The Impacts Of Ground Thermal Conditions And Block Density On Traffic Pollutant Dispersion

Environmental atmospheric problems, especially the impacts of aerosol particles on air quality, are receiving more and more concerns both in environment science and heating, ventilating and air conditioning (HVAC) field in recent years. The deterioration of outdoor air quality not only decreases the indoor air quality in natural ventilation rooms, but also leads to the reduction of fresh air volume. Meanwhile, traffic waste has been the main reason of air pollution in urban areas, therefore it is crucial to study the air quality around block buildings in street canyons.Thermodynamic condition plays a significant role in flow pattern and pollutant dispersion around block buildings within street canyons. The aerosol dispersion mechanism have been studied in the past dacade, but few were about the impacts of inner heat sources on particle dispersion and diffusion. In the present study, numerical simulating results are compared with the experimental data found in the literature and flow fields and concentration distributions in the street canyons are simulated and discussed according to different wind speeds, ground thermal conditions and block densities, and particle with diameter of 2.5μm is considered as a typical size.The results indicate that ground thermal conditions can greatly influence the pollutant dispersion in street canyons. However , the impacts decreases since the wind speed increases. Buoyancy force strengthens the upright traffic pollutant dispersion, thus the increasing ground heat flow would lead to the concentration decrease in breathing levels in the canyons, but the air quality in buildings along the cross roads high floor will be easily threatened. In addition, the impacts of ground thermal conditions on particle distribution can also be affected by main street width. The greater the width is, the smaller the impacts will be; the impacts would be overlooked when the width rises to a certain value.Block density along the streets shows little infection on the whole part of the flow pattern within the community. Since the building spacing can enhance the air exchange rate in the community, it benefits to build better air quality.