| The Relationship of Indoor, Outdoor and Personal Air (RIOPA) study was designed to investigate residential indoor, outdoor and personal exposures to several classes of air pollutants, including volatile organic compounds (VOCs), carbonyls and fine particles (PM2.5). Samples were collected from summer, 1999 to spring, 2001 in Houston (TX), Los Angeles (CA), and Elizabeth (NJ). Median indoor, outdoor and personal PM2.5 mass concentrations for these three sites were 14.4 mug/m3, 15.5 mug/m 3, and 31.4 mug/m3, respectively. Indoor and outdoor PM2.5 mass and species concentrations were used to calculate the contribution of outdoor sources to indoor PM2.5 concentrations using five approaches with increasingly accurate assumptions to investigate exposure errors: random component superposition approach, mass balance model approach, external mixture approach, sulfur tracer approach and robust regression approach. The robust regression approach takes into account variations in building construction, ventilation practices and particle size distributions, introducing home-to-home and day-to-day variations in P, k and air exchange rate. With increasing accuracy (from the most constrained RCS model to the most unconstrained Robust Regression model), the mean contribution of outdoor sources to the indoor PM2.5 mass concentration increased. More importantly from the standpoint of epidemiological measurement error, the bandwidth of this distribution increased from 22% (RCS), to 26% (mass balance), to 29% (external mixture) and 36% (robust regression). Positive matrix factorization, an advanced factor analysis, was used to find indoor and outdoor PM2.5 factors and infiltration factors for outdoor PM2.5 factors. Factors found corresponded to the major outdoor source types: secondary aerosol, soil, oil combustion/industry, and mobile sources. Major indoor source types are particles related to indoor combustion and indoor cleaning processes. A large fraction (40%∼60%) of the identified indoor PM 2.5 mass concentration was explained by outdoor factor contributions. This work suggested that primary combustion (FINF = 0.51) and secondary formation (FINF = 0.78) particles have larger infiltration factors than particles generated by mechanical forces (FINF = 0.04). Hence, the composition of ambient PM2.5 is different from PM2.5 of outdoor origin. |
