Study Of Fluence On The Building Downwash On City Tunnel Efflux Of Pollutants Diffusion

As the traffic pressure increased in our country, urban tunnel plays a more and more important role in traffic system, at the same time, concentrative pollutant emission at the tunnel portal also causes regional air pollution. So this paper researches building downwash influence on city tunnel pollutant distribution and diffusion law. It is very important for urban environmental protection work, and also provides theoretical basis for the pollutant discharge of the tunnel portals.Taking a city tunnel under road as engineering background, the paper uses the AERMOD-model to study building downwash influence on the pollutant distribution and diffusion of the tunnel portals, in the presence of building parameter or not, respectively. It uses the local ground meteorological data (including the atmospheric temperature, humidity, wind direction, wind speed, total cloud cover and low cloud cover), terrain data and sounding data parameters.Results show that any building downwash presents significant difference under the different wind direction and wind speed. Different wind direction makes different swirling down the street, which leads to significant difference of pollutants diffusion trend. And under the same wind direction, wind speed strengthenes the building downwash effect. And under the same wind speed, the building downwash presents decrease first and then increased trends with the increase of forecast height. When the wind speed is very small, any building downwash has smaller influence on distribution of pollutant. Analyzing the pollutant dispersion of 1.5m high found that, two group data maximal ratio of the same grid is 7.28 in building area, and the difference between two group data is not big in no buildings. Only extending the building height found that the pollution concentration value is 0.98-5.64 times of the original building height.Through the study found that, the pollutant will accumulate in a local area near the pollution source, while the diffusion condition on both sides of the tunnel is very well, and to the building area it can meet the requirements of environmental air quality standard limits and doesn’t affect the residential living environment.