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异质过程进行实验室研究。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，对污染、气候和生物地球化学具有重大的全球影响。发生在粉尘上的非均相化学对大气中的颗粒化学和气相化学都有显著影响。2001年的ACE-Asia实地活动是第一个使用单粒子质谱仪分析尘埃化学成分的重大研究。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法（ATOFMS）对颗粒进行化学分析，以及化学电离质谱法（CIMS）分析气相物质。反应将在气溶胶流管中进行，并控制粒径、反应物浓度、湿度和反应时间。详细的表面表征将由爱荷华大学的研究人员使用传统的SEM/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/傅里叶变换红外光谱）来探测相同的过程。通过竞争动力学实验表征不同类型粉尘和海盐与气相前驱体的相对反应性，确定控制粉尘和海盐形成二次产物的因素的相对重要性。此外，该项目将研究由各种酸诱导形成的可溶物质的化学转化如何影响反应尘埃颗粒的CCN（云凝结核）势。热梯度CCN仪器将使用逆流虚拟冲击器与ATOFMS连接，分离并直接测量激活颗粒与未激活颗粒之间的化学差异。从实验室研究中获得的动力学信息将作为输入，用于改进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测量结果进行比较来进行测试。该模型将用于开发所研究的异质过程的机理图。这些信息将反过来用于帮助设计未来的实地活动，以探索这些实验室研究在现实世界条件下的发现。这些研究将有助于培养大气化学、分析化学和环境化学的研究生和本科生。该项目还将进一步发展单粒子质谱法的定量能力。

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.