Temperature dependent kinetics of the OH/HO{sub 2}/O{sub 3} chain reaction by time-resolved IR laser absorption spectroscopy

This paper presents an extensive temperature dependent kinetic study of the catalytic HO{sub x} ozone cycle, (1) OH + O{sub 3} {r_arrow} HO{sub 2} + O{sub 2} and (2) HO{sub 2} + O{sub 3} {r_arrow} OH + 2 O{sub 2}, based on time-resolved, Doppler limited direct absorption spectroscopy of OH with a single mode ({Delta}{nu} = 0.0001 cm{sup {minus}1}) high-resolution infrared laser. The sum of the two chain rate constants, k{sub 1} + k{sub 2}, is measured over the 190--315 K temperature range and can be accurately described by an Arrhenius-type expression: k{sub 1} + k{sub 2} (cm{sup 3}/s) = 2.26(40) x 10{sup {minus}12} exp[{minus}976(50)/T]. These results are in excellent agreement with studies by Ravishankara et al. and Smith et al. but are significantly higher than the values currently accepted for atmospheric modeling. In addition, these studies also reflect the first such rate measurements to access the 190--230 K temperature range relevant to kinetic modeling of ozone chain loss in the lower stratosphere.