net effect of these changes is unknown.

Second, the link between these changes in pollution and changes in human health is uncertain due to the complexities of the “concentration response” functions. That is, the effect of any change in pollution on people’s health depends on the level of pollution and the duration of that change, among other things. While the changes in air pollution documented here were for several months, many of the studies summarized in the report assess only the effects of a change over 24 hours. It’s unlikely that the estimates of the daily effects can simply be scaled up to monthly effects.

Third, the changes were uneven, ranging from quite modest and remaining at very unhealthy levels in some places like Beijing, to unprecedented large reductions in places like Singapore. These differences, coupled with large differences in the effects of pollution across people by age and comorbidities, make it clear that the effects on health are likely to be quite uneven across geographic areas and across the global income distribution.

Fourth, the studies in the review examined outdoor air pollution. Steep declines in time spent outdoors were seen in nearly every country in March 2020 due to lockdown policies. Unfortunately, indoor air pollution is often far worse than outdoors. In fact, the WHO estimates that indoor air pollution kills more people each year than COVID-19 did in 2020. So even while the air outside improved across many measures, it may be that the air that people breathed, and subsequently their health, actually worsened. In fact, studies that fail to account for the differences between outdoor air quality and the quality of air that people actually breathe tend to substantially underestimate the health consequences of air pollution.

Finally, people sought out much less medical care during the pandemic. This means that reductions in emergency room and other treatments for asthma or cardiovascular events are likely to overstate the lessened burden of disease from any improvements in air quality. As with other studies of the overall effects of pandemic responses, excess mortality, rather than health care utilization, is likely to be the most insightful outcome to study.

We are grateful to the authors of both this report and the underlying studies for highlighting these collateral benefits to our environment. Even as we seek to understand the effects of pandemic responses on air pollution, additional research is emerging in parallel. In this parallel work, research is finding that airborne PM_2.5 may increase transmission of the SARS-CoV-2 virus and severity of COVID-19 symptoms. If so, the reductions in air pollution may have been more beneficial to people’s health than pre-pandemic estimates would indicate.

Jonathan Ketcham, PhD, is the Earl G. and Gladys C. Davis Distinguished Research Professor in Business in the W.P. Carey School’s Department of Economics at Arizona State University and a member of the Collateral Global editorial board.

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