Indoor Air Background Concentrations of Volatile Organic Compounds ( <scp>VOCs</scp> ) in California Residences

Abstract A study was performed to measure typical “indoor air background” concentrations of volatile organic compounds (VOCs) in residential buildings in the state of California that were not known to be impacted by subsurface sources. A total of 57 buildings were sampled between February 2023 and February 2024, with one sample collected per building. The data set represents 38 different cities within the state of California. The samples were analyzed using the United States Environmental Protection Agency (EPA) Method TO‐15 (EPA 1999) in both full‐scan and Selected Ion Monitoring (SIM) modes. A total of 105 individual VOCs were reported for each sample. The overall data set is 5985 individual data points, with concentrations of target compound VOCs reported from less than the laboratory method reporting limit of 0.044 μg/m 3 (micrograms per cubic meter) to concentrations up to 14,000 μg/m 3 . Various VOCs were detected at concentrations above screening levels used in California and elsewhere in the United States, including Benzene, Naphthalene, Tetrachloroethene (PCE), and Trichloroethene (TCE). These compounds are often considered “risk drivers” in vapor intrusion (VI) studies, so their presence in background air at concentrations above screening levels may complicate such studies. Compared with previous, similar studies, this study is more comprehensive with a larger number of VOCs analyzed and with greater analytical sensitivity. Based on the professional backgrounds of the study group which included environmental professionals, regulatory officials, and attorneys, the authors opine that the results of this residential indoor air background study may be biased low relative to the general population. Therefore, the results of the Study are considered to reflect a conservative snapshot of indoor air background VOCs in California residences.