Trends of NO-, NO2-, and NH3-emissions from gasoline-fueled euro-3-to euro-4-passenger cars

Vehicular emissions of reactive nitrogen compounds (RNCs) such as nitric oxide (NO), nitrogen dioxide (NO,), and ammonia (NH3) have a substantial impact on urban air quality. NO and NO2 support the photochemical formation of ozone, and NH3 is involved in the atmospheric formation of secondary aerosols. Vehicular NO is mainly formed during combustion, whereas NO, and NH3 are both secondary pollutants of the catalytic converter systems. Herein we report on tail-pipe RNC emissions of gasoline-fueled Euro-3- and Euro-4-passenger cars at transient driving from 0 to 150 km h(-1). Two sets of 10 in-use vehicles with comparable engine size and mileage were studied with time-resolved chemical ionization-mass spectrometry (CI-MS). Each vehicle was tested in 7 different driving cycles including the legislative European (EDC) and the US FTP-75 driving cycles. Mean emission factors (EFs) for different traffic situations are reported and effects of cold start, velocity, acceleration, and deceleration are discussed. Furthermore, critical operating conditions supporting the de novo formation of NH3 have been identified. In the EDC, mean NO- and NH3-EFs of 57 +/- 26 and 16 +/- 12 mg km(-1) were obtained for Euro-3-vehicles; those of the Euro-4-technology were lower by about 25% and 33% at the levels of 43 +/- 46 and 10 +/- 7 mg km(-1), respectively. NO2 emissions of the investigated three-way catalyst (TWC) vehicles accounted for < 1% of the detected RNCs, whereas NH3 was found to be the dominant RNC for most vehicle conditions. Molar NH3 proportions varied from about 0.4-0.8, as soon its catalyst fight-off occurred. NO was found in large excess only during the cold-start period. Catalyst fight-off is indicated by a fast transition from NO- to NH3-rich exhaust. Velocity and acceleration had pronounced effects on the RNC emission characteristics. Mean velocity-dependent EFs for NO and NH3 varied by about one order of magnitude from 10 to 74 and 15 to 161 mg km(-1) for Euro-3-vehicles and from 12 to 44 and 7 to 144 mg km(-1) for the Euro-4 fleet. We conclude that the investigated Euro-3- and Euro-4-vehicles are mainly operated under slightly reducing conditions, where the NH3 emissions dominate over those of the NO. Under these conditions, both vehicle fleets on in average fulfilled the valid Euro-3 and Euro-4 limits for nitrogen oxides (NOx) of 150 and 80 mg km(-1), respectively (as NO2 equivalents). (c) 2007 Elsevier Ltd. All rights reserved.