US EPA

Total human exposure to particulate matter (PM) may be divided into two major components: (1) exposure to ambient-source PM while outdoors plus exposure while indoors to ambient PM that has infiltrated indoors and (2) exposure to nonambient-source PM (due to indoor sources and personal activity or personal cloud sources). For epidemiology using small cohorts with measurements of individual health outcomes, it is desirable to know total, ambient, and nonambient exposures. For community time-series studies, in which ambient concentration is used as an indicator of ambient exposure, it would be useful to have an estimate of the average community ratio of ambient exposure to ambient concentration (alpha), the average nonambient exposure, and the distributions of both.

Wilson Jr., W E. AND M. Brauer. Methods To Estimate The Ambient And Nonambient Components Of Total Personal Exposure To Particulate Matter. Presented at International Society of Exposure Assessment, Charleston, SC, November 4-8, 2001.