Prediction of PM_2.5 Dispersion in Bangkok Pathumwan District) Using CFD Modeling

Abstract

City configuration, meteorological conditions and emission source are the important factors affecting the dispersion and concentration of pollutants within urban street canyon. The dispersion of PM_2.5 emitted from traffic in Pathumwan district, Bangkok which has the characteristics of street canyon was predicted using a Computational Fluid Dynamics (CFD) model with the RANS standard k-ε turbulence model. The studied area covers the area with high aspect ratio such as the shopping center area with the skytrain structure. The Discrete Phase Model (DPM) was used for simulating the PM_2.5 injection and dispersion. The concentrations of PM_2.5 were investigated under different conditions to demonstrate the effects of skytrain structure in the street canyon, meteorological conditions, and city lockdown due to the COVID-19 pandemic on PM_2.5 concentration. The numerical model was validated with the measured data from the air quality monitoring station of the Environment Bureau, Bangkok. The reduction of emission rate during the city lockdown causes the PM_2.5 concentration to decrease by 1.35 times from the normal time. In addition, the city configuration with the skytrain structure located between the tall buildings results in higher PM_2.5 concentration than the case without the skytrain structure in Pathumwan district by around 1.2 times. Moreover, the meteorological conditions must be considered, especially wind speed and direction. Finally, the results obtained from the simulation will be used for proposing the guidelines to reduce the concentration of PM_2.5.