The Diffusion Characteristics And Influencing Factors Of Particulate Pollutants Of Vehicle Exhaust

In recent years, because of the serious environmental pollution, the disastrous fog and haze occurs frequently in China,having become the most prominent problem. Take Wuhan as an example, the haze continued 27 days in October and 22 days in November, which was the highest history record since 1961. The haze pollution is caused by the suspended particles in the air, which can invade lungs from the respiratory tract, causing a variety of diseases and doing harm to the human health. Suspended particles in the air come mainly from fossil fuels, such as coal combustion. And in the big city, traffic emissions, namely, the vehicle exhaust is one of the main sources of suspended particles in the air.This study takes the west campus of Huazhong University of Science and Technology as the object. The meteorological data and particulate pollution situation is studied by two years of long-term fixed-point monitoring and a year of mobile measurement of particulate pollutants in the west campus of Huazhong University of Science and Technology. Then, the spatial and temporal diffusion characteristics of particulate pollutant and its influencing factors, especially the impact of vehicle exhaust pollution of the traffic on the main road off campus on the particulate pollutants in the west campus are analyzed by statistical analysis. In view of the fact that the bad ventilation is the important reason of haze, this study also uses numerical simulation method to study the effect of the layout of buildings on the wind environment of the block, and on the spatial and temporal diffusion characteristics of particulate pollutant. Therefore, some suggestions can be provided for campus ventilation design in the future so as to avoid and reduce the harm of vehicle exhaust pollution of the traffic on the main road off campus to the campus environment.The mobile measurement of particulate pollutants shows that traffic emission is one of the important sources of the particulate pollutant on and around the main road. In addition, among the particulate matters of traffic emissions, PM1.0 and PM2.5 is easier to diffuse than PM10.The ventilation in the block can reduce the pollution caused by local pollution sources and the increase of wind speed is in favor of the diffusion of particulate pollutant. Besides, the high plant density may lead to poor ventilation, and then hinder the diffusion of particulate matter concentration.The long-term fixed-point monitoring of particulate pollutants shows that the environment of the campus of Huazhong University of Science and Technology is jeopardized by the particulate pollutants seriously in the past two years, during which January was the most serious. This result is similar with the overall pollution status of Wuhan. Besides, the correlation coefficient of PM1.0, PM2.5 and PM10 is higher than 0.9. The concentration of PM1.0, PM2.5 and PM10 is almost not correlated with humidity, but it is negatively correlated with the temperature, which is consistent with the seasonal variation of the concentration. The hourly variation trend of PM1.0, PM2.5 and PM10 is correlated with the traffic flow. When the traffic is heavy, the proportion of the smaller particulate pollutants is higher. Furthermore, the higher wind speed can reduce the level of particulate pollution in the area. The concentrations of PM1.0, PM2.5 and PM10 show a high degree of negative correlation with the outdoor visibility.The numerical simulation shows that the wind speed is the most important factor that influences the diffusion of pollutants in the block, and the high wind speed is good for the quick diffusion of pollutants. When there is a certain angle between the direction of building and the direction of wind, it is conducive to the spread of pollutants in the block. However, in order to facilitate natural ventilation, the existing building standards require the buildings to face the dominant wind direction. Thus, the balance point between them should be reached and this paper finds out that 22.5deg to 45 deg is appropriate. The building layout that is high in the middle and low in the around is more conducive to the spread of pollutants, while the building layout that is low in the middle and high in the around is disadvantages to the spread of pollutants.All in all, traffic emission is an important source of particulate pollutants, having a great impact on the concentration distribution of the surrounding particles. Therefore, the spatial and temporal diffusion characteristics of particulate pollutant caused by traffic as well as its contributing factors should be studied to improve and control its pollution.