OH reaction kinetics of gas-phase α- and γ-hexachlorocyclohexane and hexachlorobenzene

Rate constants for the gas-phase reactions of the hydroxyl radical (OH) with alpha- and gamma-hexachlorocyclohexane (alpha- and gamma-HCH) and hexachlorobenzene (HCB) were measured over the temperature range 346-386 K. The experiments were carried out in He diluent gas at approximately 1 atm, in a 160-mL quartz chamber. OH was produced by the photolysis of ozone in the presence of H2O, and reactants in the chamber were monitored by online mass spectrometry. The rate constants measured at elevated temperatures were extrapolated by the Arrhenius equation, and OH reaction rate constants at 298 K were estimated for each compound. These rate constants at 298 K (in units of 10(-13) cm(3) s(-1)) were alpha-HCH, 1.4; gamma-HCH, 1.9; and HCB, 0.27. Atmospheric lifetimes based on OH reactions (tau(OH)) were also estimated (in units of days): alpha-HCH, 120; gamma-HCH, 96; and HCB, 940. These relatively high atmospheric lifetimes indicate that these compounds can be transported great distances through the atmosphere before removal processes associated with the global distillation effect.