Abstract
Abstract. We have developed a field-deployable gas chromatograph (GC) with thermal desorption preconcentration (TDPC), which is demonstrated here with automatic detector switching between two high-resolution time-of-flight mass spectrometers (TOF-MSs) for in situ measurements of volatile organic compounds (VOCs). This system provides many analytical advances, including acquisition of fast time–response data in tandem with molecular speciation and two types of mass spectral information for each resolved GC peak: molecular ion identification from Vocus proton transfer reaction (PTR) TOF-MS and fragmentation pattern from electron ionization (EI) TOF-MS detection. This system was deployed during the 2018 ATHLETIC campaign at the University of Colorado Dal Ward Athletic Center in Boulder, Colorado, where it was used to characterize VOC emissions in the indoor environment. The addition of the TDPC-GC increased the Vocus sensitivity by a factor of 50 due to preconcentration over a 6 min GC sample time versus direct air sampling with the Vocus, which was operated with a time resolution of 1 Hz. The GC-TOF methods demonstrated average limits of detection of 1.6 ppt across a range of monoterpenes and aromatics. Here, we describe the method to use the two-detector system to conclusively identify a range of VOCs including hydrocarbons, oxygenates, and halocarbons, along with detailed results including the quantification of anthropogenic monoterpenes, where limonene accounted for 47 %–80 % of the indoor monoterpene composition. We also report the detection of dimethylsilanediol (DMSD), an organosiloxane degradation product, which was observed with dynamic temporal behavior distinct from volatile organosiloxanes (e.g., decamethylcyclopentasiloxane, D5 siloxane). Our results suggest DMSD is produced from humidity-dependent heterogeneous reactions occurring on surfaces in the indoor environment, rather than formed through gas-phase oxidation of volatile siloxanes.
Highlights
Volatile organic compound (VOC) emissions from transportation were the most important air pollution source in urban environments (Gentner et al, 2017; Watson et al, 2001)
To address the need for high time resolution measurements and molecular identification of volatile organic compounds (VOCs), we have developed an automated, fielddeployable gas chromatograph (GC) equipped with thermal desorption (TD) preconcentration and automated detector switching between two high-resolution time-of-flight mass spectrometers (HR-TOFMS): a Vocus proton transfer reaction (PTR)-TOF-mass spectrometry (MS) and an electron ionization (EI) TOF-MS for in situ measurements of VOCs
In this study we present a field-deployable in situ GC with thermal desorption preconcentration and automatic switching between two time-of-flight mass spectrometric detectors, Vocus PTR-TOF-MS and EI-TOF-MS
Summary
Volatile organic compound (VOC) emissions from transportation were the most important air pollution source in urban environments (Gentner et al, 2017; Watson et al, 2001). VCPs consist of a large diversity of compounds, including oxygenated species like alcohols (e.g., glycols), esters, siloxanes, and carbonyls, along with hydrocarbons like alkanes, alkenes (e.g., monoterpenes), and aromatics (McDonald et al, 2018). This emission class stems from human activities. To understand changing emission patterns, analytical instrumentation that can quantitatively detect these classes of VOCs with little ambiguity and high time resolution is needed, along with a range of studies to understand how emissions differ depending on the indoor environment and its use
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