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。该项目的重点是推进对大气冰成核关键问题的理解，这是影响降水和影响冷云辐射特性的最基本过程之一。对云中冰形成过程的不完全了解导致云和降水的模拟能力存在很大的不确定性。在先前的支持下，首席研究员在非均质冰核（in）的实时测量领域取得了进展，并了解了能够在大气中引发冰形成的不同气溶胶颗粒类型的作用。这些测量结果突出了仍然存在的重要问题。例如，大气研究强调了矿物粉尘作为一个重要的IN来源的重要性，但对大小达1微米的天然粉尘颗粒的实验室研究表明，没有证据表明在温度高于-15摄氏度的情况下存在IN活动。在大气中已确定的第二种最普遍的IN成分是碳质颗粒，但其来源尚未确定。生物气溶胶是主要含碳素的潜在来源，但现有的测量方法很难观察到它们的数量浓度。最后，已经观察到污染空气中IN效率的明显退化，但对于理解大气处理对IN活化的影响几乎没有基本基础。主要研究人员将使用实验室研究来调查5微米大小的天然粉尘形成的冰，以量化不同矿物学类型的IN活化温度和矿物粉尘粒径之间的关系。他们还将量化暴露于实际程度的大气处理后in活化特性的变化。通过应用一种新的粒子相位辨别探测器（PPD），可以在pi的连续流冰核仪器中检测作为冰核的超微米大小的粒子，该探测器通过它们的空间散射模式而不仅仅是光学尺寸来识别冰晶和气溶胶粒子。PPD的使用将允许探索含IN液滴蒸发对冰成核的影响，这是由于推断该过程产生初级或次级冰成核而引起的兴趣。pi将通过使用实时IN检测器和应用实时质谱或对活化和收集的IN进行微生物方法（DNA分析）后应用的研究来调查生物冰核的数量浓度。使用这种方法，在特定的温度和湿度条件下识别出in活性细菌，从而能够评估它们在对流层云的整个温度范围内的作用。在通过实验室研究完善程序后，pi将应用这些方法来量化环境中生物来源的IN的比例，作为温度的函数。也有机会识别迄今为止未被识别的生物IN。该项目的智力价值在于有机会确认和增强目前对云中冰起冰的理解和量化，以及它与冰核关键大气源种群的具体性质的关系。pi将通过与大气相关的尺寸和温度范围内的IN来量化冰的形成，应用先进的技术来检测IN成分，确定大气处理对IN活化的影响，并探索冰的形成机制。利用本研究的结果，可以促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结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。pi将鼓励通过相关建模研究、与其他研究人员合作以及参与工作组来应用结果。研究生和一名博士后科学家将参与其中，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、出版物和参加会议来传播。最后，这些数据对于尚未解决的气溶胶对冰云和全球气候的影响至关重要。

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.