Concentrations of non-sea salt sulfate (NSS), methane sulfonate (MSA), and other aerosol species in the tropical marine boundary layer (MBL) will be measured from the NSF/NCAR C-130 aircraft, as part of the Pacific Atmospheric Sulfur Experiment (PASE). PASE is a comprehensive study of the sulfur chemistry that connects dimethyl sulfide (DMS) emissions from the ocean to aerosol formation and growth; it will take place near Christmas Island in the Equatorial Pacific in August/September 2007. Integrating filter and impactor collections will be used to accurately measure aerosol composition as a function of particle size, altitude, and time of day. A total aerosol sampler (TAS) will produce a highly accurate and precise total concentration of each major ion. A micro-orifice impactor (MOI) will be used to study intensive quantities such as the ratio of NSS to sea salt in each size range. These methods are relatively slow but they have been shown in a previous Christmas Island experiment to be well suited to high-precision studies of diurnal variations in sulfur-containing aerosols. The aerosol composition measurements will be used together with gas-phase sulfur data to constrain the budgets of sulfur species. Key questions to be addressed are: Can daily increases in sulfate be quantified, and what fraction of emitted DMS becomes NSS and MSA?
Broader scientific impacts center on a better understanding of the marine sulfur cycle, which links biological processes, air-sea exchange, DMS photochemistry, aerosol formation and growth, cloud properties, and Earth's radiation budget. Closing the sulfur budget in a DMS- dominated area will provide a strong constraint to the marine aerosol modules used in climate models and could ultimately improve the accuracy of climate assessments. A graduate student will also participate in PASE.