For a concrete cask dry storage system, the characteristics of chlorides deposited on the surface of the stainless steel canister can significantly affect the susceptibility against stress corrosion cracking (SCC). This paper presents the result of an in-depth investigation into chlorides in the marine atmosphere and the effects on dry storage canisters. Recently, a series of full-scale thermal experiment and computational fluid dynamics (CFD) simulation have been implemented for a dry storage system. The simulated flow temperature and velocity are used to determine the air buoyancy and aerodynamic drag acting. The forces are then used to further predict the movement of chloride particles with the gravity force. The flow velocity is finally related to the critical size of a chloride particle leaving the system. The result obtained agrees well with those of field measurement and canister inspection. In brief, chlorides in the marine atmosphere may deposit on the canister surface, but the deposition rate is small.