Aerosol particles are a complex component of the atmospheric system which influence climate directly by interacting with solar radiation, and indirectly by contributing to cloud formation. The variety of their sources, as well as the multiple transformations they may undergo during their transport (including wet and dry deposition), result in significant spatial and temporal variability of their properties. Documenting this variability is essential to provide a proper representation of aerosols and cloud condensation nuclei (CCN) in climate models. Using measurements conducted in 2016 or 2017 at 62 ground-based stations around the world, this study provides the most up-to-date picture of the spatial distribution of particle number concentration (N_tot) and number size distribution (PNSD, from 39 sites). A sensitivity study was first performed to assess the impact of data availability on N_tot's annual and seasonal statistics, as well as on the analysis of its diel cycle. Thresholds of 50 % and 60 % were set at the seasonal and annual scale, respectively, for the study of the corresponding statistics, and a slightly higher coverage (75 %) was required to document the diel cycle.Although some observations are common to a majority of sites, the variety of environments characterizing these stations made it possible to highlight contrasting findings, which, among other factors, seem to be significantly related to the level of anthropogenic influence. The concentrations measured at polar sites are the lowest (∼ 10² cm⁻³) and show a clear seasonality, which is also visible in the shape of the PNSD, while diel cycles are in general less evident, due notably to the absence of a regular day–night cycle in some seasons. In contrast, the concentrations characteristic of urban environments are the highest (∼ 10³–10⁴ cm⁻³) and do not show pronounced seasonal variations, whereas diel cycles tend to be very regular over the year at these stations. The remaining sites, including mountain and non-urban continental and coastal stations, do not exhibit as obvious common behaviour as polar and urban sites and display, on average, intermediate N_tot (∼ 10²–10³ cm⁻³). Particle concentrations measured at mountain sites, however, are generally lower compared to nearby lowland sites, and tend to exhibit somewhat more pronounced seasonal variations as a likely result of the strong impact of the atmospheric boundary layer (ABL) influence in connection with the topography of the sites. ABL dynamics also likely contribute to the diel cycle of N_tot observed at these stations. Based on available PNSD measurements, CCN-sized particles (considered here as either >50 nm or >100 nm) can represent from a few percent to almost all of N_tot, corresponding to seasonal medians on the order of ∼ 10 to 1000 cm⁻³, with seasonal patterns and a hierarchy of the site types broadly similar to those observed for N_tot.Overall, this work illustrates the importance of in situ measurements, in particular for the study of aerosol physical properties, and thus strongly supports the development of a broad global network of near surface observatories to increase and homogenize the spatial coverage of the measurements, and guarantee as well data availability and quality. The results of this study also provide a valuable, freely available and easy to use support for model comparison and validation, with the ultimate goal of contributing to improvement of the representation of aerosol–cloud interactions in models, and, therefore, of the evaluation of the impact of aerosol particles on climate.

中文翻译：

---

粒子数浓度和大小分布的季节性：从全球大气监视网 (GAW) 近地表观测站网络检索的全球分析

气溶胶粒子是大气系统的一个复杂组成部分，它通过与太阳辐射的相互作用直接影响气候，并通过促成云的形成间接影响气候。它们来源的多样性，以及它们在运输过程中可能经历的多重转变（包括湿沉降和干沉降），导致它们的性质发生显着的时空变化。记录这种可变性对于在气候模型中正确表示气溶胶和云凝结核 (CCN) 至关重要。本研究使用 2016 年或 2017 年在全球 62 个地面站进行的测量，提供了粒子数浓度空间分布的最新图片 ( N _tot）和数量大小分布（PNSD，来自 39 个站点）。首先进行了一项敏感性研究，以评估数据可用性对N _tot的年度和季节性统计数据的影响，以及对其diel 周期分析的影响。分别在季节性和年度尺度上设置了 50% 和 60% 的阈值，用于研究相应的统计数据，并且需要稍高的覆盖率 (75%) 来记录日照周期。尽管大多数站点的一些观察结果是共同的，但这些站点的各种环境特征使得可以突出对比发现，除其他因素外，这些发现似乎与人为影响水平显着相关。在极地测得的浓度最低 ( ∼  10 ²  cm ^-3 ) 并显示出明显的季节性，这在 PNSD 的形状中也可见，而昼夜循环通常不太明显，主要是由于缺乏在某些季节有规律的昼夜循环。相比之下，城市环境特征的浓度最高（∼  10 ³ –10 ⁴  cm ^-3) 并且没有表现出明显的季节性变化，而这些站点一年中的昼夜周期往往非常规律。其余站点，包括山区和非城市大陆和沿海站点，不像极地和城市站点那样表现出明显的共同行为，并且平均显示中间N _tot ( ∼  10 ² –10 ³  cm ^-3）。然而，在山区测量的颗粒浓度通常低于附近的低地站点，并且由于大气边界层 (ABL) 与地形相关的强烈影响，可能会表现出更明显的季节性变化。网站。ABL 动力学也可能有助于在这些站点观察到的N _tot的日夜循环。根据可用的 PNSD 测量，CCN 大小的粒子（此处视为> 50  nm 或> 100  nm）可以代表N _tot的几个百分比到几乎所有，对应于大约 10 到 1000 cm 的季节性中位数^{- 3}，具有季节性模式和站点类型的层次结构与观察到的N _tot大致相似。 总的来说，这项工作说明了原位测量的重要性，特别是对于气溶胶物理特性的研究，因此强烈支持开发一个近地表天文台的广泛全球网络，以增加和统一测量的空间覆盖范围，并保证数据的可用性和质量。本研究的结果还为模型比较和验证提供了有价值、免费且易于使用的支持，其最终目标是有助于改进模型中气溶胶 - 云相互作用的表示，因此，评估气溶胶颗粒对气候的影响。