EAGER: Characterization of Surface Tension During the Western Atlantic Climate Study (WACS)

海洋表面、海气界面和大气中涉及海洋有机物的物理化学相互作用对辐射传输和气候具有重要意义。目前对海洋表面的有机质动力学及其与波浪过程和海洋气溶胶产生的相互作用的理解，在很大程度上忽视了发生在破波泡羽和海面上的物理过程：地球系统模式中的气溶胶产生仅由风速参数化，而有机质通常与可观测参数（如叶绿素-a）联系在一起，而这些参数并不反映观测到的变率。在这些高度简化的方法中，目前的理解状态很差，这是由于缺乏(1)对海洋表面活性剂特征的相关观测和(2)捕捉相关非线性的可靠理论框架。海水OM表现出不同的表面活性剂特征，这是由营养物介导的微生物过程在表面混合层内和下造成的，受季节分层调节。这导致了一种假设，即存在与这些表面和深层DOC池相关的显著表面活性剂特征，这反映在观测到的新生海洋衍生气溶胶数量中。作为2012年8月由美国国家海洋和大气管理局和美国国家科学基金会资助的从马萨诸塞州波士顿到百慕大的巡航的一部分，它将测试这一假设，使用表面张力测量，结合对海水中原位表面活性剂的直接观察，以及一套大型的水柱、大气边界层和气溶胶特性的辅助测量。该EAGER奖项将特别支持最大气泡压力（MBP）方法的新应用，以表征天然空气-海水界面的表面张力。该方法包括测量一根细毛细管末端的气泡内的压力，该毛细管的大小和速率受控制，注入水柱。根据膜介导气泡的拉普拉斯方程，当气泡产生时，在毛细管尖端具有可变寿命的气泡的表面张力由表面活性剂从散装液体到气泡表面的扩散速率决定。探索性的MBP测量，如果成功，将代表着建立具有代表性的海洋表面活性剂地图的第一步，这将对大气科学家和化学海洋学家都很有用。这将证明在改进用于气候预测的地球系统模型以及直接影响商业和运输的海浪和天气预报模型方面具有价值。博士后学者将获得使用该方法的经验，并从参加由世界一流的大气化学家和海洋学家组成的研究巡航中受益。

Physicochemical interactions involving marine organic matter (OM) in the surface ocean, at the air-sea interface, and in the atmosphere have important implications for radiative transfer and climate. Current understanding of OM dynamics in the surface ocean and corresponding interactions with wave processes and marine aerosol production largely neglect the physical processes that occur within a wave-breaking bubble plume and at the sea surface: Aerosol production in Earth system models is parameterized by wind-speed alone, and OM is often prognostically linked to observable parameters such as chlorophyll-a, which do not reflect observed variability. The poor state of current understanding reflected in these highly simplified approaches results from the lack of (1) relevant observations of surfactant characteristics at the ocean surface and (2) a reliable theoretical framework that captures the associated non-linearity.Seawater OM exhibits variable surfactant characteristics, which result from nutrient-mediated microbial processes in and below the surface mixed layer, modulated by seasonal stratification. This leads to the hypothesis that there is a significant surfactant signature associated with these surface and at-depth DOC pools that is reflected in the observed population of nascent ocean-derived aerosols. It is to test this hypothesis as part of a NOAA- and NSF-funded cruise from Boston, MA to Bermuda during August 2012 using measurements of surface tension in conjunction with direct observation of in situ surfactants in seawater and a large suite of ancillary measurements of water column, atmospheric boundary layer, and aerosol properties.This EAGER award will specifically support novel application of the maximum bubble pressure (MBP) method to characterize surface tension at the natural air-seawater interface. The method involves measuring pressure within gas bubbles at the end of a fine capillary tube of a controlled size and rate injected into the water column. The surface tension for bubbles with variable lifetimes at the capillary tip as the bubbles are generated is governed by the diffusion rate of surfactants from the bulk liquid to the bubble surface, based on the Laplace equation for a film-mediated bubble. The exploratory MBP measurements, if successful, will represent the first step toward building a representative map of ocean surfactants, which will be useful both to atmospheric scientists and chemical oceanographers. This will prove valuable in improving Earth system models used in climate prediction as well as ocean wave and weather forecast models that directly affect commerce and transportation. A postdoctoral scholar will gain experience with the method and benefit from participation on a research cruise with a world-class team of atmospheric chemists and oceanographers.