| As a result of the increase in vehicle population,the growth in road traffic and the rapid economic growth,air pollution related with traffic exhaust is getting worse in Chengdu urban area. To better understand the vehicle emissions in Chengdu urban area and recommend effective vehicle emission control policy for the city, vehicle population, traffic flow on roads and distribution of the types of vehicles are investigated. Based on the pollution sources and meteorological conditions of Chengdu in 2007 CALPUFF model, a multi-layer, multi-species non-steady-state puff dispersion model was used to simulate pollutants dispersion of vehicle emission, estimating the influence of vehicle emission to air quality quantitative. The results were summarized as follows:Vehicle population in Chengdu city in 2007 is 177.95×104, and there are 66.03×104 in urban area, take a proportion of 37.1%. The population of Motorcycles and passenger car is 93.8×104 and 72.5×104, taking a part of 52.69% and 40.72%. The survey results showed that passenger car, taxi, bus, truck and motorcycle accounted for, 73.2%, 16.6% and 2.6%, 5.5% and2.2% of the total traffic volume. The total emissions of CO, NOx and HC from vehicles in urban area in 2007 were 16.7×104t, 1.77×104t and 1.38×104t. CO, NOx and HC emission from vehicles contributed 79.3%, 43.1% and 31.1% to total emissions. Vehicle is the main source of NO2 and CO in urban area; the concentration contribution rate of NO2 and CO is 74.5% and 93.7%.In respect that the special characteristic of concentration of vehicle emission had a relationship of traffic flow and dominant wind direction, area of high value were in or around erhuanlu. As an influence of dominant wind direction, area of high value had an excursion to southwest.
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