Assessment of indoor fine aerosol contributions from environmental tobacco smoke and cooking with a portable nephelometer

Abstract

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 (σ_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 σ_sp and particle mass were highly correlated (R² values of 0.63–0.98) over a large concentration range (5–1600 µg/m³) and for different particle sources. Piezobalance and gravimetric comparisons with the nephelometer indicated similar σ_sp vs. mass slopes (5.6 and 4.7 m²/g for piezobalance and gravimetric comparisons of ETS, respectively). Somewhat different σ_sp vs. particle mass slopes (1.9–5.6 m²/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.