Aerosols generated from aqueous samples of readily obtainable humic material standards are often used as proxies for organic particulates found in the atmosphere in various investigations, such as consideration of radiative forcing effects. Here, we present results for the retrieved complex index of refraction, m = n + ik, at a wavelength of 403 nm for aerosols prepared from six humic material standards using a calibrated cavity ring-down spectrometer: a humic acid sodium salt, Pahokee peat humic and fulvic acids, Elliott soil humic and fulvic acids, and Suwannee river fulvic acid. In addition, we have conducted UV–vis spectrometric studies to measure the mass absorption coefficients, molar absorptivities, and absorption Ångstrom exponents of bulk aqueous solutions of the humic materials. We find clear differences between the humic acid (HA) and fulvic acid (FA) samples with the HA having larger values for the imaginary part of the refractive index, k. The mean value for the HA samples is k = 0.170 while the mean is k = 0.037 for the FA materials. We have examined correlations between the retrieved refractive index and humic material characteristics obtained from spectroscopic and elemental analysis, including aromatic content and the oxygen-to-carbon atomic ratio, where the molar absorption coefficient yields the strongest correlation. Finally, we compare the humic material optical properties to those of authentic and laboratory generated organic carbon samples in order to assess the usefulness of these humic standards as proxies for light absorbing aerosol.

中文翻译：

---

腐殖质标准品的光学性质：溶液相和气溶胶测量

从容易获得的腐殖质材料标准品的水性样品中产生的气溶胶经常被用作各种研究中大气中发现的有机微粒的代理，例如考虑辐射强迫效应。在这里，我们给出检索到的复折射率m = n + ik的结果对于使用六种腐殖质标准品使用校准腔衰荡光谱仪制备的气溶胶，波长为403 nm：腐殖酸钠盐，Pahokee泥炭腐殖酸和富里酸，Elliott土壤腐殖酸和富里酸以及Suwannee河富黄酸。此外，我们已经进行了紫外可见光谱研究，以测量腐殖质材料大体积水溶液的质量吸收系数，摩尔吸收率和吸收埃数。我们发现，腐殖酸（HA）和黄腐酸（FA）样品之间存在明显差异，其中HA对于折射率k的虚部具有较大的值。对于HA样品的平均值是ķ = 0.170而平均是ķ= 0.037（对于FA材料）。我们检查了通过光谱和元素分析获得的折射率与腐殖质特性之间的相关性，包括芳香族含量和氧碳原子比，其中摩尔吸收系数产生了最强的相关性。最后，我们将腐殖质材料的光学性能与真实的和实验室产生的有机碳样品进行比较，以评估这些腐殖质标准作为吸光气溶胶的代理的有用性。