Dimethyl sulfide oxidation in the equatorial Pacific: Comparison of model simulations with field observations for

Abstract. Reported here are results from an airborne photochemical/sulfur field study in the equatorial Pacific. This study was part of NASA's Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM) Tropics A program. The focus of this paper is on data gathered during an airborne mission (P-3B flight 7) near the Pacific site of Christmas Island. Using a Lagrangian-type sampling configuration, this sortie was initiated under pre-sunrise conditions and terminated in early afternoon with both bound-ary layer (BL) as well as buffer layer (BuL) sampling being completed. Chemical species sampled included the gas phase sulfur species dimethyl sulfide (DMS), sulfur dioxide (SO2), methane sulfonic acid (MSA)•, and sulfuric acid (H2804),,. Bulk aerosol samples were collected and analyzed for methane sulfonate (MS), non-seaø-salt sulfate (NSS), Na +, CI-, and NH4 +. Critical non-sulfur parameters included real-time sampling of the hydroxyl radical (OH) and particle size/number distributions. These data showed pre-sunrise minima in the mixing ratios for OH, SO 2, and H2SO 4 and post-sunrise maxima in the levels of DMS, OH, and H2SO 4. Thus, unlike several previous tudies involving coinci-dence DMS and SO 2 measurements, the Christmas Island data revealed that DMS and SO