| In recent years,haze weather has been frequent in China,and the coverage area is getting bigger and bigger.Studies have shown that PM2 5 is closely related to the formation of haze weather.PM2 5 has a small particle size and can directly enter bronchioles and alveoil,which pose a great threat to human health.In addition,people's demand for green and healthy living,working and travelling environment is becoming more and more intense.Therefore,it is necessary to further study the changing law of PM2.5.In this paper,the means of measurement and numerical simulation are used to study the law of time and vertical variation of PM2 5 mass concentration and its influencing factors.The measurement is carried out in a high-rise building in Tianjin,and numerical simulation is carried out by using CFD software FLUENT.Due to the limitation of measurement conditions,this study is aimed at the time range of 8:00 to 20:00 and the height range of 1-28 layers.The results of the study show that:The time change law of PM2.5 mass concentration and its influence factors:(1)The fitting equation of PM2.5 time change law is y = 0.0873x3-1.3129x2 + 2.2467x +102.07.The concentration value of morning and evening is greater than that in the afternoon.The maximum value is at 8:00 and the minimum is at 17:00.(2)The time change law of PM2 5 has nothing to do with floor height.(3)The time change law of east and south is "rising-falling-rising",and the time change law of west and north is"falling-rising".(4)The time change law of PM2.5 is closely related to the change of temperature and the morning and evening rush hours.The vertical change law of PM2.5 mass concentration and its influence factors:(1)The vertical change law of PM2.5 presents the type of double peaks and valleys,the peak values are in level 11 and 22,and the valley values are in level 6 and 16.PM2.5 in the vertical direction shows the periodic changes in every 10 layers.(2)The vertical distribution of PM2.5 shows consistence under different orientations,times and pollution levels.The PM2.5 orientation distribution is positively correlated with the dominant wind direction and the seasonal wind in Tianjin.The average change amplitude of PM2.5 is negatively correlated with the pollution levels of PM2.5,and is also related to the morning and evening rush hours of traffic.(3)Under the driving of wind,the particles will form wall-climbing effect along the wall.Increasing the wind speed is conducive to the diffusion of PM2.5.(4)With the increase of the intensity of pollution sources,PM2.5 tends to accumulate in the lower part of the building.(5)Within a certain range,increasing the distance between pollution sources and buildings in the horizontal direction will increase the overall PM2.5 pollution level on the building surface.The center of PM2.5 pollution shifts along with the movement of pollution sources in the vertical direction.(6)Increasing the width of buildings will help to reduce the level of PM2.5 pollution.The research content of this paper can guide people to choose what kind of floor has the best living and working environment.For a special occasion like a hospital and a nursing home,the research can help people with a weak body to choose to live and treat in the less polluted floors of PM2.5.In addition,it can also play a positive role in guiding the prevention and control of air pollution in urban high-rise buildings. |
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