Simulation On The Characteristics Of Pollutants Dispersion In Urban Street Canyon

With the continuous increase of urban population in China,the problem of air pollution on traffic roads caused by the proliferation of vehicles and road congestion has become more and more serious.Based on the analysis of road traffic conditions and atmospheric pollution characteristics in Xi'an,this paper uses the OSPM model to simulate the NO₂ concentration in different street patterns,and analyzes the influence of different architectural layouts on the diffusion of pollutants in the streets.The results were as follows:?1?From 2009 to 2016,the annual average concentration of SO₂ in Xi'an showed a downward trend,and the annual average concentration of NO₂ and PM₁₀0 showed an upward trend.From November to next February,the concentration of SO₂ and NO₂ was the highest in the whole year,and from July to September.The SO₂ and NO₂concentrations are small.The PM₁₀0 concentration appeared high from October to March of the following year,and the lowest value occurred from June to July each year.?2?The number of motor vehicles in Xi'an increased from an average of approximately 19.7%from 1999 to 2016.As of the end of 2016,there were 2.55 million vehicles.Urban roads between and 8:00-11:00 and 14:00-18:00 are peak traffic periods.The traffic volume in the South Second Ring Road is the largest.The average traffic volume reaches 9600 vehicles/hour.The traffic volume at the bridge mouth is the smallest and the average traffic volume is 900 vehicles/hour.?3?The simulated NO₂ concentration increased from 6.4?g/m³ to 140?g/m³ when the vehicle flow rate increased from 50 to 9000 vehicles/hour;Wind speed increased from 0 to 7m/s,simulated NO₂ concentration decreased from 103.4?g/m³ to 51.5?g/m³;when the wind direction angle increased from 0°to 360°,the simulated NO₂concentration showed a cyclic change,the highest was 80.2?g/m³and the lowest was28.4?g/m³;the street aspect ratio increased from 0.3 to 4.1,the simulated NO₂concentration increased from 48.7?g/m³to 82.5?g/m³.Therefore,traffic flow,wind speed,wind direction,and street aspect ratio are sensitive parameters of the OSPM model,and temperature is an insensitive parameter.?4?The NO₂ concentration of the sidewalks on both sides of North Street,East Street,Tai Yi Road,Wen Yi Road,Qiao Zi Kou Road,You Yi West Road,Gao Xin Street and South Second Ring Road is the most serious,and the concentration of NO₂ is mainly between 150-230?g/m³,and the street pollution with less traffic is less.The variation of NO₂ concentration in the street is basically the same as the variation of vehicle flow,and there is a difference between the variation of the wind speed and the traffic volume when the wind speed and wind speed change greatly.?5?OSPM was used to study the influence of different building layout on pollutant dispersion in streets The concentration of NO₂ in the asymmetric Street Valley is small.High concentration of NO₂ when close to the symmetrical Street.The NO₂concentration on the windward side of the street canyon does not change with the height of the simulation point,and the leeward side decreases.When the height is higher than35 m,the concentration on both sides is the same and does not change.When the aspect ratio in the street canyon is constant,the height of the building is lower and the circulation area is smaller.The concentration will be higher.The building height increased from 70m to 110m,and the NO₂ concentration only decreased by 4.1?g/m³.