Abstract
Abstract. During the field campaign ZEPTER-2 in autumn 2008 whole air samples were collected on board a Zeppelin NT airship in the planetary boundary layer (PBL) and the lower free troposphere (LFT) over south-west Germany using the ZEppelin Based Isotope Sampler (ZEBIS). These samples were analysed with respect to volatile organic compound (VOC) mixing ratios and stable carbon isotope ratios using a gas chromatograph combustion isotope ratio mass spectrometer (GC-C-IRMS). In this study we present results for toluene, one of the major anthropogenic pollutants, which emphasise the viability of isotope ratio measurements in VOC for atmospheric research, especially to study VOC sources or to track both dynamical and chemical processes. In situ measurements of CO mixing ratios on board the Zeppelin NT were used to allocate the air samples either to the PBL or the LFT. In the PBL we observed rather fresh emissions mixing into the background air. We estimated a toluene source isotope ratio of δ13C = −28.2 ± 0.5‰. Samples from the PBL and the LFT were clearly distinguishable by means of their mixing ratio and isotope ratio signatures. Using the concept of the effective kinetic isotope effect, we were able to separate the effects of dilution processes and photochemical degradation in the free troposphere. We calculated the photochemical age of toluene in the atmosphere in two different ways using isotope ratios and mixing ratios. The results differ strongly in the PBL, probably due to mixing processes, but are compatible with each other in the LFT. Here, they correlate with a slope of 0.90±0.31.
Highlights
Despite their low concentrations volatile organic compounds (VOC) play an important role in atmospheric chemistry
The majority of anthropogenic VOC emissions stems from fossil fuel use and is emitted predominantly during road transport and oil production
Rudolph et al (1997) presented a method to determine stable carbon isotope ratios in VOC at ambient concentration levels using a gas chromatography combustion isotope ratio mass spectrometer (GC-C-IRMS). They proposed that measurements of the isotopic composition of VOC, beside measurements of their concentrations, would lead to valuable additional information on atmospheric processes
Summary
Despite their low concentrations volatile organic compounds (VOC) play an important role in atmospheric (especially tropospheric) chemistry. Rudolph et al (1997) presented a method to determine stable carbon isotope ratios in VOC at ambient concentration levels using a gas chromatography combustion isotope ratio mass spectrometer (GC-C-IRMS). They proposed that measurements of the isotopic composition of VOC, beside measurements of their concentrations, would lead to valuable additional information on atmospheric processes (e.g. photochemical degradation). This initial methodology has been followed by a number of studies on this subject (see e.g. the review of Goldstein and Shaw, 2003, and references therein)
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