9627231 Abbatt In this project, experimental studies of heterogeneous processes involving halogen species important in determining the photochemical steady state of the troposphere will be performed. The majority of the work will focus upon aspects of bromine heterogeneous chemistry as it relates to the phenomenon of ozone depletion in the Arctic boundary layer in the springtime. Particular interactions to be studied are those of HOBr, HBr, BrO and brominated organic species with tropospheric particulate surfaces. The goal of these experiments is to better define the mechanism by which bromine is maintained in a form active towards gas-phase ozone destruction and to determine the dominant source of inorganic bromine. Motivated by observations which indicate large amounts of active chlorine during these ozone depletion events, studies of chlorine heterogeneous chemistry which may be an integral part of this phenomenon will also be carried out. Experimentally, these studies will be performed using a combination of experimental techniques. Gas-surface uptake coefficients and reaction probabilities will be measured both in a high pressure, aerosol flow tube recently constructed in this laboratory and in a standard low pressure, coated-wall flow tube. To determine the partitioning of brominated species between the gas and condensed phases, mass spectrometry will be used to measure the equilibrium vapor pressures of stable species dissolved in solutions and to measure the physical uptake of gas-phase species by thin films. Finally, FTIR absorption spectroscopy will be used to monitor the phase and composition of the aerosols within the aerosol flow tube. These experiments will be performed under conditions of aerosol composition, temperature and relative humidity which match as closely as possible those prevalent in the atmosphere. ***
