Human exposure to street level air pollutants in Colombo and exploration of mitigation options using CFD modeling

Abstract

Human exposure to street level air pollutants in Colombo and exploration of mitigation potions using CFD modeling was studied. To fulfill the requirement, present study was designed to gather baseline air pollution data, health risk assessment data and computer modeling was subsequently applied to a selected urban area and urban school to minimize the air pollution. For the purpose of estimating the air quality effects of land use and planning variables, a free-ware model named ENVI-met was used. ENVI-met is a numerical, 4 dimensional (three spatial plus the time dimension) microclimate free ware model which can simulate the microclimate within street canyons through the solution of the physical basic equations for the wind current, the thermodynamics and the radiation balance of surfaces. In order to estimate the effect of land use and urban planning variables, several ENVI-met simulations were run: change of street vegetation, change of soil conditions and building geometry. Measured Respirable Particulate Matter (RPM) values were used to calibrate the simulation cases. It was found that the high risk urban location had RPM of 437~glm3 whereas low risk village had 212~glm3. Total Suspended particulate mater (TSP) levels during peak hours (7.30am-8.30am and 2.00pm- 3.00pm) exceeded the Sri Lankan standard (>538 ug/m ' against 500 ug/nr') ..The data also revealed that apart from the number of vehicles, meteorological factors such as high temperature and low relative humidity increased the Respirable Particulate. Matter. A significant different in aerosol exposure levels was resulted in urban and rural dwellers for S02 and N02. Similarly exposure levels of urban & rural school children were resulted for S02 and N02. Simulations carried out at the urban area and school area clearly showed that the increasing greenery and banning of vehicles from busy sub roads with paving resulted the decreasing of particulate matter concentration. On the other hand, high rising buildings resulted the increase of particulate matter concentration heavily in the urban area and urban school respectively. Compared to the Base Case, results have shown that marked decrease of PM concentration has occurred by the suggested Best Case and for the Worst Case considerable increase of PMIO concentration in the urban area and urban school respectively. Best city design with minimum air pollution can be modeled using the ENVI-met computer modeling software with minimum cost. Therefore possibility of using this model in planning stage of new cities as well as redesigning of cities is highlighted.