Influence of initial equilibration of NH3 and HNO3 on number of droplets activated during a cloud model simulation is studied. This is done with a size-resolved droplet box model including detailed microphysics and liquid phase thermodynamics. The results show that when both ammonia and nitric acid are present in the gas phase simultaneously, the number of activated droplets is dependent on the history of the air masses forming the cloud. Simulations show that in situations where the aerosol distribution is in equilibrium with condensable trace gases prior to cloud formation, the number of cloud droplets is lower than in the nonequilibrium situation.