Personal monitoring studies have indicated that environmental tobacco smoke ( ETS ) and cooking are major indoor particulate sources in residential and nonindustrial environments. Continuous monitoring of fine particles improves exposure assessment by characterizing the effect of time -varying indoor sources. We evaluated a portable nephelometer as a continuous monitor of indoor particulate levels. Simultaneous sampling with the nephelometer and PM 2.5 impactors was undertaken to determine the relationship between particle light scattering extinction coefficient ( sp ) and particle mass concentration in field and environmental chamber settings. Chamber studies evaluated nephelometer measurements of ETS and particles produced from toasting bread and frying foods. Field measurements were conducted in 20 restaurants and bars with different smoking restrictions, and in five residential kitchens. Additional measurements compared the nephelometer to a different mass measurement method, a piezobalance, in a well -characterized residence where various foods were cooked and ETS was produced. Since the piezobalance provides 2 -min average mass concentration measurements, these comparisons tested the ability of the nephelometer to measure transient particle concentration peaks and decay rate curves. We found that sp and particle mass were highly correlated ( R 2 values of 0.63 ± 0.98 ) over a large concentration range ( 5 ± 1600 g / m 3 ) and for different particle sources. Piezobalance and gravimetric comparisons with the nephelometer indicated similar sp vs. mass slopes ( 5.6 and 4.7 m 2 / g for piezobalance and gravimetric comparisons of ETS, respectively ) . Somewhat different sp vs. particle mass slopes ( 1.9 ± 5.6 m 2 / g ) were observed for the different particle sources, reflecting the influence of particle composition on light scattering. However, in similar indoor environments, the relationship between particle light scattering and mass concentration was consistent enough to use independent nephelometer measurements as estimates of short -term mass concentrations. A method to use nephelometer measurements to determine particulate source strengths is derived and an example application is described.

Numerous epidemiological studies have demonstrated associations between ambient combustion-source particulates and adverse health outcomes. In order to better understand exposure to particles, we evaluated a portable particle counter for its ability to measure short-term peaks in personal particle exposure associated with various activities, such as proximity to vehicular traffic. In a series of laboratory and field measurements, a hand-held particle counter was evaluated by collecting simultaneous filter samples of particulate matter less than 2.5 m (PM 2.5 ) using a personal monitor. Time activity information was collected using a Personal Digital Assistant (PDA) which allows for linking of exposure events and particle measurements with 1 min temporal resolution. Laboratory and field experiments comparing the particle counter with the personal PM 2.5 samples indicated low correlations (R 2 0.39) for all size ranges. Despite these rather poor correlations, field measurements collected during different commuting modes (walking/cycling, car, bus, subway) and in different microenvironments indicated the ability of the particle counter to measure short-term particle exposures, especially those associated with combustion sources. Stratifying the measured particle counts by proximity to different particle sources enabled us to identify activities/microenvironments which were associated with higher exposures. Outdoor particle counts were significantly higher than indoor counts for particles smaller than 5.0 m. Significantly elevated particle exposures were associated with proximity to environmental tobacco smoke (ETS), cooking emissions, wood smoke and with travel in vehicles powered with internal combustion engines.