Understanding the role of Cl and NO3 radicals in initiating atmospheric oxidation of fluorene: A mechanistic and kinetic study

Abstract

The photooxidation of volatile organic compounds (VOCs) initiated by Cl and NO3 radicals has been investigated for decades to assess the atmospheric fates of pollutants. Gas-phase fluorene is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) that can be oxidized by activated radicals. In this study, we used quantum chemical calculation to study the atmospheric degradation of fluorene initiated by Cl and NO3 radicals. The results showed that the Cl radical initiated reaction of fluorene mainly produces 9-fluorene radical that has significant potential to form secondary pollutants with more persistent toxic properties. The NO3 radical initiated reaction of fluorene leads to the formation of oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs) including nitrooxyfluorene, nitrooxyfluorenone and 1,4-fluorenequinone. The rate constants and branch ratios of elementary reactions were determined based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The atmospheric lifetime of fluorene determined by NO3 radical is deduced to be 1.52days according to the calculated overall rate constant, 1.52×10-14cm3 molecule-1s-1. The derivatives produced from the atmospheric degradation of fluorene initiated by Cl and NO3 radicals increase the environmental risks of fluroene. Combined with previous experimental and theoretical findings, this work can help to clarify the atmospheric fate and assess the environmental risks of fluorene.