[A-AS11] Atmospheric Chemistry

[AAS11-19] Test measruemet of VOCs using SIFT-MS at suburban area

*Shungo Kato¹, Satoshi Inomata², Masaki Shikata³, Motonobu Iga³, Toshio Ii ³ (1.Tokyo Metropolitan University, 2.National Institute for Environmental Studies, 3.Kinryo Electric CO., LTD)

Keywords:volatile organic compound, selected ion flow tube mass spectrometer, Gas chromatography/Flame ionization detector

Volatile organic compounds (VOCs) play important roles in controlling air quality because they undergo gas-phase photochemical reactions leading to the formation of ozone and secondary organic aerosols. Since the atmospheric lifetimes of VOCs range from a few hours to several tens of days, high temporal-resolution measurements of reactive VOCs are required. On-line chemical ionization mass spectrometry (CI-MS) allows the real-time measurement of multiple VOCs. Such the technique is potentially advantageous compared to traditional gas chromatographic (GC) analyses because it does not require any sample treatment such as drying and/or preconcentration, and it is suitable for oxygenated VOCs, which are difficult to quantify from canister samples. Proton transfer reaction mass spectrometry (PTR-MS) is world-widely used for the real-time measurements of VOCs in air, but alkanes cannot be measured by PTR-MS. Selected ion flow tube mass spectrometry is a technique which utilizes known ion -molecule reactions of mass-selected reagent ions (typically H₃O⁺, NO⁺, and O₂⁺) with an analyte. Using NO⁺ as the reagent ion, alkanes can be measured. In this study, we demonstrated the real-time measurements of VOCs in air at suburban area by SIFT-MS and the SIFT-MS derived concentrations of hydrocarbons (HCs) were compared with those derived from gas chromatography/flame ionization detector (GC/FID). The measurements were carried out at the campus of Tokyo Metropolitan University in Hachioji, Tokyo, from 26 October to 4 November in 2021. Temporal variations of the mixing ratios for about 50 VOCs including HCs and oxygenated VOCs (OVOCs) and ammonia were measured at an interval of about 1 minute. Generally, good correlations between the SIFT-MS derived concentrations and the GC/FID-derived concentrations of HCs were obtained, but the slop was not 1 for some HCs. We found that SIFT-MS is a good tool for the real-time measurements of VOCs in ambient air, but some cautionary points were also found when we use it for the measurements of VOCs in ambient air.