Particulate matter (PM) air pollution and health: regulatory and policy implications

Particulate matter (PM), an ambient air criteria pollutant, is a complex mixture of chemical agents in particles ranging from nanometer-sized molecular clusters to dust particles too large to be aspirated into the lung airways (>10 mu m in aerodynamic diameter). Although particle composition is known to affect health risks, our current health-based PM standards are limited to the mass concentrations within two specified size ranges (those below 2.5 mu m, which are largely attributed to combustion products, and those below 10 mu m, which includes mechanically generated dusts). Both size ranges have been associated with excess mortality and morbidity in numerous epidemiological studies. There is an urgent need for routine air monitoring data on components of the PM mass. Such data are needed to enable epidemiological studies that can define the roles of PM chemical components in causing adverse health effects in order to guide more targeted emission controls for the most hazardous components, thereby gaining public health benefits with the least impact on societal costs of emission controls.