Brief exposures to fine particulate matter (PM2.5) and seasonal ozone are affiliated with greater mortality risks, according to a study published in JAMA.

Qian Di, MS, of the Department of Environmental Health at Harvard T.H. Chan School of Public Health in Boston, and associates conducted a series of studies, from January 2000 to December 2012, to measure short term PM2.5 exposure and ozone and their effects on mortality. The investigation included all Medicare patients residing in 39,182 zip codes of the continental US.

Confirmed and published models predicting air pollution based on chemical transfer, land usage, and satellite remote sensing data were used to predict daily levels of PM2.5 and ozone in 1-km x 1-km grids. Predictions from these grids were used to determine daily exposures per zip code.

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The researchers used a time window, defined as the “warm-season” (start of April until the end of September), to study the relation between ozone and mortality.

Case days were reported dates of death, while control days were chosen for each case day. Control days were the same day of the week as the associated case day (before and after the case day) and only in the same month.

At that start of the investigation, death rates were 137.33 for the whole year and 129.44 for the warm-season.

During the course of the study, the researchers reported 22 million case days and more than 76 million control days. Of total case and control days, 93.6% had PM2.5 levels lower than 25µg/m3 (95.2% of deaths occurred during that time). Nearly 91% of the days had ozone levels less than 60 parts per billion (93.4% of deaths occurred during that time).

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“Short-term exposures to PM2.5 and warm-season ozone were significantly associated with increased risk of mortality,” the authors reported. “This risk occurred at levels below current national air quality standards, suggesting that these standards may need to be reevaluated.”


  1. Di Q, Dai L, Wang Y, et al. Association of short-term exposure to air pollution with mortality in older adults. JAMA. 2017 Dec 26. doi:10.1001/jama.2017.17923