Abstract. Light-absorbing organic matter, known as brown carbon (BrC), has previously been found to significantly enhance the absorption of solar radiation by biomass burning (BB) aerosol. Previous studies also proposed methods aimed at constraining the BrC contribution to the overall aerosol absorption using the absorption Ångström exponents (AAEs) derived from the multi-wavelength remote observations at Aerosol Robotic Network (AERONET). However, representations of the BrC absorption in atmospheric models remain uncertain, particularly due to the high variability of the absorption properties of BB organic aerosol (OA). As a result, there is a need for stronger observational constraints on these properties. We extend the concept of the established AAE-based methods in the framework of our Bayesian method, which combines remote optical observations with Monte Carlo simulations of the aerosol absorption properties. We propose that the observational constraints on the absorption properties of BB OA can be enhanced by using the single scattering albedo (SSA) as part of the observation vector. The capabilities of our method were first examined by using synthetic data, which were intended to represent the absorption properties of BB aerosol originating from wildfires in Siberia. We found that observations of AAEs and SSA can provide efficient constraints not only on the BrC contribution to the total absorption but also on both the imaginary part of the refractive index and mass absorption efficiency of OA. As a result of the subsequent application of our method to the original multi-annual data from Siberian AERONET sites, we estimated that the average contribution of BrC to the overall light absorption by BB aerosol in Siberia at the 440 nm wavelength is about 15 %, although, in some cases, it can be more than 30 %. Based on the analysis of the AERONET data, we also derived simple nonlinear parameterizations for the absorption characteristics of BB OA in Siberia as functions of AAE.

中文翻译：

---

从远程光学观测推断生物质燃烧羽流中有机气溶胶的吸收特性

摘要。先前已发现，称为褐碳 (BrC) 的吸光有机物可显着增强生物质燃烧 (BB) 气溶胶对太阳辐射的吸收。先前的研究还提出了旨在使用来自气溶胶机器人网络 (AERONET) 的多波长远程观测的吸收 Ångström 指数 (AAE) 来限制 BrC 对整体气溶胶吸收的贡献的方法。然而，大气模型中 BrC 吸收的表示仍然不确定，特别是由于 BB 有机气溶胶 (OA) 吸收特性的高度可变性。因此，需要对这些属性进行更强的观察约束。我们在贝叶斯方法的框架中扩展了已建立的基于 AAE 的方法的概念，它将远程光学观测与气溶胶吸收特性的蒙特卡罗模拟相结合。我们建议可以通过使用单散射反照率 (SSA) 作为观测向量的一部分来增强对 BB OA 吸收特性的观测约束。我们的方法的能力首先通过使用合成数据进行了检查，这些数据旨在代表源自西伯利亚野火的 BB 气溶胶的吸收特性。我们发现，对 AAE 和 SSA 的观察不仅可以有效地限制 BrC 对总吸收的贡献，而且可以有效地限制 OA 的折射率的虚部和质量吸收效率。由于随后将我们的方法应用于来自西伯利亚 AERONET 站点的原始多年数据，我们估计 BrC 对西伯利亚 BB 气溶胶在 440 nm 波长的整体光吸收的平均贡献约为 15%，尽管在某些情况下，它可能超过 30%。基于对 AERONET 数据的分析，我们还导出了作为 AAE 函数的西伯利亚 BB OA 吸收特性的简单非线性参数化。