07 Nov 2022
07 Nov 2022
Status: this preprint is currently under review for the journal AMT.

Influence of ozone and humidity on PTR-MS and GC-MS VOC measurements with and without Na2S2O3 ozone scrubber

Lisa Ernle, Monika Akima Ringsdorf, and Jonathan Williams Lisa Ernle et al.
  • Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

Abstract. The measurement of volatile organic compounds (VOCs) can be influenced by ozone (O3), resulting in sampling artifacts that corrupt the data obtained. Published literature reports both, positive (false enhancements of signal) and negative (loss of signal) artifacts in VOC data due to ozonolysis occurring in the sample gas. To assure good data quality it is essential to be aware of such artifact inducing processes, characterize them and try to minimize the impact with a suitable sampling setup. Here we present results from experiments with a sodium thiosulfate ozone scrubber (Na2S2O3), which is a cost effective and easily applied option for O3 scavenging during gas phase sampling. Simultaneous measurement of selected organic trace gases using gas chromatography- and proton transfer reaction-mass spectrometry was performed at different ozone levels (0–1 ppm) and different relative humidities (0–80 %). In this way both tropospheric and stratospheric conditions were examined. The measured data show that several carbonyl compounds including acetaldehyde, acetone and propanal show artificial signal enhancement when ozone is present at higher concentrations (>150 ppb) in dry air, while analytes with double bonds like isoprene (measured with GC-MS) and terpenes show lower signals due to reaction with ozone. Both effects can be eliminated or in the case of sesquiterpenes substantially reduced by using Na2S2O3 impregnated quartz filters in the inlet line. With the chosen scrubbing material, relative humidity (RH) substantially improves the scrubbing efficiency. Under surface conditions between 50–80 % RH, the filter allows accurate measurement of all species examined.

Lisa Ernle et al.

Status: open (until 20 Dec 2022)

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Lisa Ernle et al.

Data sets

VOCdata_O3_Na2S2O3scrubber Ernle, Ringsdorf

Lisa Ernle et al.


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Short summary
Atmospheric ozone can induce artifacts in volatile organic compound measurements. Laboratory tests were made using GC-MS and PTR-MS aircraft systems under tropospheric and stratospheric conditions of humidity and ozone, with and without sodium thiosulfate filter scrubbers. Ozone in dry air produces some carbonyls and degrades alkenes. The scrubber lifetime depends on ozone concentration, flow rate and humidity. For the troposphere with scrubber, no significant artifacts were found over 14 days.