Ammonia Emissions from the EPA's Light Duty Test Vehicle

Ammonia (NH₃) emissions were measured from the EPA's Light Duty Test Vehicle while operated on a chassis dynamometer. The vehicle's (1993 Chevrolet equipped with a three-way catalyst) emissions were measured for three transient (urban driving, highway fuel economy, and hard acceleration) cycles and steady state operation. Previous research^{1, 2} has shown that NH₃ is predominately emitted from vehicles with a catalyst (three-way or dual-bed). The vehicle's catalyst is designed to reduce nitrogen oxides (NO_x) to nitrogen (N₂) and oxygen (O₂) during normal operation. The reduction of NO_x to NH₃ occurs during periods of reducing conditions when insufficient O₂ is available. NH₃ emissions were measured during fuel-rich/reduced-O₂ conditions (open-loop control scheme). The results demonstrate that NH₃ production is correlated to combustion conditions³. The results also show that the amount of NH₃ produced correlates with the amount of time that the vehicle remains in the open-loop control scheme. The significance of this finding is that NH₃ production can be predicted for a fleet based on the frequency of enrichment of vehicles equipped with a three-way catalyst. The results also provide a means of determining the location of roadway links and/or specific locations where NH₃ production can be anticipated based on predicted engine power.