Ammonia (NH3) emissions from road traffic increasingly contribute to secondary aerosol formation in the urban atmosphere. Herein we report on the efficiency of the catalytic reduction of nitrogen monoxide and the catalyst selectivity towards ammonia at real world driving conditions. Intensive formation of ammonia was detected for a gasoline-fueled passenger car equipped with a Pd/Rh-based threeway- catalyst (TWC). Post-catalyst NH3 emission factors varied by two orders of magnitude from 1 to 120 mg/km and a strong dependence on velocity and acceleration was observed. Excellent nitrogen monoxide conversion above 98 % was found when ammonia formation was most intense. This complementary behavior indicates a dependence of the catalyst-induced NH3 formation on the air-to-fuel ratio with highest emissions at fuel-rich combustion and lowest emission rates at lean conditions. From time-resolved emission data we also concluded that transient driving has a major impact on the extent of ammonia formation and emission factors determined at steady state conditions may underestimate ammonia emissions at real world driving.
Three-way catalyst-induced formation of ammonia - velocity - and acceleration-dependent emission factors
2004
8 Seiten, 4 Bilder, 1 Tabelle, 3 Quellen
Conference paper
English