Articles | Volume 10, issue 1
Atmos. Meas. Tech., 10, 281–289, 2017
Atmos. Meas. Tech., 10, 281–289, 2017

Research article 26 Jan 2017

Research article | 26 Jan 2017

Using in situ GC-MS for analysis of C2–C7 volatile organic acids in ambient air of a boreal forest site

Heidi Hellén1, Simon Schallhart2, Arnaud P. Praplan1, Tuukka Petäjä2, and Hannele Hakola1 Heidi Hellén et al.
  • 1Finnish Meteorological Institute, P.O. Box 503, 0011 Helsinki, Finland
  • 2Department of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland

Abstract. An in situ method for studying gas-phase C2–C7 monocarboxylic volatile organic acids (VOAs) in ambient air was developed and evaluated. Samples were collected directly into the cold trap of the thermal desorption unit (TD) and analysed in situ using a gas chromatograph (GC) coupled to a mass spectrometer (MS). A polyethylene glycol column was used for separating the acids. The method was validated in the laboratory and tested on the ambient air of a boreal forest in June 2015. Recoveries of VOAs from fluorinated ethylene propylene (FEP) and heated stainless steel inlets ranged from 83 to 123 %. Different VOAs were fully desorbed from the cold trap and well separated in the chromatograms. Detection limits varied between 1 and 130 pptv and total uncertainty of the method at mean ambient mixing ratios was between 16 and 76 %. All straight chain VOAs except heptanoic acid in the ambient air measurements were found with mixing ratios above the detection limits. The highest mixing ratios were found for acetic acid and the highest relative variations for hexanoic acid. In addition, mixing ratios of acetic and propanoic acids measured by the novel GC-MS method were compared with proton-mass-transfer time-of-flight mass spectrometer (PTR-TOFMS) data. Both instruments showed similar variations, but differences in the mixing ratio levels were significant.

Short summary
There is a lack of knowledge of volatile organic acids (VOAs), other than formic and acetic acids in gas phase, and this is at least partly due to the lack of sensitive enough measurement methods. In the present study we developed an in situ GC–MS measurement method for measuring C2–C7 monocarboxylic VOAs at ambient air concentration levels, which we used to measure ambient air concentrations in a boreal forest site. In addition, found mixing ratios were compared with PTR-TOFMS data.