Hydrocarbon measurement discrepancies among various analyzers using flame-ionization detectors

Several experimenters have observed substantially discrepant nonmethane hydrocarbon measurements from various types of hydrocarbon analyzers measuring identical samples of ambient air. A number of flame-ionization analyzers was observed under controlled conditions while making simultaneous measurements of urban ambient air. Substantial discrepancies were found to occur among different models of analyzers. The standard deviations of these discrepancies averaged 0.322 part per million, which is extremely large with respect to the ambient air quality standard (guide) for nonmethane hydrocarbons, 0.24 part per million.