Most salts are hygroscopic. Try putting a mound of salt out on a table or countertop. Wait a few days and see how the salt clumps togeher. What has happened is that water vapor molecules stuck to the salt crystals making them "sticky" for each other. Eventrually, enough water would have been collected to partially change phase from gas to liquid and dissolve some of the salt, gluing the salt into one big solid mass. This dissolution of the salt by having the stuck vapor molecules turn into liquid water is the deliquescence step show below.

The droplet resulting from the deliquescence is very salty. The salt in solution binds the water molecules together, preventing many from junping off and evaporating. Because of the difficulty in getting these salty drops to evaporate, the environmental relative humidity can be as low as 75% before they start evaporating.

These droplets are called haze droplets and form the whitish haze that is often observed in the air around coastal and lakeshore towns. The high salt particle concentration coupled with the relatively high RH allow these droplets to persist.

Haze droplets are extremely small---aerosol particle size, or around 1 micrometer or less (a typical cloud droplet is at least 5-10 micrometers diameter, usually much larger). Small particles or droplets llike these obstruct visibility, but not as much as a thicker fog.