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

EAGER：西大西洋气候研究 (WACS) 期间表面张力的表征

• 批准号: 1252755
• 负责人: Daniel Jacob
• 金额: $ 1.37万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1252755&HistoricalAwards=false
• 关键词: EAGER; Characterization; Surface; Tension; During

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.

表层海洋、海-气界面和大气中涉及海洋有机质的物理化学相互作用对辐射传输和气候具有重要影响。目前对表层海洋中的有机质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视了发生在破浪泡羽内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进行参数化，而有机质往往与叶绿素-a等可观测参数有预测性联系，而这些参数不能反映观测到的变异性。这些高度简化的方法反映出目前对表面活性剂认识不足的状况，原因是缺乏(1)海洋表面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。海水有机质表现出可变的表面活性剂特征，这些特征是受季节性层结调制的营养物质介导的表层混合层及其以下的微生物过程的结果。这导致了一种假设，即存在与这些表层和深层DOC池相关的显着表面活性物质特征，这反映在观测到的新生海洋气溶胶种群中。2012年8月，作为NOAA和NSF资助的从马萨诸塞州波士顿到百慕大的邮轮的一部分，它将通过测量表面张力并直接观测海水中的表面活性物质，以及对水柱、大气边界层和气溶胶性质的一大套辅助测量来验证这一假设。这项急切的奖项将特别支持最大气泡压力(MBP)方法的新应用，以表征自然空气-海水界面的表面张力。该方法包括测量注入水柱的毛细毛细管末端的气泡内的压力，毛细管的大小和速度受到控制。在气泡形成时，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大块液体到气泡表面的扩散速率控制，该扩散速率基于薄膜介导的气泡的拉普拉斯方程。如果成功，探索性的MBP测量将代表着朝着建立具有代表性的海洋表面活性剂地图迈出的第一步，这将对大气科学家和化学海洋学家都有用。这将被证明在改进气候预测中使用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。博士后学者将获得该方法的经验，并从与世界级大气化学家和海洋学家团队的研究巡航中受益。