Abstract Both PM2.5 and visibility are important physical parameters to measure the air pollution condition. This paper first provided a new normalization approach for the relationship between PM2.5 and visibility in heavy pollutant region, which realized a mathematical calculation for two different physical parameters based on non-dimensional data process (also called Min-Max normalization). The normalization relationship showed a power function (y = axb) with high correlation coefficients. The inflection points of the maximum power function curvature composed the theoretical threshold range of PM2.5 for improving or deteriorating the visibility. In the case city of north China, the threshold range of PM2.5 was 112–121 μg·m−3 corresponding to the visibility range 4.5–5.9 km. Within the threshold range, the mean concentration of main pollutant components was 106 μg·m−3. The mean extinction coefficient, bext of 743.5 Mm−1, was mainly contributed by organic matter (34%), ammonium nitrate (19%), ammonium sulfate (18%) and elemental carbon (13%). When PM2.5 was below the range, the visibility increased significantly with the slow decrease of PM2.5. When PM2.5 exceeded the range, the visibility reduced seriously due to the saturated extinction contribution of the main pollutants. The new normalization approach theoretically revealed the significance of threshold and how to improve visibility by controlling PM2.5 at different pollution stages.

中文翻译：

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PM2.5与能见度归一化关系的新方法及理论阈值，以华北地区为例

摘要 PM2.5和能见度都是衡量空气污染状况的重要物理参数。本文首先提出了一种新的重污染区PM2.5与能见度关系的归一化方法，实现了基于无量纲数据处理的两种不同物理参数的数学计算（也称为Min-Max归一化）。归一化关系显示具有高相关系数的幂函数（y = axb）。最大幂函数曲率的拐点构成了PM2.5改善或恶化能见度的理论阈值范围。以华北为例，PM2.5阈值范围为112-121 μg·m-3，对应的能见度范围为4.5-5.9公里。在阈值范围内，主要污染物成分平均浓度为106 μg·m-3。平均消光系数为 743.5 Mm-1，主要由有机物 (34%)、硝酸铵 (19%)、硫酸铵 (18%) 和元素碳 (13%) 贡献。当PM2.5低于该范围时，能见度显着增加，PM2.5缓慢下降。当PM2.5超范围时，主要污染物的饱和消光贡献导致能见度严重下降。新的归一化方法从理论上揭示了阈值的重要性以及如何通过控制不同污染阶段的 PM2.5 来提高能见度。5 低于该范围，能见度显着增加，PM2.5 缓慢下降。当PM2.5超范围时，主要污染物的饱和消光贡献导致能见度严重下降。新的归一化方法从理论上揭示了阈值的重要性以及如何通过控制不同污染阶段的 PM2.5 来提高能见度。5 低于该范围，能见度显着增加，PM2.5 缓慢下降。当 PM2.5 超过该范围时，由于主要污染物的饱和消光贡献，能见度严重下降。新的归一化方法从理论上揭示了阈值的重要性以及如何通过控制不同污染阶段的 PM2.5 来提高能见度。