Project at a Glance

Title: Residential microenvironmental and personal sampling project for exposure classification.

Principal Investigator / Author(s): Avol, Ed

Contractor: University of Southern California

Contract Number: 92-317

Research Program Area: Health & Exposure

Topic Areas: Health Effects of Air Pollution, Indoor Air Quality, Modeling, Toxic Air Contaminants


This project sought to gather exposure assessment information for improved modeling of human air pollution exposures. Air monitors were deployed during 247 visits (1126 initial visits, 121 second visits) to homes across four Southern California communities. Home selection was based on concurrent participation in a cross-sectional air pollution health effects study, air conditioning type, and community location. Measurements were performed between February and November 1994, to observe potential differences in seasonal patterns of home operation. Sampling included administration of three survey questionnaires to document housing and human activity factors of potential importance and simultaneous indoor/outdoor air sample collection over a 24hr period. Measurements included ozone, particulate matter (PM10 and PM2.5), formaldehyde, and house air exchange rate in a variable number of homes. A twelve-home pilot study also provided two-week integrated data about indoor/outdoor levels of airborne acids and fine particle chemistry.

Indoor ozone was typically low (median of 5.6 ppb); the median outdoor ozone concentration was 34 ppb. The indoor/outdoor (I/O) ratio (median value of 0.20) displayed a distinct seasonality, with the ratio increasing during summer months. Indoor PM2.5 measurements (median of 13.7 g/m3) tended to be higher that outdoor levels (median outdoor PM2.5 of 10.7g/m3, median I/O PM2.5 ratio of 1.10), reflecting the presence of indoor sources. A strong seasonality of either PM2.5 , or the PM2.5, I/O ratio was not observed, but this may be due more to the time period of field observations (late June through November only) than to the lack of a seasonal PM relationship across the year. Median observed PM10 levels were 32.9 g/m3 indoors and 29 g/m3 outdoors, with a median I/O ratio of 1.05. Several homes were observed with indoor levels exceeding 100g/m3. No strong PM10 seasonality was observed, which may be an effect of the sampling period. Indoor formaldehyde levels were low (median value of 10g/m3), but were higher than observed outdoor levels (median of 3.2 g/m3). No formaldehyde seasonality was observed. Median air exchange rate (AER) were calculated to be 0.7hr-1, using a corrected home volume method that accounted for space-occupying objects in the home (this approach tended to increase observed AER estimates by about 10%). AER tended to be lower during the spring and fall than during the summer. Summertime AERs were also more variable.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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