Free Radical Kinetics Important in Atmospheric Aerosols

将在实验室中测量液相中自由基反应的速率常数，以确定离子强度、pH值和几个重要反应系统在与大气相关的一系列变量上对温度的依赖性。早期的测量没有延伸到大气气溶胶中可能发生的非常高的电解质浓度。这项工作的重点将是硝酸根与卤素物种的反应，这是重要的理解“卤素活化”。这是一个知之甚少的过程，通过该过程，溶解在气溶胶中的卤化物被氧化以产生光化学活性的气相含卤素物质。它们可以被阳光光解并产生游离的卤素原子，这些卤素原子攻击气相臭氧和其他痕量大气成分。这些过程与北极地区极地日出后不久观测到的对流层臭氧消耗事件有关。水相中的自由基反应通过前体的光解离和气相自由基的溶剂化而引发。将使用激光闪光光解/时间分辨吸收法进行测量。控制实验条件以隔离离子强度、pH、温度和任何其他所需变量的影响。由此得到的速率常数可直接用于大气模式。

Rate constants for free radical reactions in the liquid phase will be measured in the laboratory to determine the ionic strength, pH, and temperature dependence of several important reaction systems over a range of variables relevant to the atmosphere. Earlier measurements do not extend to the very high electrolyte concentrations that can occur in atmospheric aerosols. The focus of this work will be on the reactions of the nitrate radical with halogen species which are important to understand "halogen activation". This is a poorly understood process by which halides dissolved in aerosols are oxidized to yield photochemically active gas phase halogen-containing species. These can be photolyzed by sunlight and produce free halogen atoms, which attack gas phase ozone and other trace atmospheric constituents. These processes have been implicated in observed tropospheric ozone depletion events shortly after polar sunrise in the Arctic. Free radical reactions in the aqueous phase are initiated by photodissociation of precursors and by the solvation of gas phase free radicals. The measurements will be performed by using the laser flash photolysis/time-resolved absorption method. The experimental conditions are controlled in order to isolate the effects of ionic strength, pH, temperature, and any other variables desired. The rate constants which result from this work can be used directly in atmospheric models.