Issues in human particulate exposure assessment: Relationship between outdoor, indoor, and personal exposures

The recent review of the National Ambient Air Quality Standard for particul ate matter and the resultant new health-based PM2.5 standard was in part mo tivated by findings from epidemiological studies. These studies reported si gnificant associations between adverse health effects and concentrations of ambient particulate matter at levels below the previously existing PM10 st andard. Interpretation of these results has been hindered by our relatively poor understanding of the relationship between personal exposures and conc entrations in the indoor and outdoor environments. Individuals spend the ma jority of their time in indoor environments. Therefore, it is important to understand where and how they may be exposed to the contaminants which may be causing the health effects, and which activities place them at a higher risk of exposure to these agents. In addition, since particulate matter is a complex mixture of contaminants, further research is required to examine its formation process, sources, composition, and health effects. Without an improved scientific understanding of these issues, it is difficult to asse ss whether the new PM2.5 standard will be implemented, and if so, whether i t can be adequately protective of public health.