Abstract
Abstract. Herein, we report on the development of a compact proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) for airborne measurements of volatile organic compounds (VOCs). The new instrument resolves isobaric ions with a mass resolving power (m/Δm) of ~1000, provides accurate m/z measurements (Δm < 3 mDa), records full mass spectra at 1 Hz and thus overcomes some of the major analytical deficiencies of quadrupole-MS-based airborne instruments. 1 Hz detection limits for biogenic VOCs (isoprene, α total monoterpenes), aromatic VOCs (benzene, toluene, xylenes) and ketones (acetone, methyl ethyl ketone) range from 0.05 to 0.12 ppbV, making the instrument well-suited for fast measurements of abundant VOCs in the continental boundary layer. The instrument detects and quantifies VOCs in locally confined plumes (< 1 km), which improves our capability of characterizing emission sources and atmospheric processing within plumes. A deployment during the NASA 2013 DISCOVER-AQ mission generated high vertical- and horizontal-resolution in situ data of VOCs and ammonia for the validation of satellite retrievals and chemistry transport models.
Highlights
Volatile organic compounds (VOCs) are ubiquitous in the Earth’s troposphere, and many of them are intimately involved in HOx-NOx-O3 chemistry and in secondary organic aerosol formation
We show that the newly developed instrument is capable of generating full mass scan information at 1 Hz and of resolving a series of isobaric interferences known from conventional PTR-quadrupole mass spectrometer (QMS) studies
Instrument sensitivities range from 60.4 cps ppbV−1 for methanol to 148.9 cps ppbV−1 for 1,3,5-trimethylbenzene. 2σ detection limits for 1 Hz data are between 0.05 ppbV for 1,3,5-trimethylbenzene and 0.45 ppbV for methanol
Summary
Volatile organic compounds (VOCs) are ubiquitous in the Earth’s troposphere, and many of them are intimately involved in HOx-NOx-O3 chemistry and in secondary organic aerosol formation. A number of groups have used orthogonal acceleration time-of-flight mass spectrometers (oa-TOF-MS) in combination with a glow-discharge drift tube ion source (Blake et al, 2004; Ennis et al, 2005; Tanimoto et al, 2007; Jordan et al, 2009; Graus et al, 2010) None of those instruments has yet been deployed on an atmospheric chemistry research aircraft which is a challenging measurement platform (short power-up time, shocks and vibrations during takeoff and landing, variable pressure and temperature in the cabin, contamination with polluted air at the airport, etc.). Examples of field data are presented to demonstrate the analytical power of the new airborne PTR-ToF-MS instrument in characterizing point emissions of VOCs and in measuring vertical trace gas profiles at high spatial resolution.
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