A cooling system circulates cooling air through information technology (IT) modules within a large scale information handling system (IHS). An air handling unit (AHU) directs cooling air through an IT module. The AHU is in communication with a controller. The controller is also in communication with an ambient condition interface to determine a level of a contaminant in outside air. The controller further: determines whether the level of the contaminant exceeds a threshold; and in response to determining that the level of the contaminant exceeds the threshold, configures the AHU to perform a mechanical cooling mode that excludes the outside air by recirculating air within an IT module via the AHU. In response to the level of contaminants not exceeding the threshold and other detected ambient conditions are favorable to using outside air to cool the IHS, the controller configures the AHU to use outside air.