Systems, methods and apparatus disclosed that include an internal combustion engine and an exhaust system that includes an exhaust aftertreatment system with an SCR catalyst. A NOx sensor downstream of the SCR catalyst is provided along with techniques for estimating an amount of NOx and NH3 at the tailpipe to decouple the impact of cross-sensitivity of the NOx sensor to NOx and NH3. Feedback control of the reductant dosing amount based on these estimates is also provided.