How does the chemical composition of marble influence its interaction with pollutants?

Marble, a metamorphic rock composed predominantly of calcite (calcium carbonate, CaCO₃), interacts with pollutants in ways heavily influenced by its chemical composition. When exposed to acidic pollutants like sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) from industrial emissions or acid rain, the calcite in marble undergoes a chemical reaction. This reaction dissolves the calcium carbonate, forming gypsum or other soluble salts, which weakens the stone's structure and leads to surface erosion, pitting, and loss of detail—a process known as marble weathering.

Additionally, particulate matter and soot can adhere to marble surfaces, further accelerating degradation by trapping moisture and acidic compounds. The porosity and mineral impurities in marble also play a role; higher porosity allows deeper pollutant penetration, while impurities like clay minerals may react differently, altering deterioration patterns.

Understanding these interactions is crucial for preserving historical monuments and managing urban pollution impacts on architectural marble. Mitigation strategies, such as protective coatings and pollution control, can help reduce damage caused by these chemical reactions.