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

海洋有机物（OM）在海洋表面、海气界面和大气中的物理化学相互作用对辐射传输和气候有重要影响。目前对海洋表面OM动力学以及与波浪过程和海洋气溶胶产生的相应相互作用的理解在很大程度上忽略了发生在破波气泡羽流和海面的物理过程：地球系统模型中的气溶胶产生仅由风速参数化，OM通常与可观察参数（如叶绿素a）相关，而这些参数并不反映观察到的变化。反映在这些高度简化的方法，目前的理解状态差的结果缺乏（1）在海洋表面的表面活性剂特性的相关观测和（2）一个可靠的理论框架，捕捉相关的非线性。海水OM表现出可变的表面活性剂的特性，这是由于营养介导的微生物过程中和以下的表面混合层，季节性分层调制。这导致的假设，有一个显着的表面活性剂签名与这些表面和深度DOC池，反映在观察到的人口的新生海洋气溶胶。作为2012年8月期间NOAA和NSF资助的从马萨诸塞州波士顿到百慕大的巡航的一部分，使用表面张力测量结合海水中原位表面活性剂的直接观察以及水柱、大气边界层、EAGER奖将特别支持最大气泡压力（MBP）方法在天然空气-海水界面表征表面张力的新应用。该方法涉及测量气泡内的压力，该气泡位于注入到水柱中的受控尺寸和速率的细毛细管的末端。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本体液体到气泡表面的扩散速率决定，基于膜介导的气泡的拉普拉斯方程。探索性的MBP测量，如果成功的话，将是建立海洋表面活性剂的代表性地图的第一步，这将是有用的大气科学家和化学海洋学家。这将证明对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很有价值。一名博士后学者将获得该方法的经验，并与世界一流的大气化学家和海洋学家团队一起参加研究巡航。

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.