Comparison of indoor/outdoor carbon content and time resolved PM concentrations for gas and biomass cooking fuels in Nogales, Sonora, Mexico

A case study designed to investigate indoor and outdoor air quality in naturally ventilated homes near the US-Mexico border was conducted in Nogales, Sonora, Mexico from 14–30 March 2009. To better understand resident’s actual exposure to various sizes of particulate matter (PM), we compare measured concentrations in homes using different household stove cooking fuels (gas versus biomass) and investigate the spatial distribution of outdoor PM. Data from two home locations, one with a gas stove and one with both biomass and gas stoves are evaluated. In each home, continuous PM concentrations were sampled over a range of particle sizes. Indoor and outdoor concentration measurements were facilitated using a valve switching system. PM2.5 was also sampled on quartz filters located inside and outside of the two homes for carbon analysis. This paper will present a subset of the field data to compare time resolved indoor PM concentrations and carbon content for the two homes; specifically, comparing cooking versus non-cooking time periods. Results indicate that indoor elemental carbon concentrations are dominated by indoor sources during biomass burning, and outdoor sources at all other times. The data indicate that the influence of indoor sources on organic carbon concentrations increases during both gas and biomass stove use; this information is correlated to continuous indoor PM concentrations and home activities. The mean 24 h indoor PM10 concentration was 408 μg m−3 for the gas stove home and 648 μg m−3 for the home with biomass and gas stoves, while the outdoor concentrations were 609 μg m−3 and 381 μg m−3, respectively. The average 24 h PM10 Indoor/Outdoor ratio was 0.71 for the gas stove home and 1.79 for the home with both gas and biomass stoves. These ratios should be interpreted with caution as they appear to underestimate the indoor source contribution due to high outdoor PM levels.