Indoor/outdoor relationship and chemical composition of fine and coarse particles in the southern California deserts

The work presented in this paper examines the characteristics, chemical composition and relationship between indoor and outdoor particulate matter (PM) in the Coachella Valley, a unique desert area in southern California. Fine (0–2.5 μm) and coarse (2.5–10 μm) PM concentrations were measured concurrently indoors and outdoors in 13 residences during the winter and spring of 2000. Maximum outdoor PM penetration in indoor environments was expected during this period in the California deserts, as the mild climate minimizes the use of heating and/or air conditioning. Filter and impaction substrates were analyzed for mass, selected trace elements and metals, as well as elemental and organic carbon content (for fine PM only). Fine PM concentrations accounted, on average, for 74.3 (±11.0)% of the total PM10 concentrations indoors, whereas fine PM contributed to 61.3 (±13.1)% of the outdoor PM10 concentrations. The indoor-to-outdoor mass concentration ratios were 0.66 (±0.27) and 1.03 (±0.29), for coarse and fine PM, respectively. Chemical analysis of the filters revealed well-correlated indoor-to-outdoor concentrations of trace elements and metals in the fine PM mode, while lower correlations were obtained for the coarse PM mode. Elemental carbon concentrations indoors were 0.84 (±0.32) of those measured outdoors, whereas organic carbon concentrations indoors were on the average 77% higher than outdoors, presumably due to the contributions of indoor sources. Coarse PM concentrations based on mass, trace elements and metals showed similar trends, with the average indoor-to-outdoor concentrations varying from about 50% to 70%. Although the outdoor air of the specific study area has been traditionally considered to be rich in coarse particles, the results of this study suggest that indoor PM concentrations are still dominated by the contribution of fine particles.