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

93100470包括云和雾中水滴的Davidovits多相反应路径是对流层和平流层中大气痕量气体化学转化的重要通道。在过去的八年里，波士顿学院化学系和Aerodyne Research，Inc.的化学和环境物理中心在国家科学基金会的部分支持下，合作开发了两种新的和强大的技术，用于研究气体吸收过程和测量痕量大气物种在水和其他液体上的质量调节系数。这些技术还可以提供有关气液界面化学相互作用性质的信息。在第一种方法中，适用于测量相对较大的气体吸收，气相物种与已知大小、温度和化学成分的小(50至250微米半径)单分散液滴的可控流相互作用。还建造了一个使用硫酸液滴的这种装置的版本，用于研究温度低至-50摄氏度的平流层重要过程。在第二种方法中，用于研究吸收相对较小的气体，痕量气体被包含在通过感兴趣液体上升的受控气泡中。在过去的两个NSF支持期内，研究了在广泛的大气相关条件下，作为温度函数的30多种气相物种的吸收。所研究的物种包括SO2和还原硫化合物、H_2O_2、N_2O_5、HNO_3、HCl、ClNO_3和N_2O_5。这项工作提供了决定对流层和平流层重要物种吸收的参数的值，并导致了非反应气体吸收的定量模型的形成。此外，还注意到了气液界面化学相互作用的重要特征。在某些情况下，例如甲醛和光气，吸收与物种的主体水化学完全一致。但在其他情况下，如二氧化硫和乙醛的吸收，结果无法用主体相化学解释。相反，这些结果表明，气液界面上的反应是气相或液态的主要成分。界面上的反应可能比气相或液体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，在气液界面形成化学吸附的络合物，可能参与物种的非均相化学。这笔赠款中的工作计划将继续研究对大气具有重要意义的非均质过程。这项研究将包括对NO、NO2、N3、N2O5、HNO3、HONO、NH3、SO2、CH2O和OH的气体吸收和共沉积研究。实验将在水溶液、硫酸和亚硝基硫酸溶液中作为温度的函数进行。将考察光化学、表面电荷和各种与大气相关的添加剂对多相过程的影响。研究研究的两个主要目标是：(A)继续测量评估对对流层和平流层重要的物种的非均质化学所需的参数。B)对气液界面的化学有一个概括性的、预测性的了解。

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.