Classroom VOC Contaminants

COEH investigator William Nazaroff led a team measuring VOC emissions in a university classroom. Researchers found that human-emitted VOCs were the dominant source contributing 57 percent of total emissions. And, similar to early childhood environments, personal care products were ranked highest among the species detected, according to the paper published in the December 6, 2016, issue of Environmental Science and Technology

Ventilation supply air was the second most important source accounting for 35 percent of the VOCs detected. Indoor non-occupant emissions, such as furniture and floor coverings, accounted for only 8 percent of total emissions.

Researchers measured VOCs, carbon dioxide (CO2), and ozone (O3) in a classroom and its ventilated air supply over a two-week period. A total of 18 classes were conducted during this interval. The team apportioned the source rate of each measured VOC into one of three categories – supply air, human occupants and their belongings, and indoor sources from building materials and room furnishings. Data calculations took into account the periods when the classroom was unoccupied and also when the ventilation system was turned off overnight before resuming operation at 8:00 a.m.

Out of 220 VOC compounds measured, the six most abundant VOCs contributed 62 percent of the total, and the 20 most abundant accounted for 80 percent of the total. Three cyclic volatile methylsiloxanes (cVMS), including decamethycyclopentasiloxane (D5), octamethycyclotetrasiloxane (D4), dodecamethylcyclohexasiloxane (D6) accounted for roughly a third of total VOC concentrations. These compounds, also known as cylclomethicones, are common ingredients in personal care products, such as antiperspirants.

Also prominent were human metabolic emissions, such as isoprene, methanol, acetone, and acetic acid, according to study authors. Additional features contributing to emissions included human skin oil oxidation by ozone, producing compounds such as 4-oxopentanal (4-OPA) and 6-methyl-5-hepten-2-one (6-MHO). Researchers found the CO2 emission rates varied little across all classroom periods, as they predicted.

Few studies have explored the impact of humans on indoor air chemistry. Since we spend most of our time indoors, this study provides important characterization of the chemical composition of the air we breathe and also of the contribution of personal care products to indoor air quality.

The study was funded by the Alfred P. Sloan Foundation. The study team included postdoctoral scholar Xiaochen Tang, Associate Specialist Pawel K. Misztal, and Professor Allen H. Goldstein, all from UC Berkeley.

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