Rate constants for collisional loss and transfer of population and rotational angular momentum alignment have been determined for the CN(A 2 Π, v = 4) + Ar system. Aligned samples of CN(A 2 Π, v = 4, F 1 , j = 1.5 -23.5 e) were prepared by optical pumping on the A-X(4,0) band. Their evolution was observed using Doppler-resolved Frequency-Modulated Spectroscopy in stimulated emission on the A-X(4,2) band. Stateresolved total population removal rate constants, and state-to-state rotational energy transfer (RET) rate constants, are found to be in excellent agreement with previous experimental measurements and theoretical predictions for the v = 3 level. Rapid elastic depolarization of rotational alignment was observed for j = 1.5 -6.5, with an average rate constant of 1.1 x 10 -10 cm 3 s -1. This declines with increasing j, reaching zero within experimental error for j = 23.5. The polarization transfer efficiency of the initially created alignment in state-to-state RET was also determined for the selected initial state j = 6.5, F 1 , e. Substantial depolarization of the alignment was observed for small ∆j transitions. Alignment transfer efficiencies ranged from 0.55 ± 0.06 for ∆j = -1, to 0.32 ± 0.08 for ∆j = +3. These measurements are discussed with reference to recent experimental and theoretical advances on collisional depolarization of related open-shell species. We suggest that the surprisingly efficient collisional depolarization observed may be the result of the multiple potential energy surfaces involved in this system.