Chemical transport models (CTM) tend to perform poorly in simulating pollution processes under weak turbulent diffusion conditions. In this study, we address this issue from the perspectives of vertical grid resolution and vertical mixing schemes. Three vertical grid resolution configurations (L4, L12, L40) with the CHIMERE model are evaluated during a winter episode, which includes a heavy pollution episode (PE) in the Paris region. The results emphasize the significance of vertical grid resolution, particularly noticeable during nighttime, and consequently impacts CHIMERE simulations under nocturnal stable conditions. Consistent improvement in CTM modeling is observed with refined vertical resolutions and the first layer height based on a simple linear vertical diffusion scheme defined as the initial Kz diffusion (IKD) scheme. Compared to the other two configurations, the finest configuration (referred to as L4-IKD) demonstrates an average improvement in root mean square error of 23.26 % and 25.09 % on regular days (RD) and 62 % and 129 % during PE, respectively. However, simulations using the 1.5-order turbulence kinetic energy (TKE) based eddy diffusivity closure scheme, named the new eddy diffusion (NED), are more sensitive to the first layer height setup. Excessively fine first-layer heights can lead to inaccurate TKE calculations. Generally, models with low vertical grid resolution can reasonably predict air quality on RD or during light pollution events but struggle with heavy PEs. One straightforward enhancement strategy involves adding an extra fine first layer height in CTM simulations, resulting in an average 50.10 % improvement from L4-IKD to L12-IKD during PE. Another strategy is enhancing the model's vertical diffusion scheme, which improved the CTM modeling by 26.67 % compared with IKD during PE under identical vertical grid resolution.

中文翻译：

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垂直网格分辨率和湍流扩散不确定性对化学输运建模的影响


化学输运模型 （CTM） 在模拟弱湍流扩散条件下的污染过程时往往表现不佳。在本文中，我们从垂直网格分辨率和垂直混合方案的角度解决了这个问题。在冬季事件期间，使用 CHIMERE 模型评估了三种垂直网格分辨率配置（L4、L12、L40），其中包括巴黎地区的重污染事件 （PE）。结果强调了垂直网格分辨率的重要性，在夜间尤其明显，因此会影响夜间稳定条件下的 CHIMERE 模拟。通过精细的垂直分辨率和基于定义为初始 Kz 扩散 （IKD） 方案的简单线性垂直扩散方案的第一层高度，可以观察到 CTM 建模的持续改进。与其他两种配置相比，最好的配置（称为 L4-IKD）在正常日 （RD） 和在 PE 期间的均方根误差平均分别提高了 23.26% 和 25.09%，在 PE 期间分别提高了 62% 和 129%。然而，使用基于 1.5 阶湍流动能 （TKE） 的涡流扩散率闭合方案（称为新的涡流扩散 （NED））的模拟对第一层高度设置更敏感。过细的首层高度会导致 TKE 计算不准确。一般来说，垂直网格分辨率低的模型可以合理地预测 RD 或光污染事件期间的空气质量，但对重 PE 的预测则很困难。一种简单的增强策略涉及在 CTM 模拟中添加额外的精细第一层高度，从而在 PE 期间从 L4-IKD 到 L12-IKD 平均提高 50.10%。 另一种策略是增强模型的垂直扩散方案，在相同的垂直网格分辨率下，与 PE 期间的 IKD 相比，CTM 建模提高了 26.67%。