Air pollution, both indoor and outdoor, has been found to be related to serious adverse health effects. Accurate estimation of air pollution exposure has become very important to suggest proper air pollution control policies and to further assess the effectiveness of these policies. In many instances, personal exposures have been found to be greater than concentrations measured at fixed site monitoring stations. As people spend most of their time indoors particularly during harsh weather conditions, it is necessary to consider indoor air quality in exposure assessment studies. The current paper focuses on the importance of personal exposure assessment based on spatial and temporal activity patters both indoors and outdoors.