The reaction O(³P) + HOBr: Temperature dependence of the rate constant and importance of the reaction as an HOBr stratospheric loss process

The absolute rate constant for the reaction O(³P) + HOBr has been measured between T=233K and 423K using the discharge‐flow kinetic technique coupled to mass spectrometric detection. The value of the rate coefficient at room temperature is (2.5±0.6) × 10−11 cm³ molecule−1 s−1 and the derived Arrhenius expression is (1.4±0.5) × 10−10 exp[(−430±260)/T] cm³ molecule−1 s−1. From these rate data the atmospheric lifetime of HOBr with respect to reaction with O(³P) is about 0.6h at z = 25 km which is comparable to the photolysis lifetime based on recent measurements of the UV cross section for HOBr. Implications for HOBr loss in the stratosphere have been tested using a 1D photochemical box model. With the inclusion of the rate parameters and products for the O + HOBr reaction, calculated concentration profiles of BrO increase by up to 33% around z = 35 km. This result indicates that the inclusion of the O + HOBr reaction in global atmospheric chemistry models may have an an impact on bromine partitioning in the middle atmosphere.