Collaborative Research: Field, Laboratory, and Modeling Investigations of Heterogeneous Processing of Asian Dust

该项目涉及对大气中尘埃颗粒发生的不同过程的实验室研究。尘埃占对流层粒子质量负担的一半以上。它可以跨大陆运输，并对污染、气候和生物地球化学产生重大的全球影响。尘埃上发生的非均相化学对大气中的颗粒和气相化学都有重大影响。2001年的ACE-Asia野外活动是第一项使用单粒子质谱仪分析尘埃化学的重大研究。这些观察结果为计划中的实验室动力学研究提供了灵感，该研究还将使用气溶胶飞行时间质谱仪(ATOFMS)对颗粒进行化学分析，并使用化学电离质谱仪(CIMS)分析气相物种。反应将在气溶胶流动管中进行，控制颗粒大小、反应物浓度、湿度和反应时间。爱荷华州大学的研究人员将使用传统的扫描电子显微镜/EDX(扫描电子显微镜/能量色散X射线分析)、XPS(X射线光电子能谱)和ATR-FTIR(衰减全反射/傅立叶变换红外光谱)来进行详细的表面表征，以探索相同的过程。将进行竞争性动力学实验，以表征不同类型的粉尘和海盐与气相前体的相对反应性，并确定控制二次产物形成的因素对粉尘和海盐的相对重要性。此外，该项目将研究由各种酸引起的形成可溶物质的化学转化如何影响反应的尘埃颗粒的CCN(云凝结核)电位。一台热梯度CCN仪器将使用逆流虚拟撞击器与ATOFMS对接，以分离并直接测量被激活的粒子与未被激活的粒子之间的化学差异。从实验室研究中获得的动力学信息将被用作输入，以完善爱荷华大学正在开发的区域化学模型，并通过将新输出与ACE-Asia的测量结果进行比较来进行测试。该模型将被用来开发所研究的非均质过程的机理图。这些信息反过来将被用来帮助设计未来的实地活动，以探索在现实世界条件下这些实验室研究的结果。这些研究将有助于培养大气、分析和环境化学方面的研究生和本科生。该项目还将进一步发展单粒子质谱学方法的定量能力。

This project involves laboratory studies of heterogeneous processes occurring on dust particles in the atmosphere. Dust represents over one half the tropospheric particle mass burden. It can be transported over trans-continental distances and has a major global impact on pollution, climate, and biogeochemistry. Heterogeneous chemistry occurring on dust significantly impacts both particle and gas phase chemistry in the atmosphere.The ACE-Asia field campaign in 2001 was the first major study that employed the use of a single particle mass spectrometer to analyze dust chemistry. These observations serve as the inspiration for the planned laboratory kinetics studies, which will also use aerosol time-of-flight mass spectrometry (ATOFMS) for chemical analysis of the particles, along with chemical ionization mass spectrometry (CIMS) to analyze gas phase species. The reactions will occur in an aerosol flow tube with controlled particle size, reactant concentration, humidity, and reaction time. Detailed surface characterization will be performed by U. of Iowa researchers using traditional SEM/EDX (Scanning Electron Microscopy/Energy-Dispersive X-ray analysis), XPS (X-Ray Photoelectron Spectroscopy), and ATR-FTIR (Attenuated Total Reflectance/Fourier-Transform Infra Red Spectroscopy) to probe the same processes. Competitive kinetics experiments will be carried out to characterize the relative reactivity of different types of dust and sea salt with gas phase precursors, and to determine the relative importance of the factors controlling secondary product formation on dust and sea salt. In addition, the project will examine how chemical transformations induced by various acids to form soluble species affect the CCN (cloud-condensation nuclei) potential of the reacted dust particles. A thermal gradient CCN instrument will be interfaced to an ATOFMS using a counterflow virtual impactor to separate and directly measure the chemical differences between those particles that activate versus those that do not.The kinetic information obtained from the laboratory studies will be used as input to refine regional chemistry models being developed at U. of Iowa and tested by comparing the new outputs to ACE-Asia measurements. The model will be used to develop a mechanistic picture of the heterogeneous processes studied. This information will in turn be used to help design future field campaigns to probe the findings of these lab studies under real world conditions. These studies will contribute to the training of graduate and undergraduate students in atmospheric, analytical, and environmental chemistry. The project will also further develop the quantitative abilities of single-particle mass spectrometry methods.