A system for a virtual dew point sensor is disclosed including a method for operating the virtual dew point sensor. The method includes determining a first humidity ratio indicative of the humidity associated with an ambient air as a function of at least a relative humidity associated with the ambient air. The method also includes determining a second humidity ratio indicative of the humidity associated with an exhaust gas as a function of at least one engine parameter. The method also includes determining a third humidity ratio indicative of combustion air directed toward an inlet manifold of an engine as a function of the first and second humidity ratios. The method further includes determining at least one dew point indicative of the combustion air as a function of the third humidity ratio and a pressure indicative of the combustion air.