A technique for compound-specific analysis of stable carbonisotope ratios and concentration of ambient volatile organic compounds (VOCs)is presented. It is based on selective VOC sampling onto adsorbent-filledcartridges by passing large volumes of air (up to 80 L) through thecartridge. The hydrocarbons are recovered by thermal desorption followed bytwo-step cryogenic trapping and then are separated by gas chromatography inthe laboratory. Once separated, individual VOCs are subjected to onlineoxidation in a combustion interface and isotope ratio analysis by isotoperatio mass spectrometry. The method allows measurements of stable carbonisotope ratios of ambient aromatic VOCs present in low pptV to ppbV levelswith an accuracy of typically better than 0.5 ‰. Theprecision of concentration measurements is better than 10%. Examples ofmeasurements conducted as part of a joint Environment Canada–York University(EC-YU) measurement campaign at a semi-rural location demonstrate that theability to make accurate measurements in air with low VOC mixing ratios isimportant to avoid bias from an overrepresentation of samples that arestrongly impacted by recent emissions.
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