Determining the Buffering Capacity and PH of Aerosols and Their Control of the Multiphase Chemical Evolution and Kinetics of Optically Levitated Particles

在化学系环境化学科学(ECS)项目的支持下，卡内基梅隆大学的瑞安·沙利文将利用光学镊子研究大气气溶胶。气溶胶是悬浮在空气中的微米大小的液体或固体颗粒。它们具有独特的化学性质和反应活性，因为它们具有较高的比表面积与体积比。大气气溶胶可以作为化学催化剂，加速化学反应，促进仅在气相中不能发生的水相化学。气溶胶表面的性质在控制气溶胶的化学反应及其对大气化学、空气质量、健康、云微物理和气候的诸多影响方面起着重要的作用。该项目将使用一种名为气溶胶光学镊子(AOT)的工具对悬浮液滴进行实验，以确定各种关键化学性质的演变。气溶胶酸度是一个重要的化学性质，它强烈地影响界面的化学和化学动力学。这些实验有望对颗粒组成、酸度和形态的变化产生新的化学理解，这些变化改变了这些复杂颗粒的反应性。除了培训研究生和本科生，沙利文博士还将在当地公立学校为6-12年级的学生创建和部署环境化学的动手实验和课程材料，这些学校服务于大量未被充分代表的群体的成员。酸度、水分、极性和组成的变化可能导致液-液分离，从而改变颗粒界面的性质。因此，气溶胶成分的变化可以改变颗粒的形态，进而改变进一步的气固反应的动力学和反应机理。包括液滴pH在内的一系列关键化学性质的演变将在粒子经历水相反应时确定，例如与两种重要的痕量气体：N2O5和异戊二烯氧化生成的环氧二醇IEPOX。要测定的物理化学性质包括相分离和形态、酸度和扩散系数，作为相对湿度(RH)、温度和液滴大小的函数。这项研究致力于解决有关大气颗粒物的化学演化如何影响颗粒物对空气质量、人类健康、生态系统、酸沉积、辐射强迫、云微物理和气候变化的广泛影响的悬而未决的问题。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Environmental Chemical Sciences (ECS) Program in the Chemistry Division, Ryan Sullivan at Carnegie Mellon University will study atmospheric aerosols utilizing optical tweezers. Aerosols are micron-sized liquid or solid particles suspended in the air. They have unique chemical properties and reactivity because of their high surface area-to-volume ratio. Atmospheric aerosols can act as chemical catalysts, accelerating chemical reactions and facilitating aqueous-phase chemistry that cannot occur in the gas-phase alone. The properties of the aerosol surfaces play an important role in controlling the chemical reactivity of aerosols and their many effects on atmospheric chemistry, air quality, health, cloud microphysics and climate. A tool called aerosol optical tweezers (AOT) will be used in this project to carry out experiments on levitated droplets to determine the evolution of various key chemical properties. Aerosol acidity is a critical chemical property that strongly influences the chemistry of the interface and chemical kinetics. The experiments are expected to produce new chemical understanding of variations in particle composition, acidity, and morphology, that change the reactivity of these complex particles. In addition to training graduate and undergraduate students, Dr. Sullivan will create and deploy hands-on experiments and curricular materials on environmental chemistry for grade 6-12 students in local public schools which serve significant numbers of members of underrepresented groups.Changes in acidity, water content, polarity, and composition can cause liquid–liquid phase separations that alter the properties at the interface of the particle. Thus, changes in aerosol composition can alter particle morphology which in turn can change the kinetics and reaction mechanisms of further gas–particle reactions. The evolution of a suite of key chemical properties including droplet pH will be determined as a particle undergoes aqueous reactions such as with two important trace gases: N2O5 and the epoxydiol IEPOX produced from isoprene oxidation. Physicochemical properties to be determined include phase separations and morphology, acidity, and diffusivity, as a function of relative humidity (RH), temperature, and droplet size. This research sets out to address outstanding questions regarding how the chemical evolution of atmospheric particles affects the extensive impacts of particulate matter on air quality, human health, ecosystems, acid deposition, radiative forcing, cloud microphysics, and climate change.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.