Assessment of indoor aerosols with an integrating nephelometer

A portable nephelometer was used to assess particulate levels inside and outside of homes with indoor air impacted by biomass combustion. Simultaneous sampling with PM10 and PM2.5 inertial impactors was undertaken to determine the relationship between particle light scattering coefficient (sigma sp) and particle mass concentration. Measurements were conducted in 22 homes in rural Mexico and in 6 homes in rural British Columbia, Canada. In both areas, biomass combustion resulted in high levels of fine particulates, mainly indoors in Mexico and outdoors in British Columbia. Comparisons were made between the average of the nephelometer sigma sp (unheated nephelometer inlet stream) and the measured particle mass (PM10 and PM2.5) during a defined sampling duration. The two measurements were highly correlated (r2 values of 0.79-0.96) over a wide range of particle mass concentrations (10-1600 micrograms/m3). A stronger correlation was observed for PM2.5 than for PM10. Colocated outdoor nephelometer and impactor measurements were poorly correlated (r2 = 0.50). Substantially different relationships were observed between the Mexico and British Columbia particulate, indicating the importance of particle composition and ambient conditions as factors affecting light scattering, even indoors. However, in a given series of similar indoor environments, the relationship between particle light scattering and mass concentration is stable enough to use independent nephelometer measurements as estimates of mass concentrations. The fast-response, continuous measurement, portability and datalogging capabilities of this nephelometer, combined with its ease of use, make this an important measurement tool to be used in conjunction with traditional filter sampling in the assessment of indoor particle levels and the evaluation of sources.