Strong emissions and aerosol formation potential of higher alkanes from diesel vehicles.

Higher alkanes are a major class of intermediate volatile organic compounds (IVOCs) emitted by vehicles, which have been considered as important precursors of secondary organic aerosol (SOA) in urban area. Dynamometer experiments were conducted to characterize emissions from gasoline and diesel vehicles in China. Three types of higher alkanes, namely acyclic, cyclic, and bicyclic alkanes, were explicitly quantified through the novel proton transfer reaction time-of-flight mass spectrometer with NO ionization (NO PTR-ToF-MS) with time response of 1 second. We show that higher alkanes from gasoline vehicles are mainly associated with initial engine start period, whereas emissions of higher alkanes from diesel vehicles are persistent during driving. Therefore, total emissions from diesel vehicles are substantially larger than gasoline vehicles. Our results indicate that over half of organic emissions from diesel vehicles are higher alkanes (56.9 %), with similar fractions for acyclic, cyclic, and bicyclic alkanes. The contributions of higher alkanes in OH reactivity (62.0 %) and SOA formation potential (97.6 %) for diesel emissions of organic compounds further emphasize the importance of higher alkanes. Our findings provide new insights on vehicular emissions of organic compounds, and the emission information should be included in future emission inventory and air quality models.