title: Methyl chloride and methyl bromide emissions from baking: an unrecognized anthropogenic source.
abstract: Methyl chloride and methyl bromide (CH3Cl and CH3Br) are the largest natural sources of chlorine and bromine, respectively, to the stratosphere, where they contribute to ozone depletion. We report the anthropogenic production of CH3Cl and CH3Br during breadbaking, and suggest this production is an abiotic process involving the methyl ester functional groups in pectin and lignin structural polymers of plant cells. Wide variations in baking styles allow only rough estimates of this flux of methyl halides on a global basis. A simple model suggests that CH3Br emissions from breadbaking likely peaked circa 1990 at approximately 200tonnes per year (about 0.3% of industrial production), prior to restrictions on the dough conditioner potassium bromate. In contrast, CH3Cl emissions from breadbaking may be of similar magnitude as acknowledged present-day CH3Cl industrial emissions. Because the mechanisms involve functional groups and compounds widely found in plant materials, this type of methyl halide production may occur in other cooking techniques as well.
authors.affiliation: Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden. Electronic address: brett.thornton@geo.su.se.
authors.forename: Brett F
authors.initials: BF
authors.lastname: Thornton
authors.affiliation: Department of Analytical Chemistry and Environmental Science, Stockholm University, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden.
authors.forename: Axel
authors.initials: A
authors.lastname: Horst
authors.affiliation: Department of Analytical Chemistry and Environmental Science, Stockholm University, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Carrizo
authors.affiliation: Bolin Centre for Climate Research, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden; Department of Analytical Chemistry and Environmental Science, Stockholm University, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden.
authors.forename: Henry
authors.initials: H
authors.lastname: Holmstrand
keywords: Breadbaking; Chloromethane; Methyl bromide; Methyl chloride; Ozone; Potassium bromate