Numerical Analysis Of Reactive Pollutant Dispersion In An Urban Street Canyon

In this period of rapid urbanization, the raise of large city’s high-risebuildings amount and vehicle population easily leads to automobileexhaust gathering in so-called―street canyons‖which forms severepollution, so that investigation into the reactive pollutant dispersion in anurban street canyon has a positive significance. CFD method is used tomodel a symmetrical street canyon with H/W ratio of1. Thecharacteristics of the dispersion of reactive pollutant is simulated andanalyzed considering photochemical reaction in sunshine.Two terms of wind tunnel experiments data are used to validate thestreet canyon model set up in this study and it shows approving results.Two different chemical reaction mechanisms are used in this study. Usinga simplified NO-NO₂-O₃chemical reaction mechanism, the air flow fieldand pollutants concentration field in street canyon are calculated withvarious simulation parameters by changing exhaust intensity, bottomheating and upper wind velocity. The concentration variation tendenciesof two significant products in photochemical smog, O₃and PAN, are investigated using a more completed mechanism CBM-IV. Simulationresults show that O₃and PAN concentrations decrease when NO/NO₂ratio rises as they increase when VOCs concentration rises. The resultsalso tell that O₃concentration mainly depends on NO/NO₂while PANconcentration is more influenced by the amount of VOCs. O₃and PANconcentrations with different sunlight intensities are also calculatedshowing that O₃and PAN both increase with stronger solar energy.