Formation of oxidized organic compounds from Cl-initiated oxidation of toluene

The formation of secondary organic aerosol (SOA) from toluene can impact urban air quality and therefore human health. Most SOA studies have focused on OH chemistry; however recent work suggests that chlorine atoms (CI) may affect tropospheric chemistry more than previously assumed. This work focuses on SOA formation from Cl-initiated oxidation of toluene under different conditions. The fast reaction between Cl and toluene enabled complete consumption of toluene in environmental chamber experiments and aging of the toluene SOA. A high resolution time-of-flight chemical ionization mass spectrometer was used to observe several generations of gas-phase products. The presence of nitric oxides (NOx) appears to delay the formation of later generation products. Data from an aerosol chemical speciation monitor suggest that all SOA formed had high oxidation state, and that the bulk organic composition was different for SOA from Cl-dominated reactions compared to SOA from OH-dominated reactions. Addition of oxidant after all toluene had been consumed did not result in a significant change in the organic aerosol oxidation state, suggesting that the system may have reached an oxidative end-point in the particle phase.