Numerical Simulation And Experimental Study On The Mitigation Of Fugitative Particulate Matter By Vegetation Barriers

Atmospheric particle pollution is recognized as the most representative and most harmful type of pollution,and has become an important factor restricting the quality of atmospheric environment in many cities.Compared to organized sources of particulate matter,there is a lack of systematic research on the issue of open source of unorganized particulate matter.As a typical open source of dust,livestock farms are the main source of airborne particulate pollutants.Strategically placed barriers can be used to reduce the accumulation of contaminants in the air and slow down the probability of transmission to adjacent areas on the diffusion path of the fugitive source particulate contaminants.In many production practices,vegetation barriers are also constructed to reduce wind speed interception of pollutants in blocked air.However,due to the lack of scientific basis for plant species selection,planting layout and management,its application in production practice is limited.Therefore,this subject has carried out research on vegetation barriers to slow down the diffusion and migration of particulate pollutants;comprehensively considers the concentration of particulate pollutants in the air and the characteristics and selectivity of plant leaf and leaf dust to evaluate the retarding ability of selected vegetation to dissipate particulate matter.This thesis begined with the computational fluid dynamics numerical simulation study,established the calculation model of the dust-containing particle flow through the vegetation barrier,comprehensively investigates the fluid properties such as particle concentration and transmission velocity in the fluid domain,and predicts the barrier collection efficiency?CE?of the vegetation barrier to particulate matter.Then,according to the characteristics of natural conditions in Jilin Province,vegetation barriers were established outside the mechanical vent of a typical poultry house.By analyzing the differences of particle concentrations of the up-and-down wind,the micro-morphology of the leaf surface and the characteristics of the dust-retaining,the block ability of the vegetation to the dissipative particles,and the tree species with relatively strong blocking ability were selected.Finally,the pioneering attempt to create an open particulate escape source by simulating the dust source form of the livestock and poultry farm,construct single-row and double-row barriers for the selected dominant vegetation species,and systematically evaluate the block effect of the selected species barrier.The research results have improved the research methods and technical means for the targeted selection of vegetation types and building barriers that are easy to block the absorption of particulate matter in specific regions and environments.The specific research results are as follows:1.Results of numerical simulations showed that the geometry of the vegetation barrier has a great influence on the dust-blocking efficiency of the coarse particles,but has no significant effect on the dust-blocking effect of the fine particles.Compared with original size,increasing the height and leaf surface area density?LSAD?of the tree both helped to increase the vegetation block rate.Increasing the width of the tree had the greatest effect on particle collection compared to increase the height or LSAD.Adding another row of tree also increased the capability of the tree in wind speed reduction and particle collection,while row spacing did not show great effect.2.The evaluation results of different vegetation barriers on the blockage ability of the particulate matter at the mechanical exhaust outlet of the laying house show that the particle concentration of the downwind sampling point is significantly lower than that of the upwind sampling point due to the occurrence of the vegetation barrier?p<0.05?.Specifically,compared with the control experiment without vegetation barrier,the vegetation barrier formed by Padus Virginiana‘Red Select Shrub'?PV_RSS?has the highest collection efficiency,that is,the best retardation effect on particulate matter,and its PM_2.5 and PM₁₀ The block rates were 47.24%±4.33%and41.13%±5.83%,respectively.Dust sources,ambient wind speeds,and vegetation leaf characteristics may be the main factors leading to CE differences among different vegetation barriers.At the same time,it has been found that the rough surface of the vegetation leaves can help intercept more particulate matter,although it is also affected by other factors?such as blade angle,PM and wind interaction?,these factors need further study.The vegetation barrier formed by PV_RSS exhibits optimal blocking capacity and can selectively intercept particulate matter mainly related to N,Na,Mg,P,S and Cl.The blocking ability of the five plants in the study by the barrier to the particulate matter was as follows:Padus Virginiana‘Red Select Shrub'?PV_RSS?>Winged Euonymus?WE?>Malus Spectabilis?MS?>Acer Saccharum Marsh?ASM?>Padus Maackii?PAA?.3.According to the results of the test of the barrier capacity of the PV_RSS vegetation barrier,it can be seen that when the natural wind speed is about 4.8 m/s,the blocking ability of PM_2.5 and PM₁₀ can reach 46.01%±26.79%and39.13%±27.09%.Compared with a single row of vegetation,the dust retention capacity of the two rows of PV_RSS vegetation barrier is significantly enhanced,especially when the row spacing is double the height of the tree.This spacing can provide for garden protection,desert control,dust control as the theoretical reference for the planting spacing of vegetation.Through the setting and analysis of the test method,a general evaluation method for vegetation barrier particle detection is obtained.This method is not limited by the test environment,tree planting growth management,livestock production site and management,etc.The dust retention test can be used as a means to evaluate the efficiency of the plant barrier blockage.