Contaminants are ever-present in the air. Contaminated air entering a Gas Turbine will damage internal components and bring about a reduction in overall efficiency. The amount of contaminant entering a Gas Turbine, therefore, needs to be minimised. This paper describes recent developments in the understanding of one such contaminant, salt. It describes how salt is produced, how it varies climatically and how it varies from location to location and is presented here in the context of the author’s particular field of competence — air filtration system design. Salt ingestion by a Gas Turbine intake can cause corrosion and, given time, can accumulate on the compressor blades and reduce the aerodynamic efficiency. The removal of salt in the air is therefore of primary concern to all those involved in the design and operation of Gas Turbines. Salt removal systems are manufactured in various guises. The concept, however, remains the same — salt capture upstream of the Compressor stage. The drawback to this method of salt removal is that it results in a decrease in air pressure entering the Compressor and will consequently bring about a decrease in the overall system performance. As the requirement to remove more and more salt contaminant increases, the pressure drop across the method of filtration required to achieve this, increases. The responsibility of the Filtration Engineer is therefore to fully understand the requirements of the Gas Turbine, to understand the balance between pressure drop, salt removal and salt size and, consequently, to design an appropriate filtration system — one fit for purpose. Gas Turbines in the marine environment are generally found at heights less than 50m above sea level. It is this environment (the Marine Boundary Layer) which historically has been difficult to fully quantify. Herein lies the problem for those involved — if the environment is not fully understood how can the proper exploitation of the technologies be achieved? Recent developments, however, have led to a better understanding of salt in the Marine Boundary Layer. This paper describes these recent developments.