Modern mass spectrometry in atmospheric sciences: Measurement of volatile organic compounds in the troposphere using proton‐transfer‐reaction mass spectrometry

Abstract

Volatile organic compounds (VOCs) in the troposphere are emitted from a wide variety of natural and man‐made sources and resulting in environmental issues such as air pollution and climate change. Proton‐transfer‐reaction mass spectrometry (PTR‐MS), a chemical ionization mass spectrometry technique using H3O+ reagent ions, allows real‐time measurements of various VOCs in air with high sensitivity (parts‐per‐trillion to parts‐per‐billion level) and fast time response (<1 s). Modern PTR‐MS equipped with time‐of‐flight mass analyzers can measure hundreds of compounds simultaneously. The applications of PTR‐MS have greatly promoted understanding VOC sources and their roles in environmental issues, and therefore, PTR‐MS has become a well‐established analytical technique for in situ VOC measurements in atmospheric sciences. Here, the principles and implementation of PTR‐MS are described. We additionally highlight modern PTR‐MS techniques for accurate identification and comprehensive quantification of various VOCs. Finally, recent applications for atmospheric science are presented, using examples from research in biomass burning emissions and chemistry.

VOC emissions by fresh and old asphalt pavements at service temperatures: impacts on urban air quality

“…When a STA or LTA asphalt mixture was inserted in the atmospheric chamber, concentrations were measured with the PTR-ToFMS, and then converted into EFs using eqn (2). Peaks observed on mass spectra at M + 1 were tentatively assigned using molecular formulae of VOCs (of molar mass M ) observed by other groups; 35,40–43 a comprehensive assignment of PTR-ToFMS masses can be found in Yañez-Serrano et al 44 102 masses have thus been followed (see Table S3 in ESI†), from mass 15 to 225. VOC emission factors were calculated based on 78 masses, after inorganic ions, reagent ions, fragments ( M + 1 < 40 Da), and M + 1 > 200 Da have been excluded (lines shaded in orange in Table S3†).…”

Evaluation of the VOC pollution pattern and emission characteristics during the Beijing resurgence of COVID-19 in summer 2020 based on the measurement of PTR-ToF-MS

“…Besides, a large part of OVOCs derives from secondary formation, which exerts an important impact on the atmospheric photochemical cycle (Huang et al 2020). The sensitivity of PTR-MS is related to the protontransfer reaction rate constant, hence it is more suitable for the measurement of OVOCs that cannot be calibrated directly (Sekimoto and Koss 2021). The most abundant OVOC species detected in this study was acetone + propanal (4.07 ± 1.15 ppbv), followed by methanol (3.49 ± 1.66 ppbv) and acetaldehyde (3.42 ± 1.21 ppbv).…”

A Method for High Throughput Free Fatty Acids Determination in a Small Section of Bovine Liver Tissue Using Supercritical Fluid Extraction Combined with Supercritical Fluid Chromatography-Medium Vacuum Chemical Ionization Mass Spectrometry

“…1) However, PTR-MS uses a pure H 3 O + as a reagent ion to simultaneously determine amounts of volatile organic compounds in gaseous samples, which are determined using reaction kinetics. 2) In contrast, MVCI uses both H 3 O + and OH − as reagent ions to determine amounts of both volatile and non-volatile organic compounds so that it is capable of monitoring both positive and negative ions from a single sample submission if the mass analyzer is capable of it. The MVCI exhibits excellent advantages for monitoring the lipophilic molecules extracted by supercritical fluid extraction (SFE) 3) such as 1) extremely high sensitivity, 2) excellent compatibility with the supercritical carbon dioxide (scCO 2 ), and 3) ease of adopting existing mass spectrometers using liquid chromatography as an inlet.…”