Mechanism and kinetic properties of NO3-initiated atmospheric degradation of DDT

In this article, the NO₃ radical-initiated atmospheric oxidation degradation of DDT was theoretically investigated using molecular orbital theory calculations. All the calculations of intermediates, transition states and products were performed at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. Several energetically favorable reaction pathways were revealed. The formation mechanisms of secondary pollutants were presented and discussed. The rate constants were deduced over the temperature range of 273-333 K using canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) method. Our study shows that H abstraction from the alkyl group and NO₃ addition to the C₃ atom of the benzene ring are the dominant reaction pathways. The rate-temperature formula of the overall rate constants is k(T)(DDT+NO₃) = (7.21×10^-15)exp(-153.81/T) cm³/(mol.sec) over the possible atmospheric temperature range of 273-333 K. The atmospheric lifetime of DDT determined by NO₃ radical is about 52.5 days, which indicates that it can be degraded in the gas phase within several months.