Primary particulate emissions and secondary organic aerosol (SOA) formation from idling diesel vehicle exhaust in China

•Primary and secondary OA of diesel exhaust characterized with a smog chamber.•Much higher primary and secondary OA from diesel vehicles than gasoline ones•Higher diesel vehicle primary emission and secondary production of OA in China•Traditional precursor VOCs explained less than 3% SOA formed during aging.•Particle number emission factors of 0.65-4.0 × 1015 # kg-fuel− 1 for diesel vehicles

In China diesel vehicles dominate the primary emission of particulate matters from on-road vehicles, and they might also contribute substantially to the formation of secondary organic aerosols (SOA). In this study tailpipe exhaust of three typical in-use diesel vehicles under warm idling conditions was introduced directly into an indoor smog chamber with a 30 m3 Teflon reactor to characterize primary emissions and SOA formation during photo-oxidation. The emission factors of primary organic aerosol (POA) and black carbon (BC) for the three types of Chinese diesel vehicles ranged 0.18-0.91 and 0.15-0.51 g kg-fuel− 1, respectively; and the SOA production factors ranged 0.50-1.8 g kg-fuel− 1 and SOA/POA ratios ranged 0.7-3.7 with an average of 2.2. The fuel-based POA emission factors and SOA production factors from this study for idling diesel vehicle exhaust were 1-3 orders of magnitude higher than those reported in previous studies for idling gasoline vehicle exhaust. The emission factors for total particle numbers were 0.65-4.0 × 1015 particles kg-fuel− 1, and particles with diameters less than 50 nm dominated in total particle numbers. Traditional C2-C12 precursor non-methane hydrocarbons (NMHCs) could only explain less than 3% of the SOA formed during aging and contribution from other precursors including intermediate volatile organic compounds (IVOC) needs further investigation.

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