Establishing Water's Role in the Mechanism of Atmospheric New Particle Formation

美国国家科学基金会化学部的环境化学科学项目资助斯托尼布鲁克大学的克里斯托弗约翰逊教授研究直接从地球大气中的气体中形成的称为气溶胶的新粒子。这是一个重要的过程，但没有完整的框架来预测颗粒的形成和生长速率。 特别是，水在这些过程中的作用是未知的，因为很难在新粒子中检测到它的存在和结构。 该项目的重点是分离具有精确已知成分的“种子”粒子，并在精确控制的条件下在质谱仪内生长它们。这允许一次跟踪一个分子的组成的确切变化。 控制水蒸气压以确定它是否加速生长。分析含有水的分子簇以确定速率增加的原因。 这项工作确定了水如何影响颗粒形成，并为预测颗粒形成速率的理论研究提供了关键的比较。 这将最终有助于减少全球气候模型的不确定性。该项目为研究生提供培训和研究机会。 此外，约翰逊教授和他的学生通过粒子形成云的演示和可视化来向更广泛的公众进行宣传。该项目直接解决了水对新颗粒形成的机械影响。 使用变温离子阱质谱技术，生长的动力学和能量学的确定精确指定的种子簇组成的硫酸和一组有机酸和胺碱，在存在或不存在水。 三个假设正在测试中：（1）水作为一个“牺牲配体”，增强了进入蒸汽的粘附。 (2)水通过协同氢键稳定表面结合的分子。 (3)水通过降低现有簇的结构重排的障碍来催化生长，以容纳进入的蒸汽。 种子和产品集群的关键结构特征，其特征在于在原位振动光谱，以确定最活跃的网站的增长。 这项工作是与模拟颗粒生长的理论家合作进行的。实验可以验证的理论方法和计算提供了额外的见解实验结果。 该项目预计将产生更好的增长率预测，明确包括水，可以适应区域气候模型。除了为学生提供培训和研究机会外，约翰逊教授还计划与斯托尼布鲁克的艾伦阿尔达中心就促进科学传播进行互动。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

The Environmental Chemical Sciences Program of the NSF Division of Chemistry funds Professor Christopher Johnson at Stony Brook University to study the formation of new particles, called aerosols, directly from gases in the Earth's atmosphere. This is an important process, but no complete framework exists to predict particle formation and growth rates. In particular, the role of water in these processes is unknown, because it is difficult to detect its presence and structure in new particles. This project focuses on isolating "seed" particles with precisely known composition and growing them in inside a mass spectrometer under precisely controlled conditions. This allows the exact changes in composition to be followed one molecule at a time. Water vapor pressure is controlled to determine whether it speeds up growth. Molecular clusters containing water are analyzed to determine the cause of the rate increase. This work establishes how water impacts particle formation and provides critical comparisons for theoretical efforts to predict particle formation rates. This will ultimately help to reduce uncertainties in global climate models. The project provides training and research opportunities for graduate students. In addition, Professor Johnson and his students engage in outreach to the broader public through demonstrations and visualizations of particles forming clouds. This project directly addresses the mechanistic impacts of water on new particle formation. Using variable-temperature ion trap mass spectrometry techniques, the kinetics and energetics of growth are determined for precisely specified seed clusters consisting of sulfuric acid and a set of organic acids and amine bases, in the presence or absence of water. Three hypotheses are being tested: (1) Water serves as a "sacrificial ligand" that enhances the sticking of incoming vapors. (2) Water stabilizes surface-bound molecules through cooperative hydrogen bonding. (3) Water catalyzes growth by lowering the barrier to structural rearrangement of the existing cluster to accommodate incoming vapors. The critical structural features of seed and product clusters are characterized by in situ vibrational spectroscopy to determine the most active sites for growth. This work is carried out in collaboration with theoreticians modeling particle growth. The experiments can validate the theoretical approaches and the calculations provide additional insights into experimental results. This project is expected to yield enhanced predictions of growth rates, explicitly including water, that can be adapted to regional climate models. In addition to providing training and research opportunities to students, Professor Johnson also plans to interact with the Alan Alda Center at Stonybrook on promoting science communication.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.