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The new California LEV-II regulations for “near zero” evaporative emissions require a 75% reduction from current emission levels for light duty vehicles. To meet the challenge of satisfying these new regulations, there is an immediate need for an increased understanding of the sources of evaporative emissions. Hydrocarbon speciation by gas chromatography is a powerful analytical tool for determining the composition of complex hydrocarbon mixtures. Gas chromatography and gas chromatography/mass spectrometry were used to identify the volatile organic compounds (VOC) present in the evaporative emissions from a number of prototype and recent production model gasoline-fueled vehicles. For a “typical” evaporative emissions sample, more than 90% of the emissions were found to be fuel-type hydrocarbons.

Although the intent of the SHED test (Sealed Housing for Evaporative Determination) is to measure evaporative fuel losses, the SHED sampling methodology in fact measures hydrocarbons from all vehicle and test equipment sources. Leakage of air conditioning (AC) refrigerant is one possible non-fuel source contributing to the SHED hydrocarbon measurement. This report describes a quick and relatively simple method to identify the contribution of AC refrigerant to the SHED analyzer reading. R134A (CH2FCF3), the hydrofluorocarbon refrigerant used in all current automotive AC systems, as well as its predecessor, the chlorofluorocarbon R12, can be detected using the gas chromatography methods currently in place at many emissions labs for the speciation of exhaust and evaporative hydrocarbon emissions.