This report summarizes the major accomplishments of the U.S. Environmental Protection Agencys Particulate Matter (PM) Research Program achieved since 1997. Among the most notable achievements is that scientists have quantitatively established that exposure to ambient particulate matter (PM) is associated with morbidity and mortality. Signi.cant progress has also been made in understanding the in.uence of PM size and composition on unwanted health outcomes, in uncovering the biological mechanisms which link PM exposure to adverse health outcomes, and in discovering the human characteristics which increase susceptibility to adverse health outcomes. Additionally, advances in PM science have provided information about the deposition and fate of particulates in the respiratory tract as well as about the sources of particulate air pollution and about the atmospheric processes that in.uence PM chemistry and transport. These research outcomes provide the basis for scienti.cally defensible regulatory actions and support the Agencys ongoing mission of ensuring that the air in every American community is safe and healthy to breathe.

"EPA 600/R-04/058"--T.p. "July 2004"--T.p. Includes bibliographical references.