Measurements of gas phase hydrogen peroxide and methylhydroperoxide will be made in the marine boundary layer (MBL) over the equatorial Pacific upwind of Christmas Island, Kiribati, as part of the Pacific Atmospheric Sulfur Experiment (PASE). PASE is a comprehensive study of marine sulfur chemistry in the remote lower marine troposphere to be conducted in August-September 2007 on the NSF/NCAR C-130 aircraft. In collaboration with the Georgia Tech modeling effort, a chemistry mechanism including bulk aerosol chemistry, cloud droplets, gas phase chemistry, and parameterized gas-aerosol mass transport and material fluxes between the free troposphere-MBL and air-ocean surface will be implemented for the analysis and interpretation of the peroxide data. The mechanism will include halogens, bromine in particular. During PASE, sulfur species are expected to be regulated by the flux of dimethylsulfide (DMS) from the ocean and its subsequent oxidation. Critical to understanding the influence of marine sulfur gases on new particle production, particle growth, cloud-condensation nuclei and hence climate, are the production and fate of sulfur dioxide, dimethylsulfoxide, and sulfate from DMS. Peroxides are an important in-cloud oxidant of sulfur compounds. The PASE measurements and modeling of peroxides will provide constraints on meteorologically-driven material fluxes and on direct oxidants such as hydroxyl radical (OH) and hydrogen peroxide. This work will also constrain suspected oxidants like bromine monoxide (BrO), a potentially significant DMS oxidizer in the equatorial Pacific at its expected (0.05-0.5 ppt) but currently unmeasurable levels.
Broader impacts of the study include education and training of graduate students, exposure of undergraduates to atmospheric chemistry research, and dissemination of new knowledge on atmospheric chemistry, marine aerosols and climate. Knowledge transfer will occur via publications and presentations to other scientists and the general public.
