Chemical analysis of nitro‐aromatic compounds of secondary organic aerosol formed from photooxidation of p‐xylene with NOx

Abstract

AbstractNitro‐aromatic compounds (NACs) measured in ambient aerosol are important contributors to brown carbon. Aromatic compounds are expected to be vital precursors of NACs in the presence of NOx in urban atmospheres. NACs of secondary organic aerosol (SOA) formed from photooxidation of p‐xylene with a variety of NO2 in smog chamber were investigated in this study. NACs were on‐line measured by aerosol laser time‐of‐flight mass spectrometer and verified by off‐line of ultraviolet absorption and electrospray ionization mass spectra. The results show that NO2 can promote the formation of p‐xylene SOA. Different from the carbonyls detected in p‐xylene SOA without NO2, nitrophenols, nitrocatechols, and other NACs via the nitration of phenolic products of p‐xylene are detected as the major components of SOA with NO2. The increase of electrophilic nitro groups in SOA strengthens absorption ability. The mass absorption coefficient averaged over 200–600 nm (<MAC>) of SOA gradually increased with the increasing of the concentration of NO2. The <MAC> of SOA with 1,000 ppb NO2 was comparable to that of biomass burning organic aerosols. These provided experimental basis for studying the formation mechanism and optics of anthropogenic NACs in the background of high concentration of NOx in Chinese urban atmosphere.