Atmosperic and interfacial reaction dynamics

暴露在大气中的表面控制着许多关键的大气过程，如雪和海面上卤化物的活化，氮氧化物化合物的损失，有机涂层对非均相水化学的抑制，以及沉积在城市表面的硝酸盐的光化学循环。我们研究计划的一个首要主题是将各种大气表面的化学形态与多相反应性联系起来。这项工作将建立在我们在过去取得的进展的基础上，并将引入一些新的工具。我们将集中在液体和冷冻的水体系上。(1)我们将探讨天然有机物在海水中观察到的溶液光化学差异是否表现为海面上不同的界面光化学。掠射角激光诱导荧光方法将测量样品在淡水和海水表面的吸附等温线，在没有和存在人造表面微层的情况下，以确定它们在空气-水边界作为光敏剂的有效性。与里昂小组合作，我们将使用PTR-MS测量含有这些化合物的照明淡水和海水样品中的气相有机化合物排放。我们将通过NO与R-O2的反应推断吸附在水面上的有机自由基的产生。这些实验将提供有关海水和淡水表面大气氧化剂和自由基的形成和化学反应差异的关键数据。(2)我们将利用量子化学和分子动力学手段来理解硝酸盐和硫酸盐阴离子在水溶液冻结过程中排斥行为不同的原因(S)。我们将把不同的拉曼探针与气相氮氧化物检测相结合，以将冷冻溶液中硝酸盐的溶剂化状态和特定位置与其光反应性联系起来。将使用同步加速器源(加拿大光源或瑞士保罗谢勒研究所)的X射线光束线启动新的实验，以确定硝酸盐与其他离子在空气界面上的位置是否与冰基质内的不同。(3)我们将实时监测水滴内的非均质大气化学。我们打算：(A)充分探索与蒸发有机-无机混合液滴相关的形态变化，以了解相关的过程。(B)进一步开发光谱探测器，以测量液滴内的非均相动力学。具体地说，我们将使用液滴中的吸收和拉曼探测(以监测pH值和成分)和周围空气中的气相NOx测量来探索界面传输过程中二氧化氮和二氧化碳对有机涂层不同响应的原因(S)。(C)使用基于激光的拉曼和荧光探针来询问液滴整体区域和近表面区域的成分(和动力学)差异。

Surfaces exposed to the atmosphere control many key atmospheric processes, such as activation of halides at snow and sea surfaces, loss of nitrogen oxide compounds, inhibition of heterogeneous aqueous chemistry by organic coatings and photochemical recycling of nitrates deposited on urban surfaces. An overarching theme of our research program is to relate the chemical morphology of various atmospheric surfaces to  heterogeneous reactivity. This work will build on the advances we have made during the past and will introduce some new tools as well. We will concentrate on aqueous systems, both liquid and frozen. (1) We will explore whether differences in solution photochemistry observed for natural organic material in seawater manifest as different interfacial photochemistry at sea surfaces. Glancing-angle LIF methods will measure adsorption isotherms for the samples at the freshwater and seawater surfaces, in the absence and presence of an artificial surface microlayer, to establish how effectively they may act as photosensitizers at the air-water boundary. In collaboration with the Lyon group, we will use PTR-MS to measure gas phase organic compound emission from illuminated freshwater and seawater samples containing these compounds. We will infer the production of organic radicals adsorbed at the water surface via the reaction of NO with R-O2. These experiments will provide key data concerning differences in the formation and chemical reactions of atmospheric oxidants and radicals at seawater and freshwater surfaces. (2) We will use quantum chemical and molecular dynamics tools to understand the reason(s) for the differences between the exclusion behaviors of nitrate and sulfate anions during freezing of aqueous solutions. We will combine different Raman probes with gas phase nitrogen oxide detection to relate the solvation state and specific location of the nitrate in frozen solutions to its photoreactivity. New experiments will be initiated using an x-ray beamline of a synchrotron source (at the Canadian Light Source or at the Paul Sherer Institute in Switzerland) to determine whether nitrate is co-located with other ions differently at the air interface than within the ice matrix. (3) We will monitor heterogeneous atmospheric chemistry within droplets, in real time. We intend to: (a) fully explore the morphology changes associated with evaporating mixed organic-inorganic drops, to understand the processes responsible. (b) Further develop spectroscopic probes to measure heterogeneous kinetics within droplets. Specifically, we will use absorption and Raman probing within the droplets (to monitor pH and composition) and gas phase NOx measurements in the surrounding air to explore the reason(s) for the different responses of NO2 and CO2 to organic coatings during interfacial transport. (c) Use laser-based Raman and fluorescence probes to interrogate composition (and kinetics) differences in the bulk vs. near-surface regions of the droplet.