When people are out and about, they leave plumes of chemicals behind them—from both car tailpipes and the products they put on their skin and hair. In fact, emissions of siloxane, a common ingredient in shampoos, lotions, and deodorants, are comparable in magnitude to the emissions of major components of vehicle exhaust, such as benzene, from rush-hour traffic in Boulder, Colorado, according to a new CIRES and NOAA study. This work, published in the journal Environmental Science and Technology, is in line with other recent findings that chemical emissions from personal care products can contribute significantly to urban air pollution.
“We detected a pattern of emissions that coincides with human activity: people apply these products in the morning, leave their homes, and drive to work or school. So emissions spike during commuting hours,” said lead author Matthew Coggon, a CIRES scientist at the University of Colorado Boulder working in the NOAA Earth System Research Laboratory.
D5 Siloxane, short for decamethylcyclopentasiloxane, is added to personal care products like shampoos and lotions to give them a smooth, silky feeling. Siloxane belongs to a class of chemicals called volatile organic compounds (VOCs); once applied, they evaporate quickly. In the air, sunlight can trigger those VOCs to react with nitrogen oxides and other compounds to form ozone and particulate matter—two types of pollution that are regulated because of their effects on air quality and human health.
Coggon and his colleagues measured VOCs from the roof of NOAA’s Earth System Research Laboratory in December, 2015 and January, 2017, and from a mobile laboratory driving around Boulder in February, 2016. Among other measurements, they tracked the concentrations of traffic-related compounds, including benzene, commonly used as a marker of vehicle exhaust, during rush hour.
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