Absorption Cross Sections and Primary Quantum Yields for Several Aliphatic Aldehydes and Ketones of Atmospheric Interest

光解是对流层中醛和酮的主要汇，也是自由基的主要来源，而自由基是其他大气成分化学中重要的活性中间体，包括臭氧和导致酸雨形成的化合物。醛和酮的光解离和化学反应之间的竞争是控制对流层自由基浓度的重要因素。在对流层化学模型中，脂肪族醛和酮的吸收截面、光解量子产率和初级光解产物的不确定性是一个重要的误差来源。这项研究是对脂肪族醛和酮的光谱和光化学性质的系统研究。这些化合物在200-400 nm波长范围内的气相吸收光谱将在氮气/氧气混合气体中作为温度的函数进行测量，以确定它们在对流层条件下的吸收截面。还将测量水溶液中的吸收光谱，以确定这些化合物在大气液滴中的横截面。几种化合物的气相和水相光解的初级量子产率将作为光解波长、温度、醛或酮的分压和总压(气相测量)以及pH和溶解氧浓度(水相测量)的函数来确定。这项研究的结果将阐明脂肪醛和酮在对流层化学和光化学中的作用。

Photodissociation is the major sink for aldehydes and ketones in the troposphere and is a primary source of free radicals which are important reactive intermediates in the chemistry of other atmospheric constituents including ozone and compounds that contribute to the formation of acid rain. The competition between photodissociation and chemical reaction of aldehydes and ketones is an important factor controlling tropospheric free radical concentrations. Uncertainty in the absorption cross sections, quantum yields for photodissociation, and primary photolysis products for aliphatic aldehydes and ketones represents a significant source of error in models of tropospheric chemistry. The proposed research is a systematic study of the spectral and photochemical properties of aliphatic aldehydes and ketones. The gas phase absorption spectra of these compounds in the wavelength region 200-400 nm will be measured in nitrogen/oxygen gas mixtures as a function of temperature to determine their absorption cross sections under conditions found in the troposphere. Absorption spectra will also be measured in aqueous solution to determine the cross sections for these compounds in atmospheric droplets. The primary quantum yields for gas phase and aqueous phase photodissociation of several of the compounds will be determined as a function of photolysis wavelength, temperature, partial pressure of aldehyde or ketone and total pressure (for gas phase measurements), and pH and dissolved oxygen concentration (for aqueous phase measurements). The results from the research will clarify the role of aliphatic aldehydes and ketones in the chemistry and photochemistry of the troposphere.