Chemical structure based model to predict nitrate radical‒mediated degradation of saturated organic contaminants in troposphere

Abstract

Saturated organic contaminant in the troposphere is an important factor for air pollution. Nitrate radical (NO3•) oxidation is the dominant pathway to remove organic contaminants in the troposphere during nighttime. However, few previous studies have estimated the second−order rate constant (kNO3•) for NO3• oxidation of organic contaminants, which makes it difficult to predict the environmental risk. Therefore, this paper proposes a quick and simple chemical structure model based on the group contribution method (GCM) to predict kNO3• using 63 experimental data and 11 molecular fragment descriptors. A GCM model was developed using multiple linear regressions (MLR) and internally and externally validated, exhibiting robust stability and good predictive power (internal and external validation coefficients Qint2 = 0.92 and Qext2 = 0.85, respectively). The H−atom abstraction (HAA) pathway is the first step for NO3• oxidation of saturated organic contaminants, and organic contaminant containing electron‒rich atom groups can enhance NO3• oxidation rate. Three NO3• oxidation reaction mechanisms have been proposed previously, and the GCM model provided a quick, computationally cheap, and highly efficient tool to predict kNO3• for NO3• degradation, and help to understand the reaction mechanisms.