Use of a continuous nephelometer to measure personal exposure to particlesduring the US Environmental Protection Agency Baltimore and Fresno panel studies

In population exposure studies, personal exposure to PM is typically measur ed as a 12- to 24-hr integrated mass concentration. To better understand sh ort-term variation in personal PM exposure, continuous (1-min averaging tim e) nephelometers were worn by 15 participants as part of two U.S. Environme ntal Protection Agency (EPA) longitudinal PM exposure studies conducted in Baltimore County, MD, and Fresno, CA. Participants also wore inertial impac tor samplers (24-hr integrated filter samples) and recorded their daily act ivities in 15-min intervals. In Baltimore, the nephelometers correlated wel l (R-2 = 0.66) with the PM2.5 impactors. Time-series plots of personal neph elometer data showed each participant's PM exposure to consist of a series of peaks of relatively short duration. Activities corresponding to a signif icant instrument response included cooking, outdoor activities, transportat ion, laundry, cleaning, shopping, gardening, moving between microenvironmen ts, and removing/putting on the instrument. On average, 63-66% of the daily PM exposure occurred indoors at home (about 2/3 of which occurred during w aking hours), primarily due to the large amount of time spent in that locat ion (an average of 72-77%). Although not a reference method for measuring m ass concentration, the nephelometer did help identify PM sources and the re lative contribution of those sources to an individual's personal exposure.