Linking health effects to PM components, size, and sources.

A number of physicochemical factors contribute to the adverse cardiopulmonary effects associated with exposure to ambient PM. It has become increasingly clear that mass concentration alone may not be the best indices for associating health effects with exposure to PM. Recent epidemiology and animal toxicology data have examined the role of particle size and components on cardiopulmonary effects. In addition, collaborative efforts in North America and Europe have examined the in vitro and in vivo toxicity of size-fractionated particles collected in a variety of urban and rural sites. The ability of these latter studies and other investigations to develop source apportionment findings will become increasingly important for policy makers and regulators in their deliberations.