Objective Since the 21st century, a number of infectious diseases such as SARS and COVID-19 have occurred in succession, all of which show such characteristics as high transmissibility and high incidence rate, with bioaerosol particles as the disseminator thereof. In view of this, it is necessary to take appropriate control measures to reduce the spread of bioaerosol particles. A large number of researches have shown that vertical greening can filter aerosol particles in the air, but there are few researches on the correlation between vertical greening mode and bioaerosol adsorption efficiency. Planners should verify each specific scenario in advance, and combine multiple influencing factors of different greening modes to reduce the spread of bioaerosol particles in communities. Since 2019, the construction of future communities in Zhejiang Province has been launched in an all-round way. The Development and Reform Commission of Zhejiang Province has established an evaluation index system for the pilot establishment. Among them, "building a three-dimensional and multi-level composite greening system by vertical greening" has become a binding indicator for the creation of architectural scenes, and requires that the interior of the building cluster try to prevent viruses and pollutants from entering the community environment and causing cross-contamination through ventilation shafts and other facilities. Therefore, Zhejiang Province has carried out a special study on the future three-dimensional greening of communities to explore a reasonable three-dimensional greening and vertical greening mode. From the perspective of the control effect of vertical greening on biological aerosols, the study takes the future community of Linhai Liujiaojing as the research object, evaluates and predicts the control effect of biological aerosols of vertical greening under actual environmental conditions, and explores the best vertical greening design mode.
Methods Using a numerical simulation model, this research discusses the influence of vertical greening configuration mode of communities with high building density on the concentration of bioaerosols in the environment and, in combination with the two configuration indicators of vertical greening facade coverage (GFR) and vertical greening facade orientation (GO), analyzes the influence of nine vertical greening modes on the concentration of bioaerosols in the environment. Moreover, the research adopts ENVI-met for data analysis. ENVI-met is a predictive three-dimensional microclimate and computational fluid dynamics (CFD) model, which can simulate the interaction of land surface, plants and atmosphere in a complex urban environment. The model can be used for numerical simulation on high-resolution spatial (0.5-10.0 m) and temporal (up to 10 s) grids, based on which the small-scale interaction between buildings, grounds and plants can be analyzed; ENVI-met is widely used in researches on human biometeorology and thermal comfort, which has, in combination with customizable pollutant modules, gradually made aerosol pollutants a focus among relevant researchers. In the developed research model, the interaction of spherical aerosol with air turbulence and material surface can be generated and reproduced in a limited three-dimensional area, which has a given geometric shape of the boundary and medium. Thanks to this, it is now possible to calculate the concentration of aerosol particles in the air by tracking the trajectory thereof.
Results In the GO-4F mode, the dominant wind direction of the vortex is opposite to the GFR-0 mode in the bare wall scenario. The dominant wind direction changes from the bottom of the building to the top, and the vortex center position shifts from the lower left corner to the upper right corner. Since there is a certain positive correlation between wind speed and building height, and vertical greening is vertically distributed along the building facade, vertical greening will have a great influence on the wind field. Due to the blocking effect of vertical greening on turbulence, the vortex velocity between buildings decreases, forming a quiet wind zone in the vortex center. With the increase of GFR, the decreasing effect of vertical greening on the concentration of bioaerosols in the environment can be gradually enhanced.
Conclusion With the increase of GFR, the weakening effect of vertical greening on atmospheric turbulence in the environment is enhanced, leading to the rapid accumulation of bioaerosols in the internal environment of the building cluster; the reduction effect of vertical greening on the concentration of bioaerosols in the environment gradually increases with the increase of GFR, and begins to show a marginal decreasing effect after GFR reaches 67%; under the same GFR conditions, when GO is in the windward direction, it can greatly reduce the concentration of bioaerosols in the environment. In order to control the air transmission of bioaerosols in communities with high building density, and accordingly control the air transmission of diseases in communities, this research, according to the results of numerical simulation research, proposes the following recommendations for vertical greening configuration mode: considering that vertical greening in communities with high building density can effectively reduce the concentration of bioaerosols in the environment, vertical greening should be considered in future community construction; there exists a positive correlation relationship between the value of GFR and the reduction of bioaerosol concentration in the environment, so in actual construction, the GFR index should reach more than 67%; high GFR should be ensured in the main windward side of buildings and in the part of building facade below 30 m from the ground. The introduction of numerical simulation model can effectively evaluate and predict the control effect of different vertical greening modes on the concentration of bioaerosols, so as to optimize the implementation plan of vertical greening in communities.
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