Atmospheric gas phase loss processes for chlorobenzene, benzotrifluoride, and 4-chlorobenzotrifluoride, and generalization of predictive techniques for atmospheric lifetimes of aromatic compounds

Abstract

The homogeneous gas phase atmospheric loss processes for chlorobenzene (CB), benzotrifluoride (BTF) and 4-chlorobenzotrifluoride (CBTF), compounds chemically and structurally similar to various classes of herbicides and pesticides currently in use, have been experimentally investigated by U.S. Environmental Protection Agency approved protocols. The rate constants, or upper limits thereof, for photolysis (under blacklight irradiation with an NO₂ photolysis rate of 0.27 min⁻¹) and reaction with OH radicals and O₃ were determined. The rate constants obtained were: k(photolysis) <2.7×10⁻⁶ sec⁻¹ for CBTF; k(O₃ reaction) <5×10⁻²¹ cm³ molecule⁻¹ sec⁻¹ for all three of these aromatic compounds; and k(OH radical reaction)=(8.8±1.1)×10⁻¹³ cm³ molecule⁻¹ sec⁻¹ for CB; (4.4±1.1)×10⁻¹³ cm³ molecule⁻¹ sec⁻¹ for BTF; and (2.3±0.8)×10⁻¹³ cm³ molecule⁻¹ sec⁻¹ for CBTF. Estimated atmospheric lifetimes due to these reactions are calculated and their environmental implications discussed. A predictive technique is presented for estimating the rate constants for addition of OH radicals to aromatic rings.