In population exposure studies, personal exposure to PM is typically measured as a 12- to 24-hr integrated mass concentration. To better understand short-term variation in personal PM exposure, continuous (1-min averaging time) nephelometers were worn by 15 participants as part of two U.S. Environmental Protection Agency (EPA) lon-gitudinal PM exposure studies conducted in Baltimore County, MD, and Fresno, CA. Participants also wore iner-tial impactor samplers (24-hr integrated filter samples) and recorded their daily activities in 15-min intervals. In Bal-timore, the nephelometers correlated well (R 2 = 0.66) with the PM 2.5 impactors. Time-series plots of personal nephelometer data showed each participant's PM expo-sure to consist of a series of peaks of relatively short dura-tion. Activities corresponding to a significant instrument response included cooking, outdoor activities, transpor-tation, laundry, cleaning, shopping, gardening, moving between microenvironments, and removing/putting on the instrument. On average, 63-66% of the daily PM ex-posure occurred indoors at home (about 2/3 of which occurred during waking hours), primarily due to the large amount of time spent in that location (an average of 72- 77%). Although not a reference method for measuring mass concentration, the nephelometer did help identify PM sources and the relative contribution of those sources to an individual's personal exposure.
Howard-Reed, C., Rea, AW., Zufall, MJ., Burke, JM., Williams, RW., Suggs, JC., ... Kwok, R. (2000). Use of a continuous nephelometer to measure personal exposure to particles during the U.S. Environmental Protection Agency Baltimore and Fresno panel studies. Journal of the Air & Waste Management Association, 50(7), 1125-1132.