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Study provides way to more accurately measure impact of COVID-19 response on air pollution

Published on September 8, 2020

A view of Seattle's typically busy freeways with very few vehicles, due to working from home and social distancing mandates.
Far fewer people are driving on Seattle's typically busy freeways due to working from home and social distancing mandates. Image Credit: Pxfuel. DMCA

Stay-at-home orders issued in Seattle in response to COVID-19 led to a significant drop in some of the most harmful air pollutants to human health, according to a novel method used by the University of Washington School of Public Health.

The researchers developed a new method to account for any differences in weather conditions – such as changes in wind speed and direction, temperature or humidity – that were observed during the study period and that could influence results. Study authors say “urban traffic-related air pollutant levels could be completely different in scenarios whether meteorology was adjusted for or not,” according to the paper published online July 28 in a special issue on COVID-19 for the journal Science of the Total Environment.

“This study found that the variation in weather conditions significantly confounded the effects of the COVID-19 shutdown on ambient air quality in urban Seattle,” said corresponding author Jianbang Xiang, a postdoctoral research fellow in the Department of Environmental & Occupational Health Sciences at the UW School of Public Health. “It suggests the need for fully adjusting for weather conditions in future studies examining the impacts of social and economic interventions on air pollution.”

After fully adjusting for weather, the study showed that the COVID-19 response in Seattle was associated with a 7% decrease in total ultrafine particles and a 2% decrease in fine particles, or PM 2.5, in the city. In contrast, results of the direct data comparison (without adjusting for weather) showed that PM 2.5 levels decreased by 33% and that there were no significant changes in levels of ultrafine particles.

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