NUMERICAL STUDY OF AIR POLLUTANTS DISPERSION IN AN URBAN STREET CANYON
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IOE Pulchowk Campus
Abstract
The alarming increase of hazardous pollutants in South Asian cities such as Kathmandu,
Delhi, Mumbai, Dhaka, etc risks the life of every individual there. The situation worsens
especially, in the winter rising the air quality index to life-risking situations. A proper scientific study and modeling of the pollutants are necessary in order to manage the pollution level
properly. A major source in the production of such harmful pollutants is vehicles and industries. A Computational Fluid Dynamics (CFD) approach is proposed to model the pollutants
emitted by vehicles using different Reynolds Averaged Navier Stokes (RANS) turbulence
models in the street canyon setup. The primary aim of the study is to understand the effect of
turbulence on the transport of gaseous pollutants in the street canyon. This is accomplished
by developing a turbulent steady-state solver for the passive transport of pollutants. RNG
k − ε model performed best among other turbulence models with mean FB -0.105, NMSE
0.045, FAC2 0.915 and R 0.93 which is validated with the experimental data. An increase
in dispersion of pollutants by 51.4% for AR=0.2 and by 42.33% for AR=0.5 was observed
in comparison to AR=1. Street canyons with a low aspect ratio of 0.2 effectively assisted
the escape of pollutants. Higher aspect ratios result in flow fields that are more constrained
and stagnant, which restricts the dispersion of pollutants. Further, the balconied building
lowered the concentration of gaseous pollutants in specific regions only and reduced the exchange concentration flux of pollutants with atmospheric air above the street canyon. Higher
wind speeds allowed the concentration to disperse more effectively in Baghbazar’s street
canyon, resulting in lower concentrations of pollutants
Description
Air pollution is one of the major challenges humankind is facing in the 21st century. Rapid
urbanization, industrialization, increasing number of vehicles, etc are some of the problems
faced by the major cities which impact the lives of many people due to air pollution. The
air quality index (AQI), which measures the concentration of different elements of air pollution is increasing day by day