Abstract The initial nucleation of ultrafine particle recently attracts more attention as a key factor in visibility degradation during early haze. In this study, we have performed Density Functional Theory (DFT) calculation to investigate the particle-induced initial nucleation process during early haze. Our calculation results show that the water molecules aggregate surrounding nuclei to form heterogeneous cluster under a certain RH, the synergistic effect of multiple-bonding interactions makes heterogeneous cluster incline to form and stably exist with lower total energy as well as approximately 3–10 times expansionary volume, the hygroscopic growth of aerosol particles would play an important role in affecting the atmospheric visibility. The electron cloud density transferring from the exterior H2O molecule to the interior nuclei in the cluster is characterized by migration effect or nonuniform distribution. The decreasing energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the heterogeneous cluster would lead to a red-shifted absorption wavelength λmax. It exerts the blue, indigo and violet visible-light absorption of corresponding wavelength for NO, NO2, NO3− and O3 heterogeneous clusters to enhance light extinction, thus contributing to visibility degradation, during early haze periods. It helps to intensify the color-enhancing effect of visible light with longer wavelength, such as red, orange as well as yellow light, to promote the evolution of early haze in clean weather period. This study shows that one of the important mechanisms of atmospheric visibility degradation in haze event is the heterogeneous cluster formation in the size range of about 2–4 nm during initial nucleation stage. Our results highlight that prevention of gas-phase chemical species (NO, NO2 and SO2) emission, and also regulatory controls of the concentrations of NO3−, O3 in atmosphere are necessary to prevent deterioration of the air quality in future.

中文翻译：

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基于成核聚类模型的早期雾霾大气能见度退化分析

摘要 超细颗粒的初始成核作为早期雾霾期间能见度下降的关键因素引起了越来越多的关注。在本研究中，我们进行了密度泛函理论 (DFT) 计算，以研究早期雾霾期间粒子诱导的初始成核过程。我们的计算结果表明，在一定的相对湿度下，水分子聚集在原子核周围形成异质簇，多键相互作用的协同作用使异质簇倾向于形成并稳定存在，总能量较低，膨胀率约为3-10倍体积，气溶胶颗粒的吸湿生长将在影响大气能见度方面发挥重要作用。从外部 H2O 分子转移到团簇内部原子核的电子云密度具有迁移效应或分布不均匀的特点。异质簇中最高占据分子轨道 (HOMO) 和最低未占据分子轨道 (LUMO) 之间的能隙减小将导致吸收波长 λmax 红移。它对 NO、NO2、NO3- 和 O3 异质簇施加相应波长的蓝色、靛蓝色和紫色可见光吸收，以增强消光，从而在早期雾霾期间导致能见度降低。有助于加强红光、橙光、黄光等波长较长的可见光的增色作用，促进清洁天气期早期雾霾的演化。该研究表明，雾霾事件中大气能见度降低的重要机制之一是在初始成核阶段形成大小范围约为 2-4 nm 的异质簇。我们的结果强调，防止气相化学物质（NO、NO2 和 SO2）排放，以及对大气中 NO3−、O3 浓度的监管控制对于防止未来空气质量恶化是必要的。