Indoor emissions and production of volatile organic compounds (VOCs) are of concern due to their harmful impacts on human health. Although significant progress have been made in understanding the sources and chemistry of VOCs in indoor environments during the past several decades, little is known about the role of humans in affecting indoor VOC chemistry. To address this issue, we conducted continuous measurements of VOCs in a classroom at the University of Colorado Boulder during 15 March to 10 May 2014. The classroom was both occupied and unoccupied during measurements, with peak occupancy at ~150. The ventilation rate for the class room was 5-6 h-1. A Proton Transfer Reaction Mass Spectrometer (PTR-MS) and a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer equipped with acetate/nitrate ion sources were deployed to characterize VOC classes with different chemical and physical properties. Our results show that many indoor VOCs are different from outdoor VOCs in their concentration, sources, and formation/emission mechanisms. VOCs produced from O3 oxidation of squalene, a major component in human skin lipids, were identified. O3 anti-correlated with occupancy, suggesting that reactions on occupant surfaces may be an important source of secondary indoor VOCs. Positive matrix factorization analysis of the PTR-MS measurements results in three main source components, with the “human influence” component contributing 31% of the total PTR-MS measured VOC mixing ratio. Furthermore, indoor sulfur-containing compounds, including sulfuric acid and methanesulfonic acid (MSA), were observed for the first time. Correlation of sulfuric acid and MSA with CO2 indicates that their formation may be influenced by the presence of occupants via occupant-related surface reactions. This study suggests that human-related sources can contribute significantly to indoor VOCs and are a major sink for indoor O3, thereby substantially altering VOC composition, oxidative capacity, and possibly the potential for secondary organic aerosol formation in indoor air.

Contribution of human related sources to indoor volatile organic compounds

249th National Meeting (2015)

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