Abstract. Mixed-phase clouds (MPCs) are key players in the Arctic climate system due to their role in modulating solar and terrestrial radiation. Such radiative interactions rely, among other factors, on the ice content of MPCs, which is regulated by the availability of ice-nucleating particles (INPs). While it appears that INPs are associated with the presence of primary biological aerosol particles (PBAPs) in the Arctic, the nuances of the processes and patterns of INPs and their association with clouds and moisture sources have not been resolved. Here, we investigated for a full year the abundance of and variability in fluorescent PBAPs (fPBAPs) within cloud residuals, directly sampled by a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory (475 m a.s.l.) in Ny-Ålesund, Svalbard. fPBAP concentrations (10−3–10−2 L−1) and contributions to coarse-mode cloud residuals (0.1 to 1 in every 103 particles) were found to be close to those expected for high-temperature INPs. Transmission electron microscopy confirmed the presence of PBAPs, most likely bacteria, within one cloud residual sample. Seasonally, our results reveal an elevated presence of fPBAPs within cloud residuals in summer. Parallel water vapor isotope measurements point towards a link between summer clouds and regionally sourced air masses. Low-level MPCs were predominantly observed at the beginning and end of summer, and one explanation for their presence is the existence of high-temperature INPs. In this study, we present direct observational evidence that fPBAPs may play an important role in determining the phase of low-level Arctic clouds. These findings have potential implications for the future description of sources of ice nuclei given ongoing changes in the hydrological and biogeochemical cycles that will influence the PBAP flux in and towards the Arctic.

中文翻译：

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荧光初级生物气溶胶颗粒对北极低层云残留的贡献

摘要。混合相云（MPC）因其在调节太阳和陆地辐射方面的作用而成为北极气候系统的关键参与者。除其他因素外，这种辐射相互作用依赖于 MPC 的冰含量，而 MPC 的冰含量受冰成核粒子 (INP) 的可用性调节。虽然 INP 似乎与北极地区初级生物气溶胶颗粒 (PBAP) 的存在有关，但 INP 过程和模式的细微差别及其与云和水分源的关联尚未得到解决。在这里，我们研究了全年云残留中荧光 PBAP (fPBAP) 的丰度和变异性，通过与齐柏林天文台 (475 m asl) 的地面逆流虚拟撞击器入口耦合的多参数生物气溶胶光谱仪直接采样。新奥勒松，斯瓦尔巴特群岛。 fPBAP 浓度 (10−3–10−2 L−1) 和对粗模式云残差的贡献（每 103 个粒子 0.1 到 1 个）被发现接近高温 INP 的预期值。透射电子显微镜证实了云残留样品中存在 PBAP，很可能是细菌。从季节性来看，我们的结果显示夏季云残差中 fPBAP 的存在量有所增加。平行水蒸气同位素测量表明夏季云与区域来源的气团之间存在联系。低水平 MPC 主要在夏初和夏末观察到，其存在的一种解释是高温 INP 的存在。在这项研究中，我们提供了直接观测证据，表明 fPBAP 可能在确定北极低层云的相位方面发挥重要作用。鉴于水文和生物地球化学循环的持续变化将影响北极内部和流向北极的 PBAP 通量，这些发现对未来冰核来源的描述具有潜在影响。