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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Infrared Optical Constants of Highly Diluted Sulfuric Acid Solution Droplets at Cirrus Temperatures
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Infrared Optical Constants of Highly Diluted Sulfuric Acid Solution Droplets at Cirrus Temperatures

机译：卷云温度下高度稀释的硫酸溶液液滴的红外光学常数

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摘要

Complex refractive indices for supercooled sulfuric acid solution droplets in the mid-infrared spectral regime (wavenumber range 6000—800 cm~(-1)) have been retrieved for acid concentrations ranging from 33 to 10 wt % H2SO4 at temperatures between 235 and 230 K, from 36 to 15 wt % H2SO4 at temperatures between 225 and 219 K, and from 37 to 20 wt % H2SO4 at temperatures between 211 and 205 K. The optical constants were derived with a Mie inversion technique from measured H2SO4/H2O aerosol extinction spectra that were recorded during controlled expansion cooling experiments in the large coolable aerosol chamber AIDA of Forschungszentrum Karlsruhe. The new data sets cover a range of atmospherically relevant temperatures and compositions in the binary sulfuric acid/water system for which infrared refractive indices have not been published so far, namely, the regime when supercooled H2SO4/H2O solution droplets at T < 235 K are subjected to an environment that is supersaturated with respect to the ice phase. With increasing ice supersaturation, the H2SO4/H2O aerosol particles will continuously dilute by the uptake of water vapor from the gas phase until freezing of the solution droplets eventually occurs when the acid concentration has dropped below a critical, temperature-dependent threshold value. With the aid of the new measurements, the homogeneous freezing process of supercooled H2SO4/H2O solution droplets at cirrus temperatures can be quantitatively analyzed by means of Fourier transform infrared spectroscopy, thereby overcoming a major drawback from previous studies: the need to use complex refractive indices that were measured at temperatures well above 235 K to deduce the composition of the low-concentrated H2SO4/H2O aerosol particles. As in the case of the complex refractive indices for sulfuric acid solutions with acid concentrations greater than 37 wt % H2SO4, the new low-temperature optical constants for highly diluted droplets also reveal significant temperature-induced spectral variations in comparison with the refractive indices for higher temperatures, which are associated with a change in the equilibrium between sulfate and bisulfate ions.
机译：在235至230 K之间的温度下，对于酸浓度范围为33至10 wt％的H2SO4，已经获得了中红外光谱范围（波数范围6000-800 cm〜（-1））中过冷硫酸溶液液滴的复数折射率。在225至219 K之间的温度下为36至15 wt％的H2SO4，在211至205 K之间的温度下为37至20 wt％的H2SO4。使用Mie反演技术从测得的H2SO4 / H2O气溶胶消光光谱得出光学常数在Forschungszentrum Karlsruhe的大型可冷却气雾室AIDA中的受控膨胀冷却实验中记录了这些数据。新的数据集涵盖了到目前为止尚未公布红外折射率的二元硫酸/水系统中与大气有关的温度和成分范围，即在T <235 K时过冷的H2SO4 / H2O溶液液滴为处于相对于冰相过饱和的环境。随着冰过饱和度的增加，H2SO4 / H2O气溶胶颗粒将被气相中的水蒸气吸收而不断稀释，直到当酸浓度降至低于临界值的温度相关阈值时最终发生溶液液滴冻结为止。借助新的测量方法，可以通过傅立叶变换红外光谱法对卷云温度下的过冷H2SO4 / H2O溶液液滴的均匀冷冻过程进行定量分析，从而克服了以前研究的主要缺点：使用复折射率在远高于235 K的温度下进行了测量，得出了低浓度的H2SO4 / H2O气溶胶颗粒的组成。与酸浓度大于37 wt％H2SO4的硫酸溶液的复数折射率相同，与较高的折射率相比，高度稀释的液滴的新的低温光学常数也显示出明显的温度引起的光谱变化。温度，这与硫酸根和硫酸氢根离子之间的平衡变化有关。

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