Many problems have been reported with the method and instruments presently used to monitor ambient air hydrocarbons. The study reported here was carried out to determine, if possible, the sources of error inherent with the present technique and to make recommendations as to what modifications can be made to eliminate or minimize these errors. A flame ionization detector and gas chromatographic instrument were designed, built and evaluated to determine the effects of operating parameters on hydrocarbon response and the differences in response to various non-methane hydrocarbon (NMHC) species. This instrument was then used in a comparative evaluation with six commercial instruments. The evaluation included determinations of calibration stability and response to various NMHC species. Following measurements with gases from cylinders from commercial sources, the commercial instruments were further compared in a three day test using ambient air. Calibration stability was found to be reasonable, with span shifts of greater than 5% the biggest problem. There were wide differences in responses to different NMHC species. These differences were somewhat reduced by using propane responses as the basis of calibration rather than methane. When ambient air was analyzed there were large discrepancies between analyzer readings which appeared to be related to atmospheric water vapor content. Recommendations are made for changes in technique to minimize analyzer discrepancies.

Project Officer: E. Carol Ellis. Prepared for the United States Environmental Protection Agency by Research Triangle Institute. Contract Number: 68-02-1800 "June 1977." Includes bibliographical references. "EPA-600/4-77-033."