Heterogeneous nucleation and subsequent growth of surface water occur on hydrophobic natural substrates under supersaturation; however, this basic physical relationship has been explained only empirically as yet. In order to derive a new method to determine supersaturation at the canopy–air interface, we considered the parameters that contribute to surface water formation (SWF) and examined their importance by field observations at an urban site in the period 2015–2017. We found that both the interfacial and vertical temperature differences ranged 1–3 K and that they were necessary but not sufficient for supersaturated condensation on natural surfaces. Excess supply of moisture must exist and continuously contribute to the growth of the condensed water nuclei, which may originate from external sources such as atmospheric advection. Under the additional moisture supply, SWF appeared not only on the ground soil but also on the vegetation canopy at heights of 1–2 m. We also found that the SWF plays a role in the removal of ground-level air pollutants. The removal efficiency for [SO42− + NO3−] of the deposition flux was estimated as ~ 0.3 mmol (per [Ca2+] meq)/m2(per leaf area) during SWF.

中文翻译：

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过饱和下自然地表地表水的形成：从局部水平衡到空气污染物沉积

在过饱和条件下，疏水性天然基质上发生非均相成核和随后的地表水生长；然而，这种基本的物理关系至今只能凭经验得到解释。为了推导出一种确定冠层-空气界面过饱和度的新方法，我们考虑了有助于地表水形成 (SWF) 的参数，并通过 2015 年至 2017 年期间在城市场地的实地观察检查了它们的重要性。我们发现界面和垂直温差都在 1-3 K 范围内，它们对于自然表面上的过饱和冷凝是必要的，但还不够。必须存在过量的水分供应，并不断促进凝结水核的生长，凝结水核可能来自大气平流等外部来源。在额外的水分供应下，SWF不仅出现在地面土壤上，而且出现在1-2 m高度的植被冠层上。我们还发现 SWF 在去除地面空气污染物方面发挥作用。在 SWF 期间，沉积通量的 [SO42- + NO3-] 去除效率估计为 ~ 0.3 mmol（每 [Ca2+] meq）/m2（每叶面积）。