Photochemical transformation and secondary aerosol formation potential of Euro6 gasoline and diesel passenger car exhaust emissions

Abstract

Traffic remains a major source of urban air pollution although emission regulations have led to significant reductions in exhaust emissions of new vehicles. In this work the photochemical transformation of exhaust emissions from gasoline and diesel passenger vehicles compliant with the current European ‘Euro6’ emission standard and operated with traditional and alternative fuels was investigated using an environmental chamber. By assessing four different engine operation conditions, we show that vehicle operation notably affects the exhaust composition and secondary aerosol formation potential. For the gasoline vehicle, secondary aerosols dominate the total particulate emissions. In contrast, we observe no substantial secondary aerosol formation for exhaust emissions of a Euro6-level diesel vehicle. High engine load operation and cold start of the gasoline vehicle led to 11–470-fold particulate mass enhancement, while for moderate driving conditions the enhancement ratio was below 2. High aerosol enhancements also led to strong increases in particle light absorption. The results underline the necessity for future directives to include the emission components leading to secondary pollution, in addition to the freshly emitted pollutants. The link observed between secondary organic aerosol (SOA) formation and gaseous aromatic hydrocarbon emissions suggests that monitoring and limiting these gaseous species can provide an indirect regulation for SOA. Additionally, ammonia released as a byproduct of the gasoline vehicle is confirmed as an important precursor for secondary aerosols.