Fine Particulate Air Pollution and Mortality in 20 U.S. Cities

Abstract

Samet et al. (Dec. 14 issue)¹ provide compelling, additional evidence of the link between outdoor air pollution — respirable particulate matter less than 10 μm in aerodynamic diameter (PM₁₀), in particular — and mortality. One perplexing finding, however, is the observed associations between outdoor ozone levels and mortality. These were marginally significant and positive during the summer but significant and negative during the winter. The authors suggest that the associations in the summer may reflect the higher levels of ozone during these months, but they fail to address the significance of the negative associations in the winter.