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.