Improved understanding of the sources of air pollution that are most harmful could aid in developing

more effective measures for protecting human health. The Denver Aerosol Sources and Health (DASH)

study was designed to identify the sources of ambient fine particulate matter (PM2.5) that are most

responsible for the adverse health effects of short-term exposure to PM2.5. Daily 24-h PM2.5 sampling

began in July 2002 at a residential monitoring site in Denver, Colorado, using both Teflon and quartz filter

samplers. Sampling is planned to continue through 2008. Chemical speciation is being carried out for

mass, inorganic ionic compounds (sulfate, nitrate and ammonium), and carbonaceous components,

including elemental carbon, organic carbon, temperature-resolved organic carbon fractions and a large

array of organic compounds. In addition, water-soluble metals were measured daily for 12 months in

2003. A receptor-based source apportionment approach utilizing positive matrix factorization (PMF) will

be used to identify PM2.5 source contributions for each 24-h period. Based on a preliminary assessment

using synthetic data, the proposed source apportionment should be able to identify many important

sources on a daily basis, including secondary ammonium nitrate and ammonium sulfate, diesel vehicle

exhaust, road dust, wood combustion and vegetative debris. Meat cooking, gasoline vehicle exhaust and

natural gas combustion were more challenging for PMF to accurately identify due to high detection limits

for certain organic molecular marker compounds. Measurements of these compounds are being

improved and supplemented with additional organic molecular marker compounds. The health study

will investigate associations between daily source contributions and an array of health endpoints,

including daily mortality and hospitalizations and measures of asthma control in asthmatic children.

Findings from the DASH study, in addition to being of interest to policymakers, by identifying harmful

PM2.5 sources may provide insights into mechanisms of PM effect.