Abstract. Dry deposition is a fundamental process that removes particles from the atmosphere, and therefore directly controls their lifetime and total impact on air quality and radiative forcing. The processes influencing dry deposition are poorly constrained in models. Seasonal changes in dry deposition remain uncertain due to the lack of observations over multiple seasons. We present measurements of size-resolved sub-micron particle deposition from a flux study that surveyed all four major seasons. Particle concentrations and therefore fluxes were highest in the summer and lowest in the winter. Size-dependent deposition velocities in all seasons were consistent with previously observed trends, however, our observations show a 130 ± 60 % increase in wintertime deposition velocity compared to the summer, which is not currently captured in size-resolved deposition models. We explore the influence of scalar gradients and changes in environmental conditions as possible drivers of this increase. We find that phoretic effects, such as thermophoresis, and the addition of snow to the canopy had negligible impacts on our canopy level measurements. While turbophoresis impacted the observed seasonal changes in size-resolved particle deposition velocity, it did not fully explain the observed differences between the summer and winter. We suggest that the increase in deposition velocity is instead caused by changes to the leaf-level conditions and physiology during the wintertime, which increase interception of particles.

中文翻译：

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松林大小分辨颗粒沉降的季节变化和环境条件对干沉降的影响

摘要。干沉降是从大气中去除粒子的基本过程，因此直接控制它们的寿命以及对空气质量和辐射强迫的总体影响。影响干沉积的过程在模型中的约束很差。由于缺乏对多个季节的观测，干沉降的季节变化仍然不确定。我们从一项调查所有四个主要季节的通量研究中展示了尺寸分辨的亚微米颗粒沉积的测量结果。颗粒浓度和通量在夏季最高，冬季最低。所有季节的大小相关沉积速度与先前观察到的趋势一致，然而，我们的观察显示，与夏季相比，冬季沉积速度增加了 130 ± 60%，目前尚未在尺寸分辨的沉积模型中捕获。我们探讨了标量梯度的影响和环境条件的变化作为这种增加的可能驱动因素。我们发现泳动效应，例如热泳，以及向树冠添加雪对我们的树冠水平测量的影响可以忽略不计。虽然涡轮电泳影响了观测到的尺寸分辨颗粒沉积速度的季节性变化，但它并没有完全解释观测到的夏季和冬季之间的差异。我们认为沉积速度的增加是由冬季叶片水平条件和生理的变化引起的，这增加了颗粒的拦截。我们发现泳动效应，例如热泳，以及向树冠添加雪对我们的树冠水平测量的影响可以忽略不计。虽然涡轮电泳影响了观测到的尺寸分辨颗粒沉积速度的季节性变化，但它并没有完全解释观测到的夏季和冬季之间的差异。我们认为沉积速度的增加是由冬季叶片水平条件和生理的变化引起的，这增加了颗粒的拦截。我们发现泳动效应，例如热泳，以及向树冠添加雪对我们的树冠水平测量的影响可以忽略不计。虽然涡轮电泳影响了观测到的尺寸分辨颗粒沉积速度的季节性变化，但它并没有完全解释观测到的夏季和冬季之间的差异。我们认为沉积速度的增加是由冬季叶片水平条件和生理的变化引起的，这增加了颗粒的拦截。它并没有完全解释观察到的夏季和冬季之间的差异。我们认为沉积速度的增加是由冬季叶片水平条件和生理的变化引起的，这增加了颗粒的拦截。它并没有完全解释观察到的夏季和冬季之间的差异。我们认为沉积速度的增加是由冬季叶片水平条件和生理的变化引起的，这增加了颗粒的拦截。