The impact of water droplets on soils has recently been found to drive emissions of airborne soil organic particles (ASOP). The chemical composition of ASOP include macromolecules such as polysaccharides, tannins, and lignin (derived from degradation of plants and biological organisms), which determine light absorbing (brown carbon) particle properties. Optical properties of ASOP were inferred from the quantitative analysis of the electron energy-loss spectra acquired over individual particles using transmission electron microscopy. The optical constants of ASOP are compared with those measured for laboratory generated particles composed of Suwanee River Fulvic Acid (SRFA) reference material, which is used as a laboratory surrogate of ASOP. The chemical composition of the particles was analyzed using energy dispersive X-ray spectroscopy, electron energy-loss spectroscopy, and synchrotron-based scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy. ASOP and SRFA exhibit similar carbon composition, with minor differences in other elements present. When ASOP are heated to 350 °C their absorption increases as a result of pyrolysis and partial volatilization of semivolatile organic constituents. The retrieved refractive index (RI) at 532 nm of SRFA particles, ASOP, and heated ASOP were 1.22–0.07i, 1.29–0.07i, and 1.90–0.38i, respectively. Retrieved imaginary part of the refractive index of SRFA particles derived from EELS measurements was higher and the real part was lower compared to data from more common optical methods. Therefore, corrections to the EELS data are needed for incorporation into models. These measurements of ASOP optical constants confirm that they have properties characteristic of atmospheric brown carbon and therefore their potential effects on the radiative forcing of climate need to be assessed in atmospheric models.

中文翻译：

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空气中土壤有机颗粒的光学性质

最近发现水滴对土壤的影响会促使空气中的土壤有机颗粒（ASOP）排放。ASOP的化学成分包括大分子，例如多糖，单宁和木质素（来源于植物和生物的降解），它们决定了光吸收（棕碳）颗粒的特性。通过使用透射电子显微镜对单个颗粒上获得的电子能量损失谱进行定量分析，可以推断出ASOP的光学特性。将ASOP的光学常数与由Suwanee River富勒酸（SRFA）参考材料组成的实验室产生的颗粒测量的光学常数进行比较，该颗粒用作ASOP的实验室替代物。使用能量色散X射线光谱仪分析了颗粒的化学成分，电子能量损失光谱，以及基于同步加速器的扫描透射X射线显微镜和近边缘X射线吸收精细结构光谱。ASOP和SRFA表现出相似的碳组成，但存在的其他元素略有不同。当ASOP加热到350°C时，由于半挥发性有机成分的热解和部分挥发，它们的吸收增加。SRFA颗粒，ASOP和加热的ASOP在532 nm处的折光率（RI）分别为1.22-0.07i，1.29-0.07i和1.90-0.38i。与来自更常见的光学方法的数据相比，从EELS测量获得的SRFA粒子的折射率的虚部得到的虚高更高，而实部却更低。因此，需要对EELS数据进行校正才能将其合并到模型中。