Measuring Methyl Halide Fluxes in Temperate Grasslands Using Stable Isotope Tracers

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This project seeks to quantify fluxes of atmospheric methyl halides in temperate North American grassland ecosystems, employing a recently developed stable isotope tracer technique to separate simultaneous production and consumption fluxes. Methyl halides are major carriers of halogens in the atmosphere and consequently play important roles in stratospheric ozone chemistry. Field measurements will be conducted in three different types of grasslands ecosystems located in California, Colorado, and Kansas. The primary objectives of this work are: (1) to determine whether or not temperate grasslands are net sources or net sinks of methyl halides; (2) to separately quantify the production and consumption fluxes of methyl bromide and methyl chloride using a stable isotope tracer technique, and (3) to investigate the environmental, biological and biogeochemical drivers of the fluxes, ultimately improving our understanding of their atmospheric lifetimes and ozone depletion potentials.Four undergraduate students and a post-doctoral researcher will participate in this research. At least two undergraduate researchers will be from underrepresented groups in the sciences, as selected through the Berkeley Leadership Excellence through Advanced Degrees program. Methyl bromide is a broad-spectrum agricultural fumigant whose use is scheduled to be phased out in accordance with the Montreal Protocol. Understanding the biogeochemistry of methyl halides is prerequisite to understanding how changes in policy, climate, and land use will affect the halogen loading in the atmosphere.