1995-02-01

CRC Speciated Hydrocarbon Emissions Analysis Round Robin Test Program 950780

Recent changes in regulatory practices have brought about a need for speciated analysis of the volatile organic components of vehicle exhaust. The purpose of this study was to allow interested laboratories to participate in a Round Robin so that each could assess its speciation methodologies for hydrocarbons, alcohols, and carbonyls. The results from analysis of the liquid samples (methanol, ethanol, and DNPH-derivatives of carbonyls) were reported in SAE 941944. For gaseous hydrocarbon samples, two gasolines from the Auto/Oil Air Quality Improvement Research Program (AQIRP) were used to prepare compressed gas cylinders of “synthetic exhaust.” These samples were also doped with typical light hydrocarbon combustion components, marker compounds, and MTBE (in one of the two sets of samples). The cylinders were circulated to 16 laboratories, which included automotive and petroleum companies, contract laboratories, and regulatory agencies.
Direct comparison of individual species' concentrations showed that interlaboratory variability was on the order of 10-15% (coefficient of variation) for most species present at >1 ppmC. For lower concentration species, higher relative variabilities were observed. Interlaboratory variability for total NMHC was 18-20%. Compositional profiles of the cylinder samples were generated by lumping the individual species results from each lab according to carbon number and hydrocarbon group type. These profiles were then compared with the mean profiles from all labs to identify areas of discrepancy. This comparative information is useful to participants wanting to improve their speciation capabilities.

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