Emission factors for light-duty vehicles equipped with three-way catalytic converter based on micro-reactor studies: a proposal for ammonia, nitrous oxide and molecular hydrogen

In this work, we report a methodology to provide emission factors based on micro-reactor studies. We propose emission factors for ammonia (NH3, 158 mg/km), nitrous oxide (N2O, 322 mg/km) and molecular hydrogen (H2, 72 mg/km) for vehicles equipped with three-way catalytic converter (TWC). Our experimental conditions were similar to those prevailing on vehicles during catalyst light-off and transient urban driving cycle. NH3 and H2 emission factors reported in this work are quantitatively similar to those reported from vehicles. However, for N2O our results are almost 6 times higher than the average reported from vehicles during catalyst light-off. It is possible that the emission factor of N2O from light-duty vehicles reported during catalyst light-off is underestimated because the time (8.4 min) for recollecting the N2O emission contained in the exhaust gases is largest than the time (4 min) required to produce the main emission of N2O on the three way catalyst. The methodology represents one of the first attempts to predict emission factors from a micro-reactor. Besides, our proposal has the advantage that the main parameters involved in the formation of NH3, N2O and H2 can be controlled. Our method also complements the experimental strategies to estimate emissions, which are difficult to observe during the measurements of these compounds on vehicles.