Anyway got off topic it is the acid in the rain reacting with the marble and producing gas possibly other stuff as well as i said can t remember thus it looks as though the marble is changing physically i m sure a google search of the make up of marble and acid rain and the possible reactions of the molecules will give you your answer.
Is acid rain damaging a marble statue a physical change.
How does acid precipitation affect marble and limestone buildings.
When sulfurous sulfuric and nitric acids in polluted air react with the calcite in marble and limestone the calcite dissolves.
When sulfurous sulfuric and nitric acids in polluted air and rain react with the calcite in marble and limestone the calcite dissolves.
Acid rain damaging a marble statue is a physical change.
Over decades of exposure to acid rain the details of a statue can be lost slowly turning them into featureless blobs.
Acid precipitation affects stone primarily in two ways.
Although metal statues resist physical deterioration from acid rain better than stone they can develop discoloration and streaking.
In exposed areas of buildings and statues we see roughened surfaces removal of material and loss of carved details.
In exposed areas of buildings and statues we see roughened.
Stone surface material may be lost all over or only in spots that are more reactive.
Acid rain will wear away and destroy the outer layers of the marble.