Characterization of single scattering albedo and chemical components of aged toluene secondary organic aerosol

Secondary organic aerosol (SOA) can influence the radiative balance of the atmosphere via its optical properties. The single-scattering albedo (SSA) and complex refractive index (RI) are the basic optical parameters of the aerosol particles. Toluene SOA particles were formation and aging with extreme amounts of OH radicals without NOx in flow reactor chamber in this study, cavity-enhanced aerosol single-scattering albedometer, UV–Vis spectrometer, and liquid chromatography-mass spectrometry (LC-MS) were utilized to measure the optical properties and components of the aged toluene SOA, respectively. Experimental results demonstrated that the retrieved real part of RI for aged toluene SOA was 1.452 ± 0.002, which is consistent with the reported data. The measured SSA of aged toluene SOA was 0.78 ± 0.02, slightly lower than that of organic aerosols associated with biomass burning (BBOA), and the k-value (imaginary part of RI, corresponding to the absorption extent of SOA particles) was 0.024 ± 0.002, larger than that of fresh toluene SOA, indicating that the absorbing ability of SOA increased with increasing oxidation level. The obtained UV absorption and electrospray ionization mass spectrum shown that carboxylic acids are identified as the principal constituents of aged toluene SOA, which are responsible for the decreased SSA and increased k-value measured by the albedometer when compared to the fresh SOA. As the rate of production of SOA is greater than that of BBOA, the aged SOA particles may contribute remarkably to the radiative balance of the atmosphere. These would provide experimental basis for refine the radiative forcing estimates of anthropogenic SOA for certain regions.