Calibration and intercomparison of acetic acid measurements using proton-transfer-reaction mass spectrometry (PTR-MS)

[摘要] Acetic acid is one of the most abundant organic acids in the ambientatmosphere, with maximum mixing ratios reaching into the tens of parts perbillion by volume (ppbv) range. The identities and associated magnitudes ofthe major sources and sinks for acetic acid are poorly characterized, due inpart to the limitations of available measurement techniques. This paperdemonstrates that, when properly calibrated, proton-transfer-reaction massspectrometry (PTR-MS) can be a valuable technique for fast response,accurate quantification of acetic acid in ambient air. Three differentPTR-MS configurations were calibrated at low ppbv mixing ratios usingpermeation tubes, which yielded calibration factors between 7.0 and 10.9normalized counts per second per ppbv (ncps ppbv⁻¹) at adrift tube field strength of 132 Townsend (Td). Detection limits ranged from0.06 to 0.32 ppbv with dwell times of 5 s. These calibration factorsshowed negligible humidity dependence. Acetic acid was measured with PTR-MSon Appledore B Island, ME, during the International Consortium for AtmosphericResearch on Transport and Transformation (ICARTT) campaign and validatedbased on acetic acid measured in parallel using tandem mist chambers coupledwith ion chromatography (MC/IC). Mixing ratios ranged from a minimum of0.075 ± 0.004 ppbv to 3.555 ± 0.171 ppbv, with a median mixingratio of 0.530 ± 0.025 ppbv. An orthogonal least squares linearregression of paired data yielded a slope of 1.14 ± 0.06 (2σ),an intercept of 0.049 ± 0.020 (2σ) ppbv, and an R² of0.78.

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