Characterization of nitrated polycyclic aromatic hydrocarbons in secondary organic aerosol derived from photooxidation of naphthalene in the presence of NO2

Abstract

Nitrated Polycyclic aromatic hydrocarbons (NPAHs) widely exist in atmospheric aerosol particles are important constituents of brown carbon. Naphthalene and other polycyclic aromatic hydrocarbons (PAHs) are vital precursors of NPAHs. The NPAHs components of secondary organic aerosol (SOA) generated by the photooxidation of naphthalene under different concentrations of NO2 in chamber are on-line measured using synchrotron radiation vacuum ultraviolet photoionization aerosol mass spectrometer (VUV-PIMS) and verified off-line with optical spectrometry in this study. The results demonstrate that NO2 can promote the generation of NPAHs and formation of SOA. Using VUV-PIMS on-line detection, and combined with off-line UV-Vis and infrared spectroscopy verification, it is determined that carboxyls and naphthols are main components of naphthalene SOA particles without NO2, and nitro-naphthalene, dinitro-naphthalene, nitro-naphthol and dinitro-naphthol via the nitration of OH-naphthalene adduct and naphthol products of naphthalene are identified as principal constituents of SOA with NO2. The increase of strong chromophore of N = O of nitro group in NPAHs strengthens the absorbing ability of naphthalene SOA particles. The averaged mass absorption coefficient (< MAC>) over 200–600 nm of naphthalene SOA particles is increases gradually with the increasing concentration of NO2. The < MAC > of naphthalene SOA particles with 1000 ppb NO2 is 688 cm2/g, which is close to to that of biomass burning organic aerosol particles. These results offer the reference for exploring the formation mechanism and optical properties of NPAHs under the background of high concentration of NOx in urban atmosphere.