Sensitivity and accuracy of refractive index retrievals from measured extinction and absorption cross sections for mobility-selected internally mixed light absorbing aerosols
Sensitivity and accuracy of refractive index retrievals from measured extinction and absorption cross sections for mobility-selected internally mixed light absorbing aerosols
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DOI：
10.1080/02786826.2020.1757034
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发表时间：
2020-05-20
影响因子：
5.2
通讯作者：
Langridge, Justin M.
中科院分区：
文献类型：
--
作者：
Cotterell, Michael I.;Szpek, Kate;Langridge, Justin M.
气溶胶折射率（RI）与粒子的组成和密度有关，在光谱学研究中用于探测化学反应和气-粒分离过程中气溶胶的物理化学性质，在大气物理学中也很重要。实际上，气溶胶辐射强迫计算需要精确描述真实的（n）和虚的（k）RI分量及其对波长、湿度和粒子混合状态的依赖性。利用光腔衰荡光谱（CRDS）和光声光谱（PAS）测量迁移率选择气溶胶的消光截面和吸收截面被认为是精确反演n和k的一种很好的方法。然而，很少有工作严格评估的敏感性和准确性的检索值从这种方法。这项工作调查RI检索CRDS和PAS测量的光学性质的流动性选择的气溶胶组成的硫酸铵（非吸收），苯胺黑（强烈的光吸收）或这两个物种的混合物。重要的是，我们评估我们的RI检索的灵敏度，然后应用蒙特卡罗误差传播分析，以量化检索的准确性。我们的蒙特卡罗分析是第一个考虑到全方位的不确定性RI检索从光学测量的流动性选择的气溶胶。我们还报告了第一次实验验证的预测RI混合规则的非水内部混合光吸收气溶胶的混合规则预测与测量组成的内部混合物的硫酸铵和苯胺黑气溶胶。常用的体积分数混合规则不能准确地预测折射率，必须使用具有物理基础的混合规则。
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.