Sulfide Emissions from Catalyst-Equipped Cars

An on-stream gas chromatographic technique was developed to analyze grab samples of diluted and undiluted vehicle exhaust for the reduced sulfur compounds which cause rotten-egg odors. This method was used to conduct a brief survey of two cars with modified carburetors, four customer cars with odor problems, and five experimental three-way catalyst cars. The cars were tested on a chassis dynamometer using a driving cycle developed for this study. Hydrogen sulfide and carbonyl sulfide were frequently measured. Ethyl mercaptan and fuel sulfur components were occasionally detected. The sulfides were emitted most often when the catalyst was hot, the space velocity was low and the carburetion was rich. The maximum H₂S or COS concentration measured in undiluted exhaust was <10 ppm. Therefore, these emissions pose no known health problem, but can be an odor problem.