Stable carbon isotope ratios of toluene in the boundary layer and the lower free troposphere

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 δ 13 C = −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.

A method for stable carbon isotope ratio and concentration measurements of ambient aromatic hydrocarbons

“…The reproducibility of isotope ratio measurements for our newly developed method is better than 0.5 ‰, similar to that of other state-of-the-art methods for measurement of δ 13 C in ambient VOCs Eckstaedt et al, 2012;Kawashima and Murakami, 2014;Rudolph et al, 1997;Saito et al, 2009;Turner et al, 2006;Wintel et al, 2013); however, the lower limit of concentrations for which this precision can be achieved is significantly lower than that achieved by these other methods.…”

“…Many of the currently reported stable carbon isotope ratio data for ambient VOCs were obtained using whole air sampling in stainless steel canisters, which is adequate when measuring VOCs at ppbV and high pptV mixing ratios such as for source studies or polluted areas Redeker et al, 2007;Rudolph et al, 1997Saito et al, 2002). However, collecting whole air samples with the large volumes required for measurement of isotope ratios for VOC mixing ratios well below 1 ppbV is technically challenging (Wintel et al, 2013).…”

“…Cryogenic sampling has been used to collect VOCs from very large volumes of air (Bill et al, 2004Iannone et al, 2007Zuiderweg et al, 2011), but the technical and logistical challenges for field sampling are substantial. Selective sampling on adsorbent cartridges is a widely used inexpensive method for measurement of VOC concentrations and has recently been applied to collect VOC samples for isotope ratio analysis (Eckstaedt et al, 2011(Eckstaedt et al, , 2012.…”

Singular vector-based targeted observations of chemical constituents: description and first application of the EURAD-IM-SVA v1.0

“…We apply the set-up of the ZEPTER-2 measurement campaign (Zeppelin based tropospheric chemistry experiment, Part 2, Oebel et al, 2010;Wintel et al, 2013) to test and validate the EURAD-IM-SVA v1.0.…”

“…3. In order to test and validate EURAD-IM-SVA v1.0, we focus on the model set-up of the ZEPTER-2 campaign (Zeppelin based tropospheric chemistry experiment, Part 2, Oebel et al, 2010;Wintel et al, 2013). The ZEPTER-2 campaign study configurations are described in Sect.…”