QSPR-based estimation of the atmospheric persistence for chloronaphthalene congeners

Gas phase reaction with OH radicals is the major atmospheric loss process for the aromatic hydrocarbons. Thus, we used the half-live values (t1/2) derived based on this mechanism for characterization of environmental persistence and long-range atmospheric transport (LRAT) potential of all 75 chloronaphthalene congeners (CNs). We applied the single-media LRAT criterion from the Stockholm Convention (t1/2 in air > 2 days and vapor pressure < 1000 Pa). The values of t1/2 were estimated from a robust and predictive quantitative structure–property relationship (QPSR) model. The average half-lives for particular homologue groups of CNs were as following: 2 days for mono-CNs, 5 days for di-CNs, 10 days for tri-CNs, 19 days for tetra-CNs, 39 days for penta-CNs, 79 days for hexa-CNs, 163 days for hepta-CNs, and 343 days for octa-CN. Main factors affecting the persistence of chloronaphthalenes were the degree of chlorination and the substitution pattern. The congeners having the –C(β)Cl–C(α)H–C–C(α)Cl– fragment, in which relatively low electron density was observed on the α hydrogen and carbon atoms, were characterized by significantly lower half-lives than the rest of the compounds within the individual homologue groups.