Nowadays, lack of space in city center has forced the architects a propose a vertical construction to provide public facility, including the parking garage. Generally, this vertical parking garage has enclosed environment condition, which could be constructed under the building or in the middle of other buildings. This environment causes the parking garage will not have an adequate fresh air circulation or air change rate and gives a more risk due to the accumulation of air pollutants which is emitted from the cars inside. In this research, it observes a simple enclosed parking garage which normally can accommodate six cars. The air pollutant, particularly Carbon Monoxide (CO), from three gasoline cars is extracted by an exhaust fan in a proper location. Two location of exhaust fan are proposed to investigate better air circulation and better air pollutant extraction from the parking garage. The first option (Position of A) installs the exhaust fan near to the parking space units and the other installs the exhaust fan near to the pathway. Each option will follow two worst condition of simulations which are predicted will give a significant impact to Indoor Air Quality (IAQ). Each simulation has to extract the emission from three idle cars with same rate of air circulation of six air change per hour. The results show the influence of air flow pattern to the dispersion of air pollutant. An adequate air flow near to the emission source will cause the increase the maximum of air pollutant concentration. On the other hand, it can minimize the spread of air pollutant dispersion.