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EPA published the first results from evaluations of electrically heated catalyst (EHC) technology for light-duty automotive applications. Since then, a number of automakers, suppliers, and government agencies have published results from their heated catalyst development and evaluation programs. EPA has evaluated a number of start catalyst systems incorporating an EHC start catalyst followed by a larger, conventional main catalyst. These systems have proven very effective at reducing cold start related emissions from methanol vehicles at low mileage. This paper compares the results from several EHC + main catalyst evaluations conducted by EPA.

Studies of emissions from vehicles equipped with catalysts have shown that some unregulated emissions can increase when a catalyst is used. One example of this is sulfuric acid, which has been studied extensively. Other unregulated emissions include ammonia and hydrogen cyanide. In a number of studies, these unregulated pollutant emissions have been measured from light-duty vehicles and heavy-duty engines. These emission levels were used in air quality dispersion models to predict the resultant air quality levels. The ambient concentrations predicted for each pollutant were then compared to suggested concentrations at which adverse health effects may be found to determine if additional monitoring or control would be indicated for these pollutants. It was determined that mobile source emissions of sulfuric acid, hydrogen cyanide, and ammonia do not in general result in ambient levels of concern for the air quality situations studied.