Hierarchical Models and Statistical Issues in Health Effects of Ambient Airborne Particulate Matter

Despite trends showing improvements in air quality over the past two decades, there is growing concern about the health effects of particulate matter, even at levels below National Ambient Air Quality Standards (NAAQS). Epidemiological studies have shown a consistent effect of PM10 (particulate matter with an aerodynamic diameter less than 10 microns) on elderly mortality, with elevated risks for sub-populations with cardio-vascular disease or respiratory illness. Based on accumulating evidence linking health effects to ambient airborne particulate matter, the U.S. Environmental Protection Agency in 1997 promulgated revised, stricter air quality standards for particulate matter air pollution. For data from the 20 largest U.S. cities, Dominici et al. (2000) found that a 10µg/m3 increase in PM10 on the current day was associated with a 0.05 to 0.92 percent increase in elderly mortality. While many epidemiological studies have found statistically significant effects across many areas of the country, there remains considerable uncertainty regarding the health risk associated with particulate matter at levels below the National Ambient Air Quality Standards, and in particular, with the effect of fine particles less than 2.5 micrometers in diameter, PM2.5. In 1998, the National Research Council identified ten priorities for particulate matter research for setting regulator