Relationships of mortality with the fine and coarse fractions of long-term ambient PM10 concentrations in nonsmokers

In a cohort of 6338 California Seventh-day Adventists, we previously observed for males associations between long-term concentrations of particulate matter (PM) with an aerodynamic diameter less than 10 µm (PM 10 ) and 15-year mortality due to all natural causes (ANC) and lung cancer (LC) listed as underlying causes of death and due to nonmalignant respiratory disease listed as either the underlying or a contributing (CRC) cause of death. The purpose of this analysis was to determine whether these outcomes were more strongly associated with the fine (PM 2.5 ) or the coarse (PM 2.5–10 ) fractions of PM 10 . For participants who lived near an airport ( n =3769), daily PM 2.5 concentrations were estimated from airport visibility, and on a monthly basis, PM 2.5–10 concentrations were calculated as the differences between PM 10 and PM 2.5 . Associations between ANC, CRC, and LC mortality (1977–1992) and mean PM 10 , PM 2.5 , and PM 2.5–10 concentrations at study baseline (1973–1977) were assessed using Cox proportional hazards models. Magnitudes of the PM 10 associations for the males of this subgroup were similar to those for the males in the entire cohort although not statistically significant due to the smaller numbers. In single-pollutant models, for an interquartile range (IQR) increase in PM 10 (29.5 µg/m 3 ), the rate ratios (RRs) and 95% confidence intervals (CI) were 1.15 (0.94, 1.41) for ANC, 1.48 (0.93, 2.34) for CRC, and 1.84 (0.59, 5.67) for LC. For an IQR increase in PM 2.5 (24.3 µg/m 3 ), corresponding RRs (95% CI) were 1.22 (0.95, 1.58), 1.64 (0.93, 2.90), and 2.23 (0.56, 8.94), and for an IQR increase in PM 2.5–10 (9.7 µg/m 3 ), corresponding RRs (95% CI) were 1.05 (0.92, 1.20), 1.19 (0.88, 1.62), and 1.25 (0.63, 2.49), respectively. When both PM 2.5 and PM 2.5–10 were entered into the same model, the PM 2.5 estimates remained stable while those of PM 2.5–10 decreased. We concluded that previously observed associations of long-term ambient PM 10 concentration with mortality for males were best explained by a relationship of mortality with the fine fraction of PM 10 rather than with the coarse fraction of PM 10 .