Impact of Propene on Secondary Organic Aerosol Formation from m-Xylene

Propene is widely used in smog chamber experiments to increase the hydroxyl radical (OH) level based on the assumption that the formation of secondary organic aerosol (SOA) from parent hydrocarbon is unaffected. A series of m-xylene/NO_x photooxidation experiments were conducted in the presence of propene in the University of California CE-CERT atmospheric chamber facility. The experimental data are compared with previous m-xylene/NO_x photooxidation work performed in the same chamber facility in the absence of propene (Song et al. Environ. Sci. Technol. 2005, 39, 3143−3149). The result shows that, for similar initial conditions, experiments with propene have lower reaction rates of m-xylene than those without propene, which indicates that propene reduces OH in the system. Furthermore, experiments with propene showed more than 15% reduction in SOA yield compared to experiments in the absence of propene. Additional experiments of m-xylene/NO_x with CO showed similar trends of suppressing OH and SOA formation. These results indicate that SOA from m-xylene/NO_x photooxidation is strongly dependent on the OH level present, which provides evidence for the critical role of OH in SOA formation from aromatic hydrocarbons.