3 research outputs found
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An in situ gas chromatograph with automatic detector switching between PTR- and EI-TOF-MS: isomer-resolved measurements of indoor air
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.
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Identification and Quantification of 4‑Nitrocatechol Formed from OH and NO<sub>3</sub> Radical-Initiated Reactions of Catechol in Air in the Presence of NO<sub><i>x</i></sub>: Implications for Secondary Organic Aerosol Formation from Biomass Burning
Catechol (1,2-benzenediol) is emitted from biomass burning and
produced from a reaction of phenol with OH radicals. It has been suggested
as an important secondary organic aerosol (SOA) precursor, but the
mechanisms of gas-phase oxidation and SOA formation have not been
investigated in detail. In this study, catechol was reacted with OH
and NO<sub>3</sub> radicals in the presence of NO<sub><i>x</i></sub> in an environmental chamber to simulate daytime and nighttime
chemistry. These reactions produced SOA with exceptionally high mass
yields of 1.34 ± 0.20 and 1.50 ± 0.20, respectively, reflecting
the low volatility and high density of reaction products. The dominant
SOA product, 4-nitrocatechol, for which an authentic standard is available,
was identified through thermal desorption particle beam mass spectrometry
and Fourier transform infrared spectroscopy and was quantified in
filter samples by liquid chromatography using UV detection. Molar
yields of 4-nitrocatechol were 0.30 ± 0.03 and 0.91 ± 0.06
for reactions with OH and NO<sub>3</sub> radicals, and thermal desorption
measurements of volatility indicate that it is semivolatile at typical
atmospheric aerosol loadings, consistent with field studies that have
observed it in aerosol particles. Formation of 4-nitrocatechol is
initiated by abstraction of a phenolic H atom by an OH or NO<sub>3</sub> radical to form a β-hydroxyphenoxy/<i>o</i>-semiquinone
radical, which then reacts with NO<sub>2</sub> to form the final product
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Overview of ICARUSA Curated, Open Access, Online Repository for Atmospheric Simulation Chamber Data
Atmospheric simulation chambers continue to be indispensable tools for research in the atmospheric sciences. Insights from chamber studies are integrated into atmospheric chemical transport models, which are used for science-informed policy decisions. However, a centralized data management and access infrastructure for their scientific products had not been available in the United States and many parts of the world. ICARUS (Integrated Chamber Atmospheric data Repository for Unified Science) is an open access, searchable, web-based infrastructure for storing, sharing, discovering, and utilizing atmospheric chamber data [https://icarus.ucdavis.edu]. ICARUS has two parts: a data intake portal and a search and discovery portal. Data in ICARUS are curated, uniform, interactive, indexed on popular search engines, mirrored by other repositories, version-tracked, vocabulary-controlled, and citable. ICARUS hosts both legacy data and new data in compliance with open access data mandates. Targeted data discovery is available based on key experimental parameters, including organic reactants and mixtures that are managed using the PubChem chemical database, oxidant information, nitrogen oxide (NOx) content, alkylperoxy radical (RO2) fate, seed particle information, environmental conditions, and reaction categories. A discipline-specific repository such as ICARUS with high amounts of metadata works to support the evaluation and revision of atmospheric model mechanisms, intercomparison of data and models, and the development of new model frameworks that can have more predictive power in the current and future atmosphere. The open accessibility and interactive nature of ICARUS data may also be useful for teaching, data mining, and training machine learning models