Kinetics of aqueous phase reactions related to ozone depletion in the Arctic troposphere: Bromine chloride hydrolysis, bromide ion with ozone, and sulfur(IV) with bromine and hypobromous acid
Abstract
Aqueous phase halogen reactions play an important role in tropospheric ozone depletion that is observed during Arctic sunrise where bromine chloride is a key intermediate. The temperature dependencies of BrCl(aq) equilibration with BrCl2−, HOBr(aq ), Br2(aq), Cl2(aq ), HOCl(aq), Br−, and other species (Br3−, Br2Cl− , Cl3−, OBr− and OCl−) are determined as a function of [Cl −] concentration and pH. The kinetics of the very rapid BrCl( aq) hydrolysis are measured with the pulsed-accelerated-flow spectrometer. The reaction between ozone and Br− can lead to the generation of Br2(aq) and BrCl(aq) in darkness before polar sunrise and is potentially very important in the ozone depletion event. This reaction is specific-acid-assisted and is highly temperature dependent. A mechanism is proposed in which BrOOO− forms as a steady-state intermediate, which subsequently react with H+ and H2 O to give HOBr and O2. Both the water path rate constant and proton path rate constant are resolved. The chemistry of S(IV) is of concern in the ozone depletion process since Arctic aerosols contain sulfuric acid and S(IV) in solution can destroy HOBr and Br2(aq) by reducing them to Br−. The very rapid reactions of HOBr and Br2/Br3− with HSO 3− are investigated. Mechanisms are proposed with the following common features: (1) the reactions proceed through Br + transfer to form a BrSO3− intermediate; and (2) BrSO3− hydrolyzes rapidly to yield Br− and HSO4−. Rate constants for the reactions between Br2/Br3 − and HSO3− are resolved.
Degree
Ph.D.
Advisors
Margerum, Purdue University.
Subject Area
Analytical chemistry|Environmental science|Atmospheric sciences
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