Important role of aromatic hydrocarbons in SOA formation from unburned gasoline vapor

Abstract

Gasoline emissions are the largest source of urban atmospheric VOCs, which are critical precursors of ozone (O3) and secondary organic aerosol (SOA). Besides vehicle exhaust, emissions from gasoline evaporation also have a potentially significant effect on SOA formation. However, there are still few studies on the relationship between gasoline vapor composition and SOA formation, especially for gasoline in China. In this study, SOA formation from three unburned gasoline vapors were investigated in a 30 m3 indoor smog chamber. The experimental results showed that with the increase of aromatic content (especially toluene and C2 benzenes) in gasoline from 23% to 50%, the SOA yield was significantly enhanced by a factor of 4.0–6.7. This phenomenon might be related to the higher amounts of intermediate volatility organic compounds (IVOCs) and semi-volatile organic compounds (SVOCs) formed, which promoted the gas-particle partitioning and SOA formation. Additionally, the synergistic effects between precursors in the mixtures might also be a key factor, which could be supported by the higher SOA yield accompanied by a higher ratio of toluene/benzene. Meanwhile, there were more oxygenated organic aerosols (OOA) observed when using high-aromatic gasoline. This work will help in understanding the effect of aromatic content or gasoline quality on the SOA formation from gasoline evaporation emissions, and in providing the scientific basis for taking corresponding control measures to relieve haze events in China.