Study on mitigation of automobile exhaust pollution in an urban street canyon: Emission reduction and air cleaning street lamps

Affected by the rapid growth of the number of fuel motor vehicles, the automobile exhaust pollution in the street canyon is becoming more and more serious. Different from the pollution source control technology usually used for outdoor air pollution control, an air cleaning street lamp is designed in this work. A 3D steady numerical model with line source pollution is established to simulate the air flow and pollutant diffusion in street canyons and validated. Then, the distributions of pollutants in 90 scenarios of street canyons are numerically simulated. The results show that wind direction and wind speed have great influence on pollutants diffusion in street canyons. Air quality in street breathing zones is improved with the reduction of emission; however, the air quality inside the street canyon is still worse than that outside the street canyon. Scenario with air cleaning street lamps with four 45° downward air outlets is shown to work better in improving air quality. In most of the studied cases, air cleaning street lamps are found to be more effective than reducing emissions from automobiles. A better method to improve the air quality in street canyons is to combine emission reduction measures and air cleaning street lamps. For the high-pollution breathing zone under perpendicular, oblique and parallel approaching wind directions, by this better method the mean PM concentration decreases by 14.38%, 7.68% and 17.78%, respectively; the mean NO_x concentration decreases by 24.92%, 21.33% and 29.03%, respectively; the mean CO concentration decreases by 12.77%, 7.45% and 15.05%, respectively.