Method 518.2 is the Acidic Atmosphere test from MIL-STD-810H. Section 518.1 (Purpose) states that the acidic atmosphere test is used to determine the resistance of materials and protective coatings to corrosive atmospheres, and when necessary, to determine its effect on operational capabilities.
The test exposes materiel to a controlled acidic environment to evaluate the degradation of materials, coatings, and finishes when subjected to industrial pollution and acid rain conditions.
This method is important for evaluating military equipment that may be deployed in or near industrial areas or environments where acidic atmospheric conditions are prevalent.