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Volatile Organic Compounds in Indoor Air
Volatile organic compounds (VOCs) may arise in indoor air from sources other than vapor intrusion, so the presence of a VOC is not necessarily proof that vapor intrusion is of concern.
Because of the potential for VOCs to exist in indoor air from multiple sources, it is often useful to compare indoor air measurements to concentrations that have been observed in buildings that are not known to be impacted by vapor intrusion, and which may be thought of as typical “background”.
Sources of Indoor Air Contamination
Information on common household products that cause measureable levels of VOCs in indoor air can be found in the National Institutes of Health Household Products Database.
Background Concentrations of VOCs in Indoor Air
EPA released a technical report in 2011 that compiles statistical information on background indoor air concentrations of VOCs from 15 indoor air studies conducted between 1990 and 2005.
- Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences (1990-2005): A Compilation of Statistics for Assessing Vapor Intrusion. (PDF) (67 pp, 812 K, About PDF) (EPA 530-R-10-001, June 2011)
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Comparing Site to Background
In performing a comparison of site levels to "background" or “ambient” levels, it is important to understand that both site levels and background levels are characterized by distributions, and that a comparison must be based on sound statistical techniques. Useful guidance for how to conduct statistical comparisons of site data to background includes:
- Guidance for Comparing Background and Chemical Concentrations in Soil for CERCLA Sites (PDF) (89 pp, 1.3 MB) OSWER 9285.7-41, September 2002
- Performance of Statistical Tests for Site Versus Background Soil Comparisons When Distributional Assumptions Are Not Met (PDF) (56 pp, 1.4 MB) EPA/600/R-07/020, March 2007
If the measured level of a chemical is not statistically higher than the level that would be expected for that chemical based on background levels, then it may be concluded that the site-related contribution for that chemical is sufficiently minor that further quantitative evaluation is not needed. If the chemical is observed to be present at a level higher than would otherwise be expected, then it is appropriate to retain that chemical for quantitative risk evaluation.
EPA's Indoor Air Quality (IAQ) Web page provides information and links to resources on sources of air pollution in homes and offices, and addressing indoor air quality in public and commercial buildings.