Abstract Atmospheric new particle formation (NPF) is an important source of submicron particles. In remote background environments where local sources are scarce such processes may impact significantly on climate-relevant parameters. On the other hand, in urban environments, newly-formed particles are adding up to submicron particles emitted from primary sources. As the exact mechanism which triggers NPF still remains elusive, so are the circumstances for simultaneous occurrence of such events in two different environments (urban vs. regional background). In this study, concurrent number size distribution measurements were conducted in the urban environment of Athens and at the regional background site of Finokalia, Crete, located 340 km away and spanning a 2-year period. It occurred that the relative frequency of NPF was similar at both sites (around 20%), with a higher frequency during spring and autumn at the urban site, while at the background site most events took place in August and December, during the studied period. There were 35 event days when NPF took place at both sites simultaneously, all associated with air masses originating from the Northern sector, indicating the presence of regional events in the extended geographical area and characterized by low condensation sink (CS). By comparing the common with the non-common class I NPF episodes, we conclude that the conditions applying when regional NPF events with growth are observed in the same day at the surface level of both areas, are: (i) lower CS, (ii) higher SO2 concentrations, (iii) lower RH, and finally (iv) lower formation and growth rates than those observed during the site-specific and more rapidly evolving NPF events.

中文翻译：

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关于东地中海新粒子形成的区域方面：基于长期观察的背景和城市地点之间的比较研究

摘要 大气新粒子形成（NPF）是亚微米粒子的重要来源。在当地资源稀缺的偏远背景环境中，此类过程可能会对气候相关参数产生重大影响。另一方面，在城市环境中，新形成的颗粒加起来就是主要来源排放的亚微米颗粒。由于触发 NPF 的确切机制仍然难以捉摸，因此在两种不同环境（城市与区域背景）中同时发生此类事件的情况也是如此。在这项研究中，在雅典的城市环境和位于 340 公里外的克里特岛 Finokalia 的区域背景站点中，同时进行了数量大小分布测量，时间跨度为 2 年。发现两个站点的 NPF 相对频率相似（约 20%），城市站点的春季和秋季频率较高，而背景站点的大多数事件发生在研究期间的 8 月和 12 月. 有 35 个事件日在两个地点同时发生 NPF，所有事件都与源自北部地区的气团有关，表明在扩展的地理区域中存在区域性事件，并以低冷凝汇 (CS) 为特征。通过比较常见的和非常见的 I 类 NPF 事件，我们得出结论，当在同一天在两个区域的表面水平观察到区域性 NPF 事件时，适用的条件是：（i）较低的 CS，（ii） ) 较高的 SO2 浓度，(iii) 较低的 RH，