Abstract Aerosol refractive index (RI) is related to particle composition and density, is used in optical spectroscopy studies to probe aerosol physiochemical properties during chemical reactions and gas-particle partitioning, and is important in atmospheric physics. Indeed, aerosol radiative forcing calculations require accurate descriptions of the real (n) and imaginary (k) RI components and their dependence on wavelength, humidity and particle mixing state. Using cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS) to measure the extinction and absorption cross sections for mobility-selected aerosols is recognized as a good approach to retrieving n and k accurately. However, little work has assessed rigorously the sensitivity and accuracy of the retrieved values from this approach. This work investigates RI retrievals from CRDS- and PAS-measured optical properties for mobility-selected aerosols composed of ammonium sulfate (non-absorbing), nigrosin (strongly light absorbing) or a mixture of these two species. Importantly, we assess the sensitivity in our RI retrievals and then apply a Monte Carlo error propagation analysis to quantify the retrieval accuracy. Our Monte Carlo analysis is the first to account for the full range of uncertainties involved in RI retrievals from optical measurements on mobility-selected aerosol. We also report the first experimental validation of predictive RI mixing rules for non-aqueous internally mixed light absorbing aerosols by comparing mixing rule predictions with measurements for aerosol composed of internal mixtures of ammonium sulfate and nigrosin. The commonplace volume fraction mixing rule fails to predict refractive indices accurately and mixing rules with a physical basis must be used.

中文翻译：

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从流动性选择的内部混合吸光气溶胶的消光和吸收截面测量的折射率反演的灵敏度和准确性

摘要 气溶胶折射率 (RI) 与粒子组成和密度有关，在光谱学研究中用于探测化学反应和气体粒子分配过程中的气溶胶理化性质，在大气物理学中具有重要意义。实际上，气溶胶辐射强迫计算需要准确描述实部 (n) 和虚部 (k) RI 分量及其对波长、湿度和粒子混合状态的依赖性。使用腔衰荡光谱 (CRDS) 和光声光谱 (PAS) 测量迁移率选择的气溶胶的消光和吸收截面被认为是准确检索 n 和 k 的好方法。然而，很少有工作严格评估从这种方法中检索到的值的敏感性和准确性。这项工作研究了从 CRDS 和 PAS 测量的光学特性中对由硫酸铵（非吸收性）、苯胺黑（强光吸收性）或这两种物质的混合物组成的流动性选择气溶胶的 RI 反演。重要的是，我们评估了 RI 检索的敏感性，然后应用蒙特卡罗误差传播分析来量化检索准确性。我们的蒙特卡罗分析是第一个考虑了从流动性选择的气溶胶的光学测量中进行 RI 反演所涉及的所有不确定性的分析。我们还通过将混合规则预测与由硫酸铵和苯胺黑的内部混合物组成的气溶胶的测量值进行比较，报告了对非水性内部混合吸光气溶胶的预测 RI 混合规则的首次实验验证。