A method (and a system that executes the method) for control of at least one sectional ammonia coverage degree profile NH3_profile for at least one SCR catalyst included in an exhaust gas treatment system, the method includes determining at least one ammonia sectional coverage degree profile NH3_profile_det for the at least one SCR catalyst based on a flow F, a temperature T and a composition C of the exhaust stream upstream of the at least one SCR catalyst. The method also includes comparing the at least one sectional ammonia coverage NH3_profile_ref with at least one sectional reference profile for an ammonia coverage degree NH3_profile_ref for the at least one SCR catalyst. The method further includes controlling, based on the comparison, at least one of a concentration of nitrogen oxides CNOX in the exhaust stream to be output from the combustion engine and a dosage of a reductant including ammonia NH3 to be injected into the exhaust stream upstream of the at least one SCR catalyst.