Collaborative Research: Laboratory and Ground-Based Studies Addressing Unresolved Aspects of Atmospheric Ice Nucleation

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。该项目的重点是促进对大气冰成核关键问题的了解，这是影响降水和影响冷云辐射特性的最基本过程之一。对云中冰的形成过程的不完全理解导致对云和降水进行模拟的能力存在很大的不确定性。在先前的支持下，首席调查员在实时测量非均质冰核和了解能够在大气中形成冰的不同气溶胶粒子类型的作用方面取得了进展。这些衡量突显了仍然存在的重大问题。例如，大气研究强调了矿物粉尘作为一种重要的IN来源的重要性，但对尺寸最大为1微米的天然粉尘颗粒的实验室研究表明，没有证据表明IN活动的温度高于约零下15摄氏度。大气中已确定的第二种最普遍的IN成分是碳质颗粒，但它们的来源尚不清楚。生物气溶胶主要是碳质IN的潜在来源，但现有的测量方法很难观察到它们的数字浓度。最后，在污染的空气中观察到了IN效率的明显下降，但对于了解大气处理对IN活化的影响几乎没有基本的依据。首席调查员将利用实验室研究，调查大小达5微米的天然粉尘形成的冰，以量化不同矿物学类型的IN激活温度与矿物粉尘颗粒大小之间的关系。他们还将量化在暴露于真实的大气处理程度后IN激活特性的变化。在PIS的连续流动冰核仪器中，通过应用一种新的粒子相位识别探测器(PPD)，可以检测作为冰核的超微米粒子，该探测器根据冰晶和气溶胶粒子的空间散射模式识别冰晶和气溶胶粒子，而不仅仅是光学尺寸。PPD的使用将允许探索含IN液滴的蒸发对冰核的影响，这是由于推断这一过程产生了初级或次级冰核。PIS将通过利用实时IN探测器的研究，以及对激活和收集的IN应用实时质谱仪或微生物方法(DNA分析)后的应用，来调查生物冰核的数量浓度。使用这种方法，可以在特定的温度和湿度条件下确定IN-Active细菌，从而能够评估它们在对流层云的整个温度区域中的作用。在通过实验室研究进行精炼程序后，PI将应用这些方法来量化环境中具有生物来源的IN的比例，作为温度的函数。也存在识别迄今未被识别的生物IN的机会。该项目的学术价值在于有机会确认和加强目前对云中冰的形成及其与冰核关键大气源群的具体性质的关系的理解和量化。PI将通过与大气相关的大小和温度范围内的IN来量化冰的形成，应用先进的技术来检测IN的成分，确定大气处理对IN激活的影响，并探索冰形成的机制。利用这项研究的结果，可以推进数值模拟研究的成核参数化发展。这项工作将通过促进研究生教育和培训，加强研究基础设施，开发和测试新的仪器和方法，通过相关的数值模拟研究将成果应用于全球气候变化问题，以及促进大气和生物科学之间的跨学科研究，产生更广泛的影响。绩效指标将通过相关的建模研究、与其他研究人员的合作以及参加工作组来鼓励成果的应用。研究生和博士后科学家将参与这项工作，这项工作将涉及多个学科和大学的合作。结果将通过项目网站、出版物和参加会议进行传播。最后，这些数据对于气溶胶对冰云和全球气候的悬而未决的影响至关重要。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project focuses on advancing understanding of critical issues in atmospheric ice nucleation, one of the most basic processes affecting precipitation and impacting the radiative properties of cold clouds. Incomplete understanding of ice initiation processes in clouds results in large uncertainties in the ability to model clouds and precipitation. Under prior support, the Principal Investigators (PIs) have made advancements in the area of real-time measurement of heterogeneous ice nuclei (IN) and in understanding the role of different aerosol particle types capable of initiating ice formation in the atmosphere. These measurements highlight significant remaining questions. For example, atmospheric studies have emphasized the importance of mineral dust as a significant IN source, but laboratory studies of natural dust particles up to 1 micron in size have shown no evidence for IN activity warmer than about -15 degrees Celsius. The second most prevalent IN composition that has been identified in the atmosphere are carbonaceous particles, but their sources are unresolved. Biological aerosols represent potential sources for primarily carbonaceous IN, but their number concentrations are poorly observed by existing measurement methods. Finally, apparent degradation of IN efficiency in polluted air has been observed but there is little fundamental basis for understanding the impacts of atmospheric processing on IN activation. The Principal Investigators will use laboratory studies to investigate ice formation by natural dusts at sizes up to 5 microns to quantify the relation between IN activation temperature and mineral dust particle size for different mineralogical types. They also will quantify the changes in IN activation properties after exposure to realistic degrees of atmospheric processing. Examinations of supermicron-sized particles as ice nuclei in the PIs' continuous flow ice nuclei instrument is made possible by application of a new particle phase-discrimination detector (PPD) that identifies ice crystals and aerosol particles by their spatial scattering patterns rather than optical size alone. Use of the PPD will permit exploration of the impact of evaporation of IN containing droplets on ice nucleation, of interest due to inferences that this process spawns primary or secondary ice nucleation. The PIs will investigate the number concentrations of biological ice nuclei through studies that utilize a real-time IN detector and application of real-time mass spectrometric or post-application of microbiological methods (DNA analyses) on activated and collected IN. Using this approach, IN-active bacteria are identified at specific temperature and humidity conditions, enabling an assessment of their role across the full temperature regime of tropospheric clouds. After refining procedures through laboratory studies, The PIs will apply these methods to quantify the proportion of ambient IN, as a function of temperature, that are of biological origin. The opportunity also exists to identify heretofore unrecognized biological IN. The intellectual merit of the project lies in the opportunity to confirm and augment present understanding and quantification of ice initiation in clouds and its relation to the specific properties of key atmospheric source populations of ice nuclei. The PIs will quantify ice formation by IN across their atmospherically-relevant size and temperature range, apply advanced techniques for detecting IN composition, determine the impacts of atmospheric processing on IN activation, and explore ice formation mechanisms. Nucleation parameterization development for numerical modeling studies may be advanced using results from this research. This work will have broader impacts through promoting graduate education and training, enhancing research infrastructure, development and testing of new instrumentation and methods, application of results toward global climate change issues through associated numerical modeling studies, and fostering cross-disciplinary research between the atmospheric and biological sciences. The PIs will encourage application of results through related modeling studies, collaboration with other researchers, and participation in working groups. Graduate students and a postdoctoral scientist will participate and the work will involve collaborations across multiple disciplines and universities. Results will be disseminated via a project web site, publications, and participation in conferences. Finally, these data are of critical importance to unresolved impact of aerosols on ice clouds and global climate.