The Research Of Urban Underground Tunnel Pollutants Emission Based On Traffic Charactirisic

In order to relieve traffic pressure of urban center and shorten the travel time, urban tunnels are becoming important topic for traffic development in large and middle-sized cities.Because of the relatively enclosed space of urban tunnels, vehicle pollutants are difficult to spread and discharge out of tunnels. Thus mechanical ventilation are required to dilute vehicle pollutants through vertical shafts or tunnel exits, and it could keep pollutants concentrations under a safety threshold. Calculating vehicle emissions scientifically plays an important role to determine the quantity of air flow necessary in the tunnel. Vehicle emission is depended on vehicle emission factors, which are expressed as the amount of species emitted per vehicle driven distance.Vehicle emission factors are dynamic parameters,which depend on many variables such as automotive engine performance, roadway conditions and traffic characteristics. Urban tunnels just appear in China in recent years, and the related researches are still at an elementary stage and lack of basic data. The ventilation design standards and parameters of urban tunnel are mainly refered to Chinese Guidelines for Design of Ventilation of Highway Tunnels or European countries related design specifications.Compared with highway tunnels, urban tunnels have great differences in structure, traffic characteristics(traffic volume, vehicle speed, vehicle type, fuel type etc) and functions. Additionally, characteristics of urban transport and vehicle emission change greatly in relation to rapid development of China’s economy and engine technology, continual improvement of fuel quality and roadway condition and strict regulation of vehicle emission standard.This study analyze factors of vehicle emission, carbon monoxide(CO) and nitrogen oxides(NOx) are taken as the environmental control indexes for mechanical ventilation. To obtain the vehicle emission factors with current roadway conditions and traffic characteristics, measurements of CO and NOxare conducted with a mixed vehicle fleet and calculated in-use fleet average emission factors in three tunnels from 2012 to 2014. Shanghai East Yan’an Road tunnel, Yingpan Road tnnnel and Changsha Yingpan Road tunnel are chose as typical representatives for Chinese urban tunnels, as two of them are old urban straight tunnels and the other one is a newly built urban tunnel with interchange ramps. In this paper, vehicle emission levelsunder current roadway conditions and emission characteristics of urban tunnels are obtain. The article further put forwarddynamic correction method for vehicle emission factorbased on the actual tunnel in order to achieve dynamic monitoring of the underground road emission factor and realize the energy saving operation of the tunnel ventilation system.The results will provide meaningful reference for ventilation design and environmental assessment of urban tunnel, and further help provide basic data to formulate relevant standards and norms.