The short-term association of selected components of fine particulate matter and mortality in the Denver Aerosol Sources and Health (DASH) study
Associations of short-term exposure to fine particulate matter (PM2.5) with daily mortality may be due to specific PM2.5 chemical components.
Objectives: Daily concentrations of PM2.5 chemical species were measured over five consecutive years in Denver, CO to investigate whether specific PM2.5 components are associated with daily mortality.
Methods: Daily counts of total and cause-specific deaths were obtained for the 5-county Denver metropolitan region from 2003 through 2007. Daily 24-hour concentrations of PM2.5, elemental carbon (EC), organic carbon (OC), sulfate and nitrate were measured at a central residential monitoring site. Using generalized additive models, we estimated relative risks (RRs) of daily death counts for daily PM2.5 and four PM2.5 component concentrations at day lag 0 through 3, while controlling for longer-term time trend and meteorology.
Results: RR of total mortality for an inter-quartile increase in PM2.5 distributed over 4 days was 1.012 (95% confidence interval: 0.999, 1.025); RRs for EC and OC were larger (1.024 [1.005, 1.043] and 1.020 [1.000, 1.040], respectively), whereas those for sulfate and nitrate were much smaller. We generally did not find associations with total cardiovascular and respiratory mortality. However, there were associations with ischemic heart disease mortality at day lag 3 or distributed over 4 days. In addition, cancer mortality was strongly associated with all four PM2.5 components, particularly for EC and OC, reflecting a pattern of mortality displacement.
Conclusion: PM2.5 components from combustion sources were more strongly associated with daily mortality than were secondary inorganic aerosols, especially in a very frail and susceptible subpopulation.