Abstract. New particle formation (NPF), referring to the nucleation of molecular clusters and their subsequent growth into the cloud condensation nuclei (CCN) size range, is a globally significant and climate-relevant source of atmospheric aerosols. Classical NPF exhibiting continuous growth from a few nanometers to the Aitken mode around 60–70 nm is widely observed in the planetary boundary layer (PBL) around the world, but not in central Amazonia. Here, classical NPF events are rarely observed in the PBL, but instead, NPF begins in the upper troposphere (UT), followed by downdraft injection of sub-50 nm (CN_< 50) particles into the PBL and their subsequent growth. Central aspects of our understanding of these processes in the Amazon have remained enigmatic, however. Based on more than six years of aerosol and meteorological data from the Amazon Tall Tower Observatory (ATTO, Feb 2014 to Sep 2020), we analyzed the diurnal and seasonal patterns as well as meteorological conditions during 254 of such Amazonian growth events on 217 event days, which show a sudden occurrence of particles between 10 and 50 nm in the PBL, followed by their growth to CCN sizes. The occurrence of events was significantly higher during the wet season, with 88 % of all events from January to June, than during the dry season, with 12 % from July to December, probably due to differences in the condensation sink (CS), atmospheric aerosol load, and meteorological conditions. Across all events, a median growth rate (GR) of 5.2 nm h⁻¹ and a median CS of 0.0011 s⁻¹ were observed. The growth events were more frequent during the daytime (74 %) and showed higher GR (5.9 nm h⁻¹) compared to nighttime events (4.0 nm h⁻¹), emphasizing the role of photochemistry and PBL evolution in particle growth. About 70 % of the events showed a negative anomaly of the equivalent potential temperature (∆θ'_e) – as a marker for downdrafts – and a low satellite brightness temperature (Tir) – as a marker for deep convective clouds – in good agreement with particle injection from the UT in the course of strong convective activity. About 30 % of the events, however, occurred in the absence of deep convection, partly under clear sky conditions, and with a positive ∆θ'_e anomaly. Therefore, these events do not appear to be related to downdraft injection and suggest the existence of other currently unknown sources of the sub-50 nm particles.

中文翻译：

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亚马逊边界层中亚 50 nm 气溶胶颗粒的发生和生长

摘要。新粒子形成 (NPF) 是指分子簇的成核及其随后生长到云凝结核 (CCN) 大小范围内，是具有全球意义且与气候相关的大气气溶胶来源。在世界各地的行星边界层 (PBL) 中广泛观察到经典 NPF 从几纳米到 Aitken 模式持续增长，大约 60-70 nm，但在亚马逊中部没有。在这里，在 PBL 中很少观察到经典的 NPF 事件，相反，NPF 开始于对流层上层 (UT)，随后注入亚 50 nm (CN _{< 50}) 粒子进入 PBL 及其随后的生长。然而，我们对亚马逊这些过程的理解的核心方面仍然是个谜。根据亚马逊高塔天文台（ATTO，2014 年 2 月至 2020 年 9 月）六年多的气溶胶和气象数据，我们分析了 217 个事件日的 254 个此类亚马逊增长事件期间的昼夜和季节模式以及气象条件，这表明 PBL 中 10 到 50 nm 之间的颗粒突然出现，然后它们增长到 CCN 尺寸。雨季事件的发生率显着高于旱季，1 月至 6 月的事件发生率为 88%，7 月至 12 月为 12%，这可能是由于冷凝汇 (CS)、大气气溶胶负荷和气象条件。^-1和 0.0011 s ^-1的中值 CS 。生长事件是在白天（74％）期间更频繁和表现出较高的GR（5.9纳米ħ ^-1）相比于夜间事件（4.0纳米ħ ^-1），强调光化学和PBL进化的粒子生长的作用。事件的大约70％呈负异常的等效电势的温度（Δ θ ' _ë） -作为下降气流的标记-和低亮度卫星温度（Tir的) – 作为深对流云的标志 – 与强对流活动过程中来自 UT 的粒子注入非常吻合。关于事件的30％，但是，发生在没有深对流的，部分地在晴朗的天空状况，和具有正Δ θ ' _ë异常。因此，这些事件似乎与下降气流注入无关，并表明存在其他目前未知的亚 50 nm 粒子来源。