Prediction Of Maximum Allowable Vehicles In Transit In Xi’an Under The Constraint Of Environmental Carrying Capacity

In recent years,Shaanxi Province has been included in the"three zones and ten groups"of the key national air pollution prevention and control areas due to the continuous heavy pollution weather.Exhaust pollution caused by the rapid growth of motor vehicles has become a major source of urban air pollution.Motor vehicle exhaust pollutants seriously affect the urban road environment and residents’physical and mental health.Although the relevant departments of Shaanxi Province have adopted a series of measures to reduce the emissions of motor vehicles and alleviate the pressure on urban traffic environment,the number of motor vehicles in China is still increasing year by year,and the problem of traffic congestion is becoming increasingly serious.The predicted amount of in-transit vehicles under force constraints has very important value.This article analyzes and researches from two key aspects:one is from the environmental aspect,and the other is from the motor vehicle aspect.The two aspects are combined by solving the maximum allowable amount of motor vehicles in transit.The main research contents are as follows:（1）The average number of days of light pollution and above in Xi’an accounts for51.23%.The main pollutant in the year is mainly PM_2.5.Using SPSS to perform a Pearson correlation analysis between pollutant concentrations,pollutants,and meteorological conditions in different seasons,it was concluded that changes in SO₂,NO₂,and CO concentrations correspond to changes in PM particulate matter concentrations;average wind speed,average temperature,and precipitation Significantly related to various pollutants.At the same time,the HYSPLIT model was used to simulate the daily airflow trajectory of 48h arriving in Xi’an,and the clustering analysis was used to obtain the representative air pollution transport paths and potential sources for the four seasons.The results show that PM particulate pollutants mainly come from air mass transport in the northwestern region;the potential sources of particulate matter in the spring and winter seasons are mainly concentrated in the southern Shaanxi region of Shaanxi.（2）Established a detailed calculation method for motor vehicle pollution emission inventory.The emission factor method was used to estimate the 2017 Xi’an motor vehicle pollutant emission inventory.The results are as follows:The total annual emissions of vehicle pollutants CO,HC,NO_x,PM_2.5,PM₁₀,NH₃,SO₂,and VOC in Xi’an are 356,200 tons,24,200 tons,52,800 tons,20,200 tons,0.25 10,000 tons,0.09million tons,202,000 tons,18,600 tons.Among them,small and medium-sized passenger cars are the main pollution sources of CO,NH₃and SO₂ emissions;for NO_x,the contribution of medium and heavy trucks reached 54.72%;PM_2.5 and PM₁₀emitted the highest proportion of heavy trucks,49.12%,50.11%.（3）Using the road network of Xi’an as the distribution base,use satellite videos to estimate the traffic volume of relevant roads,and infer the composition of vehicle models on different roads within the Third Ring Road of Xi’an.On the basis of this research road network,combined with Arc GIS technology,through the screening of line source roads,the spatial distribution of motor vehicle emission inventory,the spatial distribution characteristics of pollutant emissions were studied.The results show that in2017,the emission of motor vehicle pollution in Xi’an showed an obvious regional distribution characteristic.Its spatial distribution is mainly based on the third ring road,and the emissions in the northeast region are relatively large.Road sections with large traffic flow,such as national highways and highway sections,have relatively large pollutant emissions,and the linear distribution is more obvious on the spatial distribution map.（4）Under the basic principles of three constraints:total pollution,pollution emissions,and traffic flow,a target optimization model for the maximum allowable amount of vehicles in transit is constructed.Firstly,the concept and characteristics of traffic environmental capacity were introduced,and a calculation model of traffic atmospheric environmental capacity based on the improved atmospheric single-box model was proposed,and the selection criteria of various parameters of the model were analyzed.Secondly,a vehicle exhaust gas pollutant diffusion model solved by a box model was constructed;the influence of road capacity on the actual traffic flow of the target section was analyzed,and a target optimization model for the maximum allowable amount of motor vehicles in transit was constructed on the basis of this,Finally,the LINGO software was used to calculate the maximum traffic flow limit that99 target roads could bear.The results show that the main urban area of Xi’an should have a traffic flow limit of less than 274,000 vehicles per hour.At this scale,the traffic and environmental systems of the main urban area of Xi’an are benign and can meet the city’s capacity to accommodate motor vehicles in transit.It is hoped that the above studies can provide data references for reflecting the air pollution situation in Xi’an,provide a basis for making scientific and reasonable traffic management and control measures,and provide a quantitative method for the design of transportation planning and considering environmental pollution control.