Automotive Hydrocarbon Emission Patterns in the Measurement of Nonmethane Hydrocarbon Emission Rates

The advent of emission control technology has resulted in significant changes in both the total mass and detailed patterns of hydrocarbons emitted from automobiles. Emission rates of 56 hydrocarbons from 22 motor vehicles, including catalyst and noncatalyst configurations, were determined for the Federal Urban Driving Cycle.

An increased relative abundance of methane is indicated for vehicles equipped with oxidation catalysts. In view of the photochemically non-reactive nature of methane, simple and economic procedures for determination of vehicle nonmethane hydrocarbon emission rates are evaluated. In general the procedures evaluated require independent total hydrocarbon and methane analysis, with the nonmethane hydrocarbon level calculated by difference.

The procedures are evaluated by comparison of indicated nonmethane hydrocarbon emission rates with rates obtained by summation of individual compound rates determined by advanced gas chromatographic procedures.