1.1 ,Practice D7897 applies to simulation of the effects of field exposure on the solar reflectance and thermal emittance of roof surface materials including but not limited to field-applied coatings, factory-applied coatings, single-ply membranes, modified bitumen products, shingles, tiles, and metal products. The solar reflectance and thermal emittance of roof surfacing materials can be changed by exposure to the outdoor environment. These changes are caused by three factors: deposition and retention of airborne pollutants, microbiological growth, and changes in physical or chemical properties. This practice applies to simulation of changes in solar reflectance and thermal emittance induced by deposition and retention of airborne pollutants and, to a limited extent, changes caused by microbiological growth.