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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/ m) of ∼ 1000, provides accurate m/z measurements ( m < 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 wellsuited 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.

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