Monoterpenes and monoterpenoids are commonly found in volatile chemical products (VCPs) used in residential buildings. Real-time measurements via proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) can capture rapid changes in the chemical composition of indoor air during the use of VCPs. However, PTR-TOF-MS cannot separate monoterpene and monoterpenoid isomers, which are highly reactive with ozone (O<sub>3</sub>) and the hydroxyl radical (OH) and can initiate indoor secondary organic aerosol formation. The variable reactivity of monoterpene and monoterpenoid isomers with O<sub>3</sub> and OH can impact indoor air chemistry. Thus, isomer-resolved measurements of VCP emissions in buildings are needed to elucidate how the use of VCPs modulate indoor air composition and chemical exposures among occupants. Coupling gas chromatography with PTR-TOF-MS enables for isomer separation, while achieving high time-resolution indoor measurements of monoterpene and monoterpenoid emissions. Fast gas chromatography (fastGC)-PTR-TOF-MS measurements were conducted at the Purdue zero Energy Design Guidance for Engineers (zEDGE) Tiny House to separate and identify monoterpene and monoterpenoid isomers emitted from VCPs, including personal care products, cleaning agents, candles, and wax warmers. First, to build a database of retention times and fragmentation patterns for monoterpenes and monoterpenoids, online headspace sampling was conducted for twenty diluted monoterpene and monoterpenoid liquid standards, including α-pinene, β-pinene, limonene, and linalool. The database was then used to determine the terpene composition of VCP emissions via both headspace sampling and full-scale experiments of real-life indoor activities in the Purdue zEDGE Tiny House.  Preliminary results of fastGC-PTR-TOF-MS measurements reveal that many household VCPs contain complex mixtures of monoterpenes and monoterpenoids. More than five different monoterpenes or monoterpenoids were detected in the indoor emissions from most VCPs. Results of this study will help improve our understanding of how VCPs affect indoor air chemistry, chemical exposures in buildings, and indoor-to-outdoor emissions of reactive terpene mixtures.

Online monitoring of terpene isomer emissions from volatile chemical products in buildings via fast gas chromatography-proton transfer reaction mass spectrometry

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