Abstract
Formaldehyde (FM) and glyoxal (GL) are important atmospheric species of indoor and outdoor environments. They are either directly emitted in the atmosphere or they are formed through the oxidation of organic compounds by indoor and/or outdoor atmospheric oxidants. Despite their importance, the real-time monitoring of these compounds with soft ionization mass spectrometric techniques, e.g. proton transfer mass spectrometry (PTR-MS), remains problematic and is accompanied by low sensitivity. In this study, we evaluate the performance of a multi-ion selected ion flow tube mass spectrometer (SIFT-MS) to monitor in real-time atmospherically relevant concentrations of FM and GL under controlled experimental conditions. The SIFT-MS used is operated under standard conditions (SC), as proposed by the supplier, and customized conditions (CC), to achieve higher sensitivity. In the case of FM, SIFT-MS sensitivity is marginally impacted by RH, and the detection limits achieved are below 200 ppt. Contrariwise, in the case of GL, a sharp decrease of instrument sensitivity is observed with increasing RH when the H3O+ ion is used. Nevertheless, the detection of GL using NO+ precursor ion is moderately impacted by moisture with an actual positive sensitivity response. Therefore, we recommend the use of NO+ precursor for reliable detection and quantitation of GL. This work evidences that SIFT-MS can be considered as an efficient tool to monitor the concentration of FM and GL using SIFT-MS in laboratory experiments and potentially in indoor or outdoor environments. Furthermore, SIFT-MS technology still allows great possibilities for sensitivity improvement and high potential for monitoring low proton transfer affinity compounds.
Highlights
Formaldehyde (CH2O, FM) is the lightest aldehyde
Our strategy to operate the selected ion flow tube mass spectrometer (SIFT-MS) instrument under different modes, allowed us to shed light on the ion chemistry occurring in the flow tube and to identify the key reactions and processes that define the sensitivity of the instrument towards FM
Based on the detection limits achieved with the H3O+ ion, we suggest that SIFT-MS is not able to monitor GL in outdoor ambient air due to the strong impact of relative humidity (RH) on GL sensitivity, but it can be deployed efficiently in indoor environments and laboratory scale studies
Summary
Formaldehyde (CH2O, FM) is the lightest aldehyde. It is a ubiquitous chemical compound in outdoor and indoor environments. Formaldehyde is mainly formed by the oxidation of volatile organic compounds (VOCs), (Kefauver et al, 2014). FM plays an important role in atmospheric photochemistry since it is photolysed, producing hydroxyl (OH) and hydroperoxy (HO2) radicals which drive ozone (O3) production, (Atkinson, 2000). It enhances the formation of secondary organic aerosol (SOA) (Li et al, 2011). FM can be emitted directly from wood-based materials, construction materials, paintings, anthropogenic activities such as smoking, cooking, cleaning, or by the oxidation of indoor VOCs, especially terpenes, with high yields (Salthammer, 2019). Indoor concentrations of FM can reach significantly higher levels than outdoors (Crump et al, 1997; Langer et al, 2015; Liu et al, 2006)
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