Chassis Dynamometer Testing of Ammonia Emissions from Light-Duty SI Vehicles in the Context of Emissions of Reactive Nitrogen Compounds

Ammonia is a reactive nitrogen compound (RNC - nitrogen-based gaseous molecules with multiple adverse impacts on human health and the biosphere). A three-way catalyst can produce substantial quantities of ammonia through various reaction pathways. This study presents a brief literature review, and presents experimental data on ammonia emissions from seven Euro 5 passenger cars, using different gasoline fuels and a CNG fuel. All vehicles were tested on a chassis dynamometer over the New European Driving Cycle. For six of the vehicles, ammonia was quantified directly at tailpipe (using two different analyzers); emissions from one vehicle were subjected to Fourier Transform Infra-Red (FTIR) analysis. Emissions of ammonia from these vehicles were generally low in comparison to other chassis dynamometer studies, perhaps attributable to the favorable laboratory test conditions and the age of the vehicles. Transient data revealed small but significant differences in ammonia emissions, including the time of the initial ammonia surge, depending on the test fuel and the fuel injection strategy. A range of metrics were examined to determine possible correlations between ammonia and other pollutants. No significant correlations were found; there was, however some evidence of a trade-off relationship between ammonia and NO_x. An analysis of ammonia emissions in the context of RNC emissions revealed ammonia to make up roughly 18% of the RNCs released over the duration of the test cycle. Thus, the ammonia emissions observed here were low, but non-trivial, and the issue of automotive ammonia emissions and impacts on air quality is an important research direction.