Ammonia Emission Measurements for Light-Duty Gasoline Vehicles in China and Implications for Emission Modeling

Motor vehicle ammonia (NH3) emissions have attracted increasing attention for their potential to form secondary aerosols in urban atmospheres. However, vehicle NH3 emission factors (EFs) remain largely unknown due to a lack of measurements. Thus, we conducted detailed measurements of NH3 emissions from 18 Euro 2 to Euro 5 light-duty gasoline vehicles (LDGVs) in Shanghai, China. The distance- and fuel-based NH3 EFs average 29.2 ± 24.1 mg·km-1 and 0.49 ± 0.41 g·kg-1, respectively. The average NH3-to-CO2 ratio is 0.41 ± 0.34 ppbv·ppmv-1. The measurements reveal that NH3 emissions from LDGVs are strongly correlated with both vehicle specific power (VSP) and the modified combustion efficiency (MCE); these relationships were used to predict LDGV NH3 EFs via a newly developed model. The predicted LDGV NH3 EFs under urban and highway driving cycles are 23.3 mg·km-1 and 84.5 mg·km-1, respectively, which are consistent with field measurements. The NH3 EF has decreased by 32% in average since the implementation of vehicle emission control policies in China five years ago. The model presented herein more accurately predicts LDGV NH3 emissions, contributing substantially to the compilation of NH3 emission inventories and prediction of future motor vehicle emissions in China.