Human skin oils drive ozone chemistry in occupied house

Ozone pollution is a well-known health concern, but researchers understand less about how the highly reactive molecule behaves indoors in the complex environment of a home. Yingjun Liu of Peking University and coworkers now report that human skin oil drives ozone chemistry in an occupied home as the residents go about their lives (Proc. Natl. Acad. Sci. U.S.A. 2021, DOI: 10.1073/pnas.2018140118). “This is the first time these measurements have been made in an actual home under normal living conditions,” says Charles J. Weschler of Rutgers University, who worked on the study.

By continuously measuring the air in an Oakland, California, home using a proton-transfer-reaction time-of-flight mass spectrometer, the researchers detected volatile compounds known to result from ozone-initiated chemistry, especially products of reaction with squalene, a major lipid in human skin oils. The squalene reaction products were the dominant contributor to ozone-initiated chemistry even when the house was vacant, suggesting to the researchers that squalene on touched surfaces, clothing, and skin flakes in dust continues to react with ozone. During a party with about 15 guests, the squalene reaction products increased significantly.

Because the ozone and ozone reaction products were present at similar levels, scientists interested in ozone health effects need “to start thinking a little harder about whether these products could be as important as ozone and why,” says Allen H. Goldstein of the University of California, Berkeley, who worked on the study. The base ozone levels measured in the home over the 8-week campaign were a fraction of those outdoors at the time of the study and well below levels of concern. Because the ozone concentrations were so low, the researchers think the findings will be representative of many homes in the US.

“The one big limitation of this work is that their instruments weren’t tuned to detect some of the more toxic, oxidized molecules that might be produced” from indoor reactions with ozone, Delphine Farmer, who studies indoor chemistry at Colorado State University, writes in an email. “So unfortunately, we don’t have a handle on whether there are health implications of this finding or if it is merely fascinating chemistry.”