Formaldehyde Chemical Actinometer for the Troposphere: Measurements of Photolysis Rate Coefficient, H2 and H02 Branching Ratios, and Comparison with other Ultraviolet Ligh

9422307 海克斯 甲醛的光解是烃类在大气中氧化的重要中间步骤，并导致直接形成一氧化碳、氢和过羟基自由基。后两者是通过两种不同的光解途径产生的。过氧化氢通道对光化学净生成奇数氢、臭氧、过氧化氢和有机氢过氧化物具有重要意义。光解速率的不确定性和两个通道之间的分支直接导致大气氧化能力的不确定性。这些速率目前估计使用建模光化通量的光，实验室衍生的甲醛吸收截面，和实验室衍生的量子产率。大气中的气体、气溶胶和云干扰了光化通量的计算。这与实验室数据中的测量不确定性一起可能导致甲醛光解速率和光解产生的自由基速率的重大误差。 本计画将建构一化学光化仪，直接量测甲醛之光解速率及产物分布。还将测量环境甲醛浓度。这些测量结果将与理论模型结合使用，以测试我们对甲醛光解的理解，并评估其作为过羟基自由基来源的强度。测量的光解率和分支比将与窄带和宽带紫外线辐照度测量相关联。确定的相关性将允许使用更简单的辐照度测量来估计甲醛的光解性能。

9422307 Heikes The photolysis of formaldehyde is an important intermediate step in the atmospheric oxidation of hydrocarbons and leads to the direct formation of carbon monoxide, hydrogen, and perhydroxyl radicals. The later two are produced through two different photolysis channels. The perhydroxyl channel is significant to the net photochemical production of odd-hydrogen, ozone, hydrogen peroxide, and organic hydroperoxides. Uncertainties in the photolysis rate and in the branching between the two channels lead directly to uncertainties in the oxidizing power of the atmosphere. These rates are currently estimated using modeled actinic fluxes of light, laboratory derived formaldehyde absorption cross sections, and laboratory derived quantum yields. Atmospheric gases, aerosols, and clouds confound the actinic flux calculation. This together with measurement uncertainties in the laboratory data may lead to significant errors in the photolysis rates and radical production rates from the photolysis of formaldehyde. In this project, a chemical actinometer will be constructed to measure directly the photolysis rate of formaldehyde and the product distribution. Ambient formaldehyde concentrations will also be measured. These measurements will be used in conjunction with theoretical models to test our understanding of formaldehyde photolysis and evaluate its strength as a perhydroxyl radical source. Measured photolysis rates and branching ratios will be correlated with narrow-band and broad-band UV irradiance measurements. Correlations identified will permit the use of more simple irradiance measurements to estimate formaldehyde photolysis properties.