Ice-nucleating particles (INPs) initiate the primary ice formation in clouds at temperatures above ca. −38 ^∘C and have an impact on precipitation formation, cloud optical properties, and cloud persistence. Despite their roles in both weather and climate, INPs are not well characterized, especially in remote regions such as the Arctic. We present results from a ship-based campaign to the European Arctic during May to July 2017. We deployed a filter sampler and a continuous-flow diffusion chamber for offline and online INP analyses, respectively. We also investigated the ice nucleation properties of samples from different environmental compartments, i.e., the sea surface microlayer (SML), the bulk seawater (BSW), and fog water. Concentrations of INPs (N_INP) in the air vary between 2 to 3 orders of magnitudes at any particular temperature and are, except for the temperatures above −10 ^∘C and below −32 ^∘C, lower than in midlatitudes. In these temperature ranges, INP concentrations are the same or even higher than in the midlatitudes. By heating of the filter samples to 95 ^∘C for 1 h, we found a significant reduction in ice nucleation activity, i.e., indications that the INPs active at warmer temperatures are biogenic. At colder temperatures the INP population was likely dominated by mineral dust. The SML was found to be enriched in INPs compared to the BSW in almost all samples. The enrichment factor (EF) varied mostly between 1 and 10, but EFs as high as 94.97 were also observed. Filtration of the seawater samples with 0.2 µm syringe filters led to a significant reduction in ice activity, indicating the INPs are larger and/or are associated with particles larger than 0.2 µm. A closure study showed that aerosolization of SML and/or seawater alone cannot explain the observed airborne N_INP unless significant enrichment of INP by a factor of 10⁵ takes place during the transfer from the ocean surface to the atmosphere. In the fog water samples with −3.47 ^∘C, we observed the highest freezing onset of any sample. A closure study connecting N_INP in fog water and the ambient N_INP derived from the filter samples shows good agreement of the concentrations in both compartments, which indicates that INPs in the air are likely all activated into fog droplets during fog events. In a case study, we considered a situation during which the ship was located in the marginal sea ice zone and N_INP levels in air and the SML were highest in the temperature range above −10 ^∘C. Chlorophyll a measurements by satellite remote sensing point towards the waters in the investigated region being biologically active. Similar slopes in the temperature spectra suggested a connection between the INP populations in the SML and the air. Air mass history had no influence on the observed airborne INP population. Therefore, we conclude that during the case study collected airborne INPs originated from a local biogenic probably marine source.

中文翻译：

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陆地或海洋——欧洲北极地区高达 83.7° N 的融化季节期间冰核颗粒起源的迹象

冰成核粒子 (INPs) 在温度高于约 −38  ^∘ C，并对降水形成、云光学特性和云持久性产生影响。尽管它们在天气和气候中都发挥着作用，但 INP 并未得到很好的表征，尤其是在北极等偏远地区。我们展示了 2017 年 5 月至 7 月期间在欧洲北极进行的舰载运动的结果。我们分别部署了一个过滤采样器和一个连续流扩散室，用于离线和在线 INP 分析。我们还研究了来自不同环境区室的样品的冰成核特性，即海面微层 (SML)、大量海水 (BSW) 和雾水。_{INP 的}浓度 ( N _INP) 在任何特定温度下，空气中的 ) 在 2 到 3 个数量级之间变化，并且除了高于-10  ^∘ C 和低于-32  ^∘ C 的温度外，都低于中纬度地区。在这些温度范围内，INP 浓度与中纬度地区相同甚至更高。通过将过滤器样品加热到 95  ^∘C 1 小时，我们发现冰成核活性显着降低，即表明在较高温度下有活性的 INP 是生物源的。在较冷的温度下，INP 种群可能以矿物粉尘为主。与几乎所有样品中的 BSW 相比，发现 SML 富含 INP。富集因子 (EF) 主要在 1 到 10 之间变化，但也观察到高达 94.97 的 EF。用0.2的海水样品的过滤 μ导致冰活性的显著减少米注射器过滤器，指示所述综合邻舍是较大和/或与大于0.2的颗粒相关的 μ米。一项封闭研究表明，仅 SML 和/或海水的气溶胶化不能解释观察到的空气传播N _INP除非在从海洋表面转移到大气的过程中发生10 ⁵倍的显着 INP 富集。在-3.47  ^∘ C的雾水样品中，我们观察到任何样品的最高冻结开始。的封闭研究连接Ñ _INP雾水和周围Ñ _INP从在两个隔室中的浓度的过滤器样品显示良好的一致性，这表明在空气综合邻舍很可能所有期间雾事件活化成雾滴的。在案例研究中，我们考虑了船舶位于边缘海冰区和N _{INP 的情况}空气和 SML 中的水平在-10  ^∘ C以上的温度范围内最高。卫星遥感测量的叶绿素 a指向研究区域中具有生物活性的水域。温度谱中的类似斜率表明 SML 中的 INP 种群与空气之间存在联系。气团历史对观察到的空气传播 INP 人口没有影响。因此，我们 得出的结论是，在案例研究期间收集的空气中 INP 源自当地的生物源可能是海洋来源。