Analysis Of Vehicle Exhausts Emission Dispersion And Influence On The Pedestrian In Urban Street

Accompany with development of urban motorization, the aggravation of traffic congestion in urban area brings negative effects on environment and human health. Environment pollution has become the most important problem faced by the large cities all over the world. Walking is one of the most important modes in travel, and urban street area is the important environment for pedestrian walking. Because of the large number buildings and vehicles in urban street environment, the vehicle exhaust pollutants are easy to accumulating and hard to dispersing, therefore the pollutant concentration in urban streets environment is higher than other areas. Pedestrians which walk and expose in air pollutants directly are the group who faces the most serious health risk.The thesis selected three important air pollutants (Nitrogen oxide, Carbon monoxide and Ozone) which had negative effects on human health, analyzed the definition and characteristics of pedestrian pollutants exposure and the influence factors of pedestrian walking speed, measured and collected the vehicle exhaust data by using on-board emissions measurement system, evaluated the precision of the different kind of vehicle exhaust models. Through collecting the traffic data, air pollution data and meteorologic data, analyzed the pollutant dispersion in urban area, built a platform which could simulate the pedestrian exposure condition in urban street area. The results of this thesis are as the following:(1) The thesis analyzed and compared the principle, vehicle type classification and application scope of three typical vehicle emission models (MOBILE, IVE and CMEM), collected the vehicle driving cycle data, exhaust emission data and fuel consumption data, compared the simulation results by different models with measured data. The thesis selected three kind of driving cycle fragment data (Cold Start, Hot Start and Stabilized) and input to CMEM model. The result showed that the microscopic emission model CMEM simulation precision was better than other macroscopic emission models.(2) The thesis improved the CALINE4 model by measuring the composition of the NO_X (NO₂+NO)in vehicle exhaust and the regression model of the NO_X and NO₂ relationship in urban street environment. The improved CALINE4 model can be used to simulation the concentration of CO and NO_X in urban street environment. Comparison between measured and simulated results showed that in the condition of the windspeed lower than 3.0m/s, the simulated results closed to the measured result. If the windspeed higher than 4.0m/s, the simulated results were lower than the measured results.(3) The thesis analyzed the correlation between the O₃ concentration and solar radiation, NO_X concentration, environment temperature, number of vehicle, wind speed. The correlation analysis results showed that there was a positive relation between O₃ concentration and windspeed. Accompany with the increasing of windspeed, the air pollutants mixing degree increases and the O3 formation reaction was accelerating. The multiple linear regression models for calculating O3 concentration in roadside and background were built. The comparison between measured and simulated results showed that the relative error of the roadside model was 7.71 %, and the background model was 4.08%.(4) The thesis built a simulation platform for the pedestrian air pollutants exposure research which could simulate the exposure by different signal control methods and different walking routes. The simulation platform comprised by five different function modules: Basic data collection module, Vehicle emission module (CMEM), Pollutants dispersion module (CALINE4 and Multiple linear regression models) and Pedestrian exposure calculation module. According to the different vehicle type classification definition in functions modules, the vehicle type mapping relation between different modules was built.(5) The thesis analyzed the traffic operation status, concentration of the pollutants, pedestrian exposure and pollutant inhaled dose in fixed timing signal and actuated signal by using the simulation platform. The simulation results showed that traffic operation status and concentration of the pollutants improved significantly, the value of pollutant exposure and dose decreased in condition of actuated signal. For example, the concentration of the CO decreased about 26.2%, the average value of the pedestrian CO dose decreased about 3.1ml.