PM2.5-Related Air Pollution Reduced, but Ozone Levels Need Improvement

Smog over New York City Skyline, air pollution
Smog over New York City Skyline, air pollution
Much of the United States has seen improvements in health effects from ambient levels of PM2.5; however, health effects from ozone levels have not improved.

Most of the United States has seen improvements in health effects in the last 10 years due to ambient levels of particulate matter less than 2.5 microns in aerodynamic diameter (PM2.5), according to a study published in the Annals of the American Thoracic Society. However, adverse health effects related to O3 have not improved significantly, and in many cities, they have actually increased.

This study included daily air pollution values from 2008 to 2017 from the Environmental Protection Agency Air Quality System for design value monitors. From these values, annual control and baseline datasets were created with a 24-hour PM2.5 metric, a 1-hour maximum O3 metric, an 8-hour maximum O3 metric, and a 24-hour mean O3 metric. The American Thoracic Society (ATS) /Marron Institute’s “Health of the Air” concentration-response functions were used in the study’s pollution strata. These matched rolling 3-year design value differences and PM2.5 levels recommended by the ATS: annual, 11 µg/m3; short-term, 25 µg/m3; and O3, 60 ppb. In regions with sufficient monitor data, health effects were estimated. Concentration-response relationships were used to determine the health effects, including mortality, major morbidity, and adversely impacted days of pollution levels.

In the United States between 2010 and 2017, annual excess mortality due to excessive air pollution decreased from around 12,600 deaths (95% CI, 5470-21,040) to 7140 deaths (95% CI, 2290-14,040). Lower PM2.5-related mortality is largely responsible for this improvement, as its rate decreased 8330 to 3260 annual deaths (~60%) during this time period. Meanwhile, O3-related mortality remained nearly constant, changing from 4270 to 3880 deaths per year. Of the 530 counties with valid PM2.5 design values, 78 did not meet concentrations recommended by the ATS, whereas of the 726 counties with valid O3 design values, 599 did not meet concentrations recommended by the ATS.

A limitation of this study is the exclusive investigation of health effects due to pollution above the levels recommended by the ATS.

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“Even maintaining current pollution levels will ultimately result in increasing numbers of mortalities and other health impacts as populations grow over time,” the researchers concluded. “As state and city leaders determine which policy decisions are best suited for reducing air pollution and keeping up with population growth, they can utilize “Health of the Air” data to target areas and design policies to best address those pollutants causing the greatest health impacts among their locales.”


Cromar KR, Gladson LA, Ewart G. Trends in excess morbidity and mortality associated with air pollution above ATS-recommended standards, 2008 to 2017 [published online May 21, 2019]. Ann Am Thorac Soc. doi:10.1513/AnnalsATS.201812-914OC