A computer simulation of some chem. scenarios are presented to obtain preliminary information on what can be learned from pump-and-probe lidar expts., i.e., in situ laser flash photolysis in the troposphere. The decay of the OH concn. following the flash photolysis by different spatially resolved techniques is done under different conditions where the significant chem. and meteorol. parameters were sep. measured, so that model calcs. can be compared with time-dependent OH concns. The scenarios, within the limits of the simplified chem. model, are only realistic for a static atm. without turbulence or diffusion, i.e., at short delays after the laser flash perturbation. Relaxation/recovery of the atm. species occurs on different time scales according to the strength of the perturbation or the species involved. Several transient species were detected during system recovery back to steady state.