The CO concentration is an important parameter for design of ventilation systems in enclosed parking lots. By using the initial estimation of CO concentration and investigating the CO removal effectiveness, the ventilation system with low energy consumption and high indoor air quality could be designed. In this paper, by using the principle of mass conservation and the definition of CO removal effectiveness, an analytical relation for estimation of CO concentration is obtained. This relation is estimate the variation of CO with time by using the main functional parameters of parking lot. In spite to the physics of flow, the increasing of air quality is obtained by reducing the idle cars and the mass flow rate of CO exhausted from this cars and increasing the parking lot volume and the ventilation flow. This trend is consistent with the proposed relation of this paper and so the results of this paper could be used as the criteria for estimation of CO concentration and enhancement of ventilation system design. The comparison between results of the proposed relation and experimental and numerical results are represents good accuracy of proposed relation. Furthermore, the amount of energy reduction by enhancing the flow pattern is expressed by using the proposed relation of this paper. In the last section, the approach of different standards is expressed and the modifying suggestions for enhancement of them are expressed.