The Impact of Air Pollution on Stone Materials

Air pollution can have a significant impact on stone materials used in monuments, buildings, and sculptures. Sulfur and nitrogen oxides are particularly harmful pollutants, especially in carbonate stones. These oxides, reacting with moisture in the air, result in the formation of acids able to erode the stone surface and gradually compromise its structural integrity. The acids can also combine with airborne particulate matter, heavy metals, and salts, leading to the development of black crusts. These not only have detrimental effects on the stone's integrity but also affect the original appearance of the surfaces, threatening the conservation of important monuments and buildings. This review discusses the characteristics of black crusts and their relation to the environment and stone materials.