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

Summary, in English

Gasoline vehicles have elevated emissions of volatile organic compounds during cold
starts and idling and have recently been pointed out as potentially the main source
of anthropogenic secondary organic aerosol (SOA) in megacities. However, there is
5 a lack of laboratory studies to systematically investigate SOA formation in real-world
exhaust. In this study, SOA formation from pure aromatic precursors, idling and cold
start gasoline exhaust from one Euro II, one Euro III and one Euro IV passenger vehicles were investigated using photo-oxidation experiments in a 6 m3
smog chamber.
The experiments were carried out at atmospherically relevant organic aerosol mass
10 concentrations. The characterization methods included a high resolution aerosol mass
spectrometer and a proton transfer mass spectrometer. It was found that gasoline exhaust readily forms SOA with a signature aerosol mass spectrum similar to the oxidized
organic aerosol that commonly dominates the organic aerosol mass spectra downwind
urban areas. After 4 h aging the formed SOA was 1–2 orders of magnitude higher than
15 the Primary OA emissions. The SOA mass spectrum from a relevant mixture of traditional light aromatic precursors gave f 43 (mass fraction at m/z = 43) approximately
two times higher than to the gasoline SOA. However O : C and H : C ratios were similar
for the two cases. Classical C6–C9
light aromatic precursors were responsible for up to
60 % of the formed SOA, which is significantly higher than for diesel exhaust. Impor20 tant candidates for additional precursors are higher order aromatic compounds such
as C10, C11 light aromatics, naphthalene and methyl-naphthalenes.