Effects of Ammonia Mitigation on Secondary Organic Aerosol and Ammonium Nitrate Particle Formation in Photochemical Reacted Gasoline Vehicle Exhausts

Gaseous air pollutants emitted from anthropogenic sources are diverse and form secondary products through photochemical reactions, complicating the regulatory analysis of anthropogenic emissions in the atmosphere. Here, we used an environmental chassis dynamometer and a photochemical smog chamber to conduct a parameter sensitivity experiment to investigate the formation of secondary products from a direct-injection gasoline passenger car. To simulate the mitigation of ammonia (NH3) emissions from gasoline vehicle exhausts assuming future emission controls and to allow photochemical oxidation and aging of the vehicle exhaust, NH3 was selectively removed by a series of five denuders installed between the vehicle and the photochemical smog chamber. Overall, there were no differences in the formation of secondary organic aerosols and ozone with or without NH3 mitigation. However, the secondary particle formation potential of ammonium nitrate (NH4NO3) was significantly reduced with NH3 mitigation. In addition, NH3 mitigation resulted in increased particle phase acidity due to HNO3 in the gas phase not being neutralized by NH3 and condensing onto the liquid particle phase, indicating a potentially important secondary effect associated with NH3 mitigation. The present study provides new insights into the effects of NH3 mitigation on secondary emissions from gasoline vehicle exhaust and the experimental approach.