Research Note 94-14 - Indoor air pollutants

No. 94-14
August 1994
California Environmental Protection Agency Brief Reports to the Scientific and Technical
Air Resources Board Community

Research Division, John R. Holmes, Ph.D., Chief P.O. Box 2815, Sacramento CA 98512

California Indoor Exposure Database

This study produced a database for evaluating Californians' long-term indoor and personal exposures to 30 volatile organic compounds (VOCs). The database consolidates data sets from six field studies that obtained VOC measurements and questionnaire information from residents of several California cities. Statistical analyses using the new database indicate that indoor and personal exposures are higher in winter than in summer for common VOCs. In addition, exposure levels correlate positively with the presence of indoor emission sources and human activities in the home.


California law requires the Air Resources Board (ARB) to assess indoor exposures to candidate toxic air contaminants. Six field studies of over 300 homes in three regions of California have provided important indoor and personal exposure data for 30 toxic pollutants. The studies include the 1984 and 1987 California Total Exposure Assessment Methodology (TEAM) studies, plus a 1990 ARB study. The locations and dates of the studies were:
  • Los Angeles County - February-March 1984
  • Los Angeles County - May-June 1984
  • Pittsburg/Antioch (Contra Costa County) - June 1984
  • Los Angeles County - January-February 1987
  • Los Angeles County - June-July 1987
  • Woodland (Yolo County) - May-June l990
The designs of the five TEAM studies were basically the same. The Woodland study was different from the first five studies in having 24-hour chemical sampling periods instead of two 12-hour periods. However, the same research team conducted all the studies and used virtually the same methods for sample collection and chemical analyses. Thus, data obtained from these field studies could reasonably be combined and analyzed to identify similarities and differences in exposures due to geographical location, seasonal variation, socioeconomic factors, the activities of the participants. and household characteristics. The main objective of this project was to consolidate the six data files into a database with uniform coding and format to facilitate further data analyses. Another objective was to perform selected statistical analyses to examine indoor exposure issues, and to illustrate types of additional analyses that could be performed in the future.
Results: The final report consists of two volumes. Volume 1 provides a brief description of the six California studies and documents the creation, structure, and content of the database. The database consists of five primary files and other auxiliary files. The primary files include:
  • Questionnaire data about household and personal characteristics, and data on activities, microenvironments, and presence of emission sources during the monitoring period.
  • Indoor and outdoor air concentration data and personal exposure data from consecutive 12-hour monitoring periods.
  • Indoor and outdoor air concentration data and personal exposure data for 24-hour monitoring periods.
  • Chemical concentration data from drinking water samples (1984 and 1987 studies only).
  • Chemical concentration data from exhaled breath samples (1984 and 1987 studies only).
Volume II of the report presents five types of data analysis to illustrate some of the important analyses that can be done with the database. The first analysis showed that a portion of the population is exposed to levels of volatile chemicals substantially higher than the average level. This observation is illustrated by the graph in Figure 1.

Figure 1
Typical Distribution of Personal Exposure to a Volatile Chemical

Also, exposures of active smokers to certain toxic VOCs were notably higher than those of nonsmokers, including nonsmokers exposed to environmental tobacco smoke. The second analysis examined differences in personal exposure levels among the different geographical areas. Results indicate that personal exposures to certain chemicals are higher in southern California than in northern areas of the State.

The third analysis compared the indoor levels of chemicals over time in homes that were sampled on more than one occasion. Indoor levels of five chemicals were significantly higher in winter than in summer. However, the indoor/outdoor ratios for those chemicals were generally the same for both seasons. Thus, the apparent seasonal differences in indoor levels may be largely due to changes in outdoor air concentrations. The fourth analysis examined relationships among concentration levels of different chemicals. Concentrations of chemicals in the outdoor air were more strongly associated with each other than they were in indoor or personal air microenvironments. This implies that chemicals are emitted from a greater variety of sources in indoor or personal air microenvironments than in outdoor air.

The fifth analysis, using linear models, identified and tested factors that may influence indoor air concentrations of chemicals. Several strong relationships were identified.

For example, tobacco smoking was strongly correlated with increased indoor benzene levels, and perchloroethylene and methyl chloroform levels were elevated in homes with dry-cleaned clothes. In addition, indoor benzene, o-xylene, and styrene levels were elevated in homes where gasoline-powered vehicles were kept in an attached garage.
Significance and Application: The database provides a unique ability to examine indoor exposures to VOCs because it includes data from over 300 homes in three different parts of the state and covers a variety of seasons. The self-contained database facilitates further in-depth analyses of California indoor exposure data and will provide additional information useful in assessing the public's exposures and health risk due to pollution of indoor air.
Related Projects: In addition to the six exposure studies mentioned in this database, the ARB has recently completed two similar projects for non-volatile toxic compounds. One project measured personal, indoor, and outdoor concentrations of PM10, phthalates, polycyclic aromatic hydrocarbons, and metals in a southern California city. The other project measured indoor and outdoor concentrations of polycyclic aromatic hydrocarbons and carbon monoxide in two northern California cities.

This research was conducted under contract with Research Triangle Institute (ARB Contract No: A133-187). Comments or questions can be directed to the contract manager, Steve Hui, by mail, FAX (916) 322-4357, phone (916) 323-1530, or e-mail.
Copies of the research report upon which this Note is based can be ordered from:
National Technical Information Service
5285 Port Royal Rd
Springfield VA 22161
Request NTIS No. PB94-138997
Title: Data Base Development and Data Analyses for California Indoor Exposure Studies, Vols. I and II
Authors: A. Clavton and R. Perritt