Investigation of PM2.5 Dispersion in Din Daeng District, Bangkok, Using Computational Fluid Dynamics Modeling

Din Daeng is a small and densely populated district of Bangkok, with two major expressways and three main roads in the area. PM2.5 concentration in Din Daeng district often exceeds both the daily and annual standards of the National Ambient Air Quality Standards. Computational Fluid Dynamics (CFD) was applied to investigate the effects of the metropolitan characteristics and traffic volumes on the dispersion of PM2.5. The turbulent flow was analysed using the Standard k-ε model. There were two scenarios in this simulation study. One was to investigate the consequences of having the expressways. The other was to examine the influence of the city lockdown due to the COVID-19 pandemic. The presence of the expressways in Din Daeng district was demonstrated to increase PM2.5 concentrations by approximately 3.4 times compared to the case without the expressways. In addition, the city lockdown substantially reduced PM2.5 concentration by almost 49% compared to that during the normal period. © 2023, Chulalongkorn University, Faculty of Fine and Applied Arts. All rights reserved.

Prediction of PM2.5 Dispersion in Bangkok Pathumwan District) Using CFD Modeling

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 PM2.5 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-epsilon 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 PM2.5 injection and dispersion. The concentrations of PM2.5 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 PM2.5 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 PM2.5 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 PM2.5 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 PM2.5.