A major uncertainty in scientific understanding of the global methane budget is the fraction of atmospheric methane lost via oxidation by the chlorine radical (Cl). Estimates of the importance of this loss process vary by over a factor of 30, limiting scientists’ ability to understand how changes to chlorine levels might affect future methane concentration. This project aims to improve scientific understanding of the importance of chlorine-initiated oxidation, via laboratory studies of reactions of Cl radicals with volatile organic compounds. Experiments will be carried out under reaction conditions relevant to the remote atmosphere and will center on aerosol formation as well as the identification and quantification of long-lived Cl-containing products which can serve as tracers for atmospheric chlorine chemistry.