Research On Mode Of Motor Vehicle Pollutant Diffusion Of Open-Urban Street

In recent years, with the development of economy, the quantity of vehicle isincreasing rapidly especially in urban. By the end of 2007, the number of vehiclesin China is more than 150 millions. The vehicle emission level is much higher inChina than that in westerns countries just because of the low manufacturinglevel ,oil quality and emission standard. With the vehicle emission occupies'increasing, the vehicle emissions becomes a main pollution source .Manyresearches have illustrated that the form of environmental pollution in city istransforming from the smoke pollution to mixed pollution. Therefore, it isnecessary to research on the affection of vehicle emission on environment.The diffusion characteristic of vehicle emissions is complicated in city streets,which has the same and the different diffusion with atmosphere sometimes. It isinfluenced not only by meteorological factors, but also by other specific conditions,such as urban terrain, and urban heat, etc. According to the height and the densityof the buildings, the city streets are divided into open-urban street andcanyon-urban street. Pollutant has different diffusion in different type streets. Inorder to meet the need of environmental disposal and plan, it is necessary to studyon the distribution characteristic of diffusion of airflow, and vehicle emissiondeeply.Taking diffusion characteristic, influence factors, and distribution characteristicas study projects, the affection degree of the weather and the traffic on the diffusionof vehicle emission is analyzed from the angle of weather and traffic. The analysisresults show that the temperature, wind direction, speed, and the height ofatmospheric mixed have strong effect on the diffusion of vehicle emission inopen-urban streets. However, the factors of traffic just like the vehicle emissionlevel, flow, and vehicles type ratio have strong effect on the diffusion of vehicleemission in open-urban streets The field experiments on monitoring were carried out in which the RenminAvenue were selected as typical road sections in Changchun. Pollutant (CO, NO2)concentration by center of and both sides of the streets is obtained by difficultmethods at each sampling interval. According to field monitoring and data analysis,The results show what pollutant (CO, NO2)concentration were grossly decreasedwith the increase of distance, but variation of concentration of carbon monoxidewas obvious than concentrations of nitrogen dioxide. Pollutant (CO, NO₂)concentration of pollution source on the up-wind was lower than concentration onthe down-wind, wind direction be sensitive for open-urban street. After analyzingthe relativity, coefficient between motor vehicles flow and motor vehicles pollutant(CO, NO2) concentration are 0.64 and 0.478, pollutant CO concentration haddistinct linear correlation with flow by t test. The degree of dependent reachedsignificant level. There is not linear correlation between wind speed and pollutant(CO, NO2) concentration by the t-test. CO concentration was lower than nationalair quality secondary standard, while NO2 concentration was higher than nationalair quality third standard. Air quality of monitored road section was very general.Based on understanding influencing factors of pollutant transport and diffusion,established line source diffusion model by gradient-diffusion theory and statisticaltheory of turbulence. According to light wind characteristics of open-urban street,line source diffusion model includes wind condition and light wind condition.meanwhile, a set of simplified calculation method was established for raisingforecast accuracy. The model was verified with the help of experimental data, theresults show that predictive value of CO concentration have higher accuracy,calculated concentration and measured concentration correlation coefficient was0.89, the whole-error is 1.4%,CO calculated concentration had distinct linearcorrelation with measured concentration. NO2 calculated concentration andNO2measured concentration correlation coefficient was 0.625, calculatedconcentration of NO2 had distinct linear correlation with measured concentration,but the whole-error is big.The results provide theoretical basis for monitoring the distribution of motorvehicle pollutant, provides qualitative and quantitative analysis, urban streetconstruction and traffic control. The conclusion has practical significances toprotective measures of pollutants.