| 1. |
- Cai, Jing, et al.
(författare)
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Elucidating the mechanisms of atmospheric new particle formation in the highly polluted Po Valley, Italy
- 2024
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Ingår i: Atmospheric Chemistry and Physics. - 1680-7316 .- 1680-7324. ; 24:4, s. 2423-2441
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Tidskriftsartikel (refereegranskat)abstract
- New particle formation (NPF) is a major source of aerosol particles and cloud condensation nuclei in the troposphere, playing an important role in both air quality and climate. Frequent NPF events have been observed in heavily polluted urban environments, contributing to the aerosol number concentration by a significant amount. The Po Valley region in northern Italy has been characterized as a hotspot for high aerosol loadings and frequent NPF events in southern Europe. However, the mechanisms of NPF and growth in this region are not completely understood. In this study, we conducted a continuous 2-month measurement campaign with state-of-the-art instruments to elucidate the NPF and growth mechanisms in northern Italy. Our results demonstrate that frequent NPF events (66% of all days during the measurement campaign) are primarily driven by abundant sulfuric acid (8.5×106cm-3) and basic molecules in this area. In contrast, oxygenated organic molecules from the atmospheric oxidation of volatile organic compounds (VOCs) appear to play a minor role in the initial cluster formation but contribute significantly to the consecutive growth process. Regarding alkaline molecules, amines are insufficient to stabilize all sulfuric acid clusters in the Po Valley. Ion cluster measurements and kinetic models suggest that ammonia (10ppb) must therefore also play a role in the nucleation process. Generally, the high formation rates of sub-2nm particles (87cm-3s-1) and nucleation-mode growth rates (5.1nmh-1) as well as the relatively low condensational sink (8.9×10-3s-1) will result in a high survival probability for newly formed particles, making NPF crucial for the springtime aerosol number budget. Our results also indicate that reducing key pollutants, such as SO2, amine and NH3, could help to substantially decrease the particle number concentrations in the Po Valley region.
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| 2. |
- Nie, Yifang, et al.
(författare)
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无线信道建模中二分 K 均值聚类多径分簇算法
- 2023
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Ingår i: Dianbo Kexue Xuebao/Chinese Journal of Radio Science. - 1005-0388. ; 38:2, s. 284-291
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Tidskriftsartikel (refereegranskat)abstract
- In order to rationally allocate multi-path component (MPC) of wireless channels to different clusters, a multi-path clustering algorithm based on Bisecting K-means clustering was proposed for millimeter-wave channels to solve the problem of partial optimization of traditional K-means clustering methods. The MPC clustering was implemented based on the cluster split and iteration computation strategy, when the Mahalanobis distance (MD) was regarded as the multipath component distance (MCD). The experiment measurement in indoor millimeter-wave channel was conducted to verify the effectiveness and feasibility of the proposed method. The experimental results show that the clustering result of proposed method is more rational than those of traditional K-means clustering methods, and the highly correlated MPCs are reasonably and uniquely allocated to the same cluster.
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