| Air-sea exchange has profound implications for biogeochemical cycling and climate. Sea-to-air transfer of the biologically produced dimethylsulfide (DMS) is of particular interest because the gas is a precursor to sulfate aerosols, which affect atmospheric chemistry and earth's radiative balance. In my dissertation, I discuss the air-sea exchange of DMS and the oxidation of DMS in the marine atmosphere. Chapter 1 provides background information on the formation of seawater DMS, theories behind air-sea exchange, oxidative destruction of DMS in the atmosphere, and the climatic impacts of sulfate aerosols. I also briefly describe our method for measuring DMS sea-to-air flux and provide an example of elevated DMS field near a front between two water masses. In Chapter 2, I compare air-sea transfer velocity measurements from the Southern Ocean to previous observations in temperate and tropical regions. I show that DMS transfer is suppressed in cold waters at high latitudes, not only due to reduced diffusivity, but also increased solubility. The transfer velocity of DMS is lower than those of the less soluble gases also because of this solubility effect. I shift my focus to biogeochemistry in the stratocumulus clouds topped Southeast Pacific in Chapter 3 and 4. In Chapter 3, based on shipboard and aircraft measurements, I estimate an average effective hydroxyl radical concentration from the budget analysis of DMS. In Chapter 4, I use a similar budget approach to analyze the diel cycles of sulfur dioxide and sulfate aerosols. I find that the dynamics of the boundary layer, which alternates from being coupled at night to decoupled during the day, significantly affects observed chemical concentrations. I also provide examples of recent particle formation observed on the ship and aircraft, which were often associated with drizzle events and open cell structures in the clouds. Along with results from Chapter 3, I summarize the atmospheric sulfur cycling in the Southeast Pacific. While oxidized sulfur species from pollution emissions dominate the near shore region, DMS still supplies most of the sulfur mass, and at times new particle number, to the remote marine boundary layer. |
