Abstract. This article presents a study of long-range transported biomass burning aerosols (BBA) originated from the North American wildfires in September 2020. The BBA plumes presented in this study were in the troposphere and underwent 1–2 weeks aging before arriving at the observations site. A novel dataset 2α+3β+3δ+φ (α: extinction coefficient, β: backscatter coefficient, δ: particle linear depolarization ratio, PLDR, φ: fluorescence capacity) derived from lidar observations is provided for the characterization of long-range transported BBA. The fluorescence capacity describes the ability of aerosols in producing fluorescence when exposed to UV excitation. In the observations of BBA episode, plumes from different wildfire activities have been characterized. In the BBA plumes, we detected low PLDRs, i.e. lower than 0.03 at all wavelengths, as well as enhanced PLDRs (PLDR_355,532,1064 ≈ 0.15–0.18, 0.12–0.14, 0.01–0.02) with a similar spectral dependence that had been observed in the aged BBA plumes in the upper troposphere and lower stratosphere (Canadian smoke in 2017 and Australian smoke in 2019–2020). Obvious variations in Angström exponent (−0.3–1.5), lidar ratios (20–50 sr at 355 nm, 42–90 sr at 532 nm) and fluorescence capacity (1.0 × 10⁻⁴– 4.0 × 10⁻⁴) are also observed during the BBA episode. These variations are coupled with the variation of altitudes, water vapor content and wildfire events. It reflects that the properties of aged BBA particles are highly varied and depend on complex mechanisms, such as burning process and the aging process. The results also pointed out the inhomogeneity of the aging process in the BBA plumes, which means that particles in the core of the plume aged differently with those at the plume edge due to the impact of water vapor, temperatures, particle concentration and so on. These chemical and physical processes involved in BBA aging and how they could impact the particle properties are not yet well understood. In addition, our observations identified the ice crystals mixing with BBA particles, which indicates that BBA could act as ice nucleating particles (INP) at tropospheric conditions. The lidar fluorescence proves to be an efficient tool in studying the interaction of clouds and BBAs due to its high sensitivity. Recent studies claimed that aged BBA particles are more effective INPs than they were thought. As BBAs are becoming an important atmospheric aerosols with growing global wildfires, our observations could improve our characterization about aged BBA particles and the understanding of their importance in ice cloud formation.

中文翻译：

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远程传输的北美生物质燃烧羽流的表征：多波长 Mie-Raman-偏振-荧光激光雷达可以提供什么？

摘要。本文介绍了对源自 2020 年 9 月北美野火的远距离传输的生物质燃烧气溶胶 (BBA) 的研究。本研究中的 BBA 羽流位于对流层中，在到达观测地点之前经历了 1-2 周的老化. 提供了来自激光雷达观测的新数据集 2α+3β+3δ+φ（α：消光系数，β：背向散射系数，δ：粒子线性去极化率，PLDR，φ：荧光容量）用于表征远程传输的 BBA . 荧光能力描述了气溶胶在暴露于紫外线激发下时产生荧光的能力。在对 BBA 事件的观察中，已经表征了来自不同野火活动的羽流。在 BBA 羽流中，我们检测到低 PLDR，即在所有波长下都低于 0.03，_355,532,1064 ≈ 0.15–0.18, 0.12–0.14, 0.01–0.02) 与在对流层上层和平流层下层的老化 BBA 羽流中观察到的类似光谱依赖性（2017 年的加拿大烟雾和 2019 年的澳大利亚烟雾） . Angström 指数 (-0.3–1.5)、激光雷达比率（355 nm 下 20–50 sr，532 nm 下 42–90 sr）和荧光容量（1.0 × 10 ^-4 – 4.0 × 10 ^{-4）的明显变化}) 在 BBA 期间也被观察到。这些变化与海拔、水汽含量和野火事件的变化相结合。这反映了老化 BBA 颗粒的性质变化很大，并且取决于复杂的机制，如燃烧过程和老化过程。结果还指出了BBA羽流老化过程的不均匀性，这意味着由于水汽、温度、粒子浓度等的影响，羽流核心的粒子与羽流边缘的粒子老化不同。这些涉及 BBA 老化的化学和物理过程以及它们如何影响粒子特性尚不清楚。此外，我们的观察发现冰晶与 BBA 颗粒混合，这表明 BBA 在对流层条件下可以充当冰核粒子 (INP)。由于其高灵敏度，激光雷达荧光被证明是研究云和 BBA 相互作用的有效工具。最近的研究声称老化的 BBA 颗粒是比他们想象的更有效的 INP。随着全球野火不断增加，BBA 正成为一种重要的大气气溶胶，我们的观察可以改善我们对老化 BBA 粒子的表征以及对它们在冰云形成中的重要性的理解。