Secondary organic aerosol formation from idling gasoline passenger vehicle emissions investigated in a smog chamber

摘要

Gasoline vehicles have recently been pointed out as potentially the mainsource of anthropogenic secondary organic aerosol (SOA) in megacities.However, there is a lack of laboratory studies to systematically investigateSOA formation in real-world exhaust. In this study, SOA formation from purearomatic precursors, idling and cold start gasoline exhaust from threepassenger vehicles (EURO2–EURO4) were investigated with photo-oxidationexperiments in a 6 m smog chamber. The experiments were carried outdown to atmospherically relevant organic aerosol mass concentrations. Thecharacterization instruments included a high-resolution aerosol massspectrometer and a proton transfer mass spectrometer. It was found thatgasoline exhaust readily forms SOA with a signature aerosol mass spectrumsimilar to the oxidized organic aerosol that commonly dominates the organicaerosol mass spectra downwind of urban areas. After a cumulative OH exposure of~5 × 10 cm h, the formed SOA was 1–2 orders ofmagnitude higher than the primary OA emissions. The SOA mass spectrum from arelevant mixture of traditional light aromatic precursors gave (), approximatelytwo times higher than to the gasoline SOA. However O : C and H : C ratios weresimilar for the two cases. Classical C–C light aromaticprecursors were responsible for up to 60% of the formed SOA, which issignificantly higher than for diesel exhaust. Important candidates foradditional precursors are higher-order aromatic compounds such as Cand C light aromatics, naphthalene and methyl-naphthalenes. We concludethat approaches using only light aromatic precursorsgive an incomplete picture of the magnitude of SOA formation and the SOAcomposition from gasoline exhaust.