Experimental Study on Composition and Optic of Secondary Organic Aerosol Generated by Aqueous Photoxidation of Toluene in Presence of Copper Ions

Toluene and other aromatics can dissolve in atmospheric aqueous phases and undergo photooxidation reactions, forming secondary organic aerosol (SOA) after water evaporation. Copper ion is a typical heavy metal ion and is able to change the composition and optics of SOA. The reaction solution for OH-initiated photooxidation of toluene in presence of copper ions is atomized by TSI 9302, and the water is absorbed by silica gel to simulate the formation of aqueous SOA particles in this study. The composition and optics of the formed aqueous SOA are on-line and off-line, characterized by mass spectrometry and spectroscopy. Experimental results demonstrate that laser desorption/ionization mass spectra for aqueous SOA contain molecular ion peaks at m/z = 108, 124, and 140 for cresol, mehtyl dihydroxybenzene, and methyl trihydroxybenzene. The absorption peak intensity of phenolic compounds at 277 nm in the UV-Vis spectra of the collection solution for aqueous SOA increases, and electrospray ionization negative ion mass spectra show the polymer ion peak as high as m/z = 641. These indicate that copper ions catalyze the production of more phenolic compounds and hydroxyphenyl ether polymers formed by the polymerization of cresol. These products have the capacity for strong light absorption, leading to a significant increase in the averaged mass absorption coefficient () in 200-600 nm for aqueous SOA, which gently rises with an increment of copper ions. These provide the basis for studying the components and optics of aqueous SOA in presence of heavy metal ions.