Intake Fractions for Volatile Organic Compounds in Two Occupied California Residences

Experimental estimates of residential intake fractions for indoor volatile organic compound (VOC) releases are scarce. We evaluated individual intake fractions (iF(i), mass inhaled by an individual per unit mass emitted) using approximately five months of time-resolved VOC measurements acquired at two residences. First, we directly estimated iF(i) using inert tracer gases that were released at fixed rates. Tracer gas iF(i) values were generally consistent between occupants and comparable across seasons. Furthermore, iF(i) for sources released on different floors of a residence were statistically indistinguishable, suggesting that source location within the living space was not strongly influential. Emissions from living space sources (iF(i) similar to 0.3% = 3000 ppm) contributed to occupant exposures at rates 2-4 times higher than crawl space sources (iF(i) similar to 1000 ppm) and greater than 40 times higher than attic sources (iF(i) < similar to 70 ppm). Second, we indirectly estimated iF(i) for 251 VOCs using net emission rates estimated by indoor-outdoor material balance. Although emission patterns varied between compounds, all VOC-specific iF(i) estimates were clustered near the values of the living space tracer gases. These experimental observations substantiate the theoretical expectation that iF(i) values are largely independent of analyte characteristics, a useful simplification for exposure assessments.