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 (PM(2.5)) that are most responsible for the adverse health
effects of short-term exposure to PM (2.5). Daily 24-hour PM(2.5) 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 PM (2.5) source contributions for each 24-hour 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 PM(2.5) sources
may provide insights into mechanisms of PM effect.