Abstract: Nitrophenols (NPs) are a common type of nitrogen-containing organic components in atmospheric aerosols. Aromatic compounds such as benzene and toluene from vehicle exhaust and other anthropogenic sources can undergo atmospheric chemical reactions and secondary formation of NPs. The atmospheric chemical process for photooxidation of benzene in presence of sodium nitrate (NaNO3) fine particles to form secondary organic aerosol (SOA) was simulated with smog chamber in this study. The on-line measurement of chemical components of benzene SOA was studied by using synchrotron radiation vacuum ultraviolet photoionization aerosol mass spectrometer (VUV-PIAMS). Based on the photoionization mass spectra and the photoionization efficiency curves of ion peaks detected by VUV-PIAMS, the ionization potentials were obtained for qualitative analysis of the chemical components. The experimental results demonstrated that in presence of NaNO3 fine particles, the mass of SOA produced by benzene photooxidation significantly increased. The photoionization mass spectra of SOA showed new peaks with m/z=139, 155, 171, 184, and 200, and the ionization potentials of these peaks were 8.81 ± 0.03, 9.36 ± 0.03, 8.68 ± 0.03, 8.75 ± 0.03, 9.55 ± 0.03, and 9.17 ± 0.03 eV, respectively. Combining quantum chemical calculations, it was analyzed and identified that NPs such as nitrophenol, nitrocatechol, nitropyrogallol, dinitrophenol and dinitrocatechol were main components of benzene SOA in presence of NaNO3 fine particles. These provide the experimental basis for source identification and formation mechanism study of NPs components in atmospheric SOA particles under the background of the presence of NaNO3 fine particles.

Key words: Nitrophenols, Benzene; Secondary organic aerosol, Synchrotron radiation, Photoionization mass spectra