Role of liquid water in the formation of O3 and SOA particles from 1,2,3-trimethylbenzene

Abstract

Aromatic volatile organic compounds (VOCs) are highly reactive in the formation of ozone (O3) and secondary organic aerosols (SOA). 1,2,3-trimethylbenzene (123-TMB) is an aromatic VOCs which is directly emitted to the atmosphere by motor vehicle exhaust emissions and the evaporation of solvents. In this study, a series of smog chamber experiments were conducted to compare the formation of O3 and SOA particles from photooxidation of 1,2,3-TMB by UV radiation, under various humidity conditions and NOx control conditions, in the presence and absence of NaCl seed particles. At a relative humidity of 86%, the hygroscopic growth factor (GF) of SOA generated from 123-TMB was 1.044. Conversely, with increasing liquid water content (LWC) from 0 to 85.0 μg m−3, O3 concentrations decreased from 468 ppb to 323 ppb and the yield of SOA increased from 3.0 to 14.7%, with initial NaCl concentrations of 11.0 ± 0.7 μg m−3. FT-IR results show that with increasing LWC, the major contributors to SOA were identified as alcohols and hydrates. These findings indicate that liquid water is an important factor in the formation of O3 and SOA.