Laboratory Studies of Heterogeneous Gas-Liquid Interaction of Atmospheric Trace Gases

小行星93100470 云雾中水滴的非均相反应路径是对流层和平流层大气痕量气体化学转化的重要通道。 在过去的八年里，在波士顿学院化学系和航空达因研究公司化学与环境物理中心的合作努力下，在国家科学基金会的部分支持下，已经开发了两种新颖而强大的技术，用于研究气体吸收过程和测量痕量大气物质在水和其他液体上的质量适应系数。 这些技术还可以产生关于气液界面处化学相互作用的性质的信息。 在第一种方法中，适用于测量相对较大的气体吸收，气相物质与已知尺寸、温度和化学组成的小（50至250 μ m半径）单分散液滴的可控流相互作用。 使用硫酸液滴的这种装置的一个版本也被建造出来，用于研究温度低至-50 ° C的平流层重要过程。 在第二种方法中，用于研究具有相对较小吸收的气体，痕量气体包含在通过感兴趣的液体上升的受控气泡中。 在过去的两个NSF的支持期间，超过30个气相物种的吸收已被研究作为温度的函数在大范围的大气相关条件。 所研究的物种包括SO2和还原硫化合物，H2 O2，N2 O 5，HNO 3，HCl，ClNO 3和N2 O 5。 这项工作提供了值的参数确定对流层和平流层的重要物种的吸收，它导致了非反应性气体的吸收的定量模型的形成。 此外，在气-液界面的化学相互作用的重要特征被注意到。 在某些情况下，如甲醛和光气，吸收是完全一致的物质的散装水化学。 但在其他情况下，如二氧化硫和乙醛的吸收，结果是无法解释的体相化学。 相反，这些结果表明，在气-液界面的反应占主导地位的气相或液相。 界面处的反应可能比气相或液相中的反应快几个数量级。 还观察到，在吸收过程中，一些物种，如SO2，在气-液界面处形成化学吸附复合物，这可能参与物种的非均相化学。 这项赠款的工作计划将继续进行对大气重要的异质过程的研究。 该研究将包括对NO、NO2、NO3、N2 O 5、HNO 3、HONO、NH3、SO2、CH 2 O和OH的气体吸收和共沉积研究。 实验将构建为水溶液、硫酸和亚硝酰硫酸溶液的温度函数。 将研究光化学、表面电荷和各种大气相关添加剂对非均相过程的影响。 研究的两个主要目标是： a）、 继续测量所需参数， 评估重要物种的异质化学 对流层和平流层。 B） 对…有一个普遍的、有预见性的了解 气液界面的化学反应。

93100470 Davidovits Heterogeneous reaction pathways involving aqueous droplets in clouds and fogs are important conduits for chemical transformation of atmospheric trace gases both in the troposphere and in the stratosphere. During the past eight years in a collaborative effort between the Chemistry Department at Boston College and the Center for Chemical and Environmental Physics at Aerodyne Research, Inc., supported in part by the National Science Foundation, two novel and powerful techniques have been developed for studying gas uptake processes and for measuring mass accommodation coefficients of trace atmospheric species on water and other liquids. These techniques can also yield information about the nature of chemical interactions at the gas-liquid interface. In the first method, suitable for measuring relatively large gas uptakes, the gas phase species interacts with a controllable stream of small (50 to 250 um radius) monodispered droplets of known size, temperature and chemical composition. A version of this apparatus using sulfuric acid droplets has also been built to study stratospherically important processes down to a temperature of -50oC. In the second method, used to study gases with relatively smaller uptakes, the trace gas is contained in controlled bubbles rising through the liquid of interest. During the past two NSF support periods the uptake of more than thirty gas phase species has been studied as a function of temperature over a wide range of atmospherically relevant conditions. The species studied include SO2 and reduced sulfur compounds, H2O2, N2O5, HNO3, HCl, ClNO3 and N2O5 the uptake by aqueous sulfuric acid droplets was also measured as a function of temperature down to -50oC. This work provided values for the parameters determining uptake for both tropospherically and stratospherically important species and it led to the formation of a quantitative model for the uptake of nonreactive gases. Further, important features of chemical interactions at the gas-liquid interface were noted. In some cases, such as formaldehyde and phosgene, the uptake was entirely consistent with the bulk aqueous chemistry of the species. But in other cases, such as the uptake of sulfur dioxide and acetaldehyde, results were not explainable by bulk phase chemistry. Instead, these results indicate that reactions at the gas-liquid interface dominate the gas or the liquid phase. Reactions may be orders of magnitude faster at the interface than either in the gas or in the liquid phases. It was also observed, that in the process of uptake, some species such as SO2, form a chemisorbed complex at the gas-liquid interface which is likely to participate in the heterogeneous chemistry of the species. The work plan in this grant will continue to pursue the study of atmospherically important heterogeneous processes. The research will include gas uptake and co-deposition studies for NO, NO2, NO3, N2O5, HNO3, HONO, NH3, SO2, CH2O and OH. Experiments will be constructed as a function of temperature with aqueous solutions, with sulfuric acid and with nitrosyl sulfuric acid solutions. The effect on heterogeneous processes of photochemistry, surface charge and various atmospherically relevant additives will be examined. The two major objectives of the research studies are: a) To continue the measurement of parameters required to assess the heterogeneous chemistry of species important to troposphere an stratosphere. b) To obtain a general, predictive understanding of chemistry at the gas-liquid interface.