Identifying ammonia non-slip conditions in a selective catalytic reduction application

A system comprising:

• a sampling module that samples first and second signals that indicate an amount of nitrogen oxides (NOx) upstream and downstream from a selective catalytic reduction (SCR) catalyst, respectively, wherein the second signal further indicates an amount of ammonia downstream from the SCR catalyst when ammonia is released from the SCR catalyst;
• a correlation determination module that determines an amount of correlation between the first and second signals, wherein the amount of correlation indicates a probability that ammonia is released from the SCR catalyst;
• a control module that determines an amount of ammonia stored in the SCR catalyst based on the amount of correlation between the first and second signals;
• and
• an injector control module that controls an amount of reducing agent injected into the exhaust gas upstream from the SCR catalyst based on the amount of correlation.