Define the Predominant factor in atmospheric corrosion?

The predominant factor in atmospheric corrosion in areas located above splash zone is moisture as there is an excess availability of oxygen.  In the part of steel member, located above water line but within the splash zone, corrosion is accelerated by water / salt water and the effect of wetting and drying cycles.  The predominant cause of corrosion in the submerged portion of steel member is the concentration of dissolved oxygen.  The predominant causes of corrosion in the part of steel structures that are below the mud line are electrical conductivity, total acidity, water contamination, and dissimilar metals.