Nanosecond-two-photon absorption laser induced fluorescence (ns-TALIF) technique was employed to investigate the transients of a strongly emissive pulsed microwave discharge. We analysed the conditions that have to be fulfilled in order to use the TALIF intensities measured with the laser central frequency tuned to the absorption peak instead of the fully integrated laser excitation spectrum absorption for measuring N-atom densities. We demonstrate the validity of the method in our conditions and applied it for the straight forward monitoring of N-atom densities during the transients of a pulsed ECR plasma. We especially demonstrated the existence of an unexpected increase in N(4S) atom density of about 10% at the early stage of the transition from high- to low-power phase. Using a self-consistent quasi-homogenous plasma model encompassing a detailed state-to-state kinetics, a thorough analysis of the N-atom and N2(B) kinetics was carried out and enabled attributing this enhancement to surface de-excitation of N(2D) and N(2P) atoms. The rise of the N(4S) atom density can serve as an indicator of the concentration of N(2D) and N(2P) atoms in the discharge.