Regional conditions vary widely. When works of art are displayed or stored in or nearby a city, pollution from car exhaust and the burning of fossil fuel endangers them. In the tropics or near-tropics, high relative humidity, sunlight and mold pose threats.
Interior pollution must be considered as well. What will be the immediate surroundings? A new building, for example, with fresh paint and new concrete can be a dangerous place to install works of art, especially photographic prints. The frame can mitigate some of these dangers, but protecting works of art exposed in the world entails monitoring conditions and, if possible, controlling the environment outside the frame as well.
Works of art are especially vulnerable to light, relative humidity, heat, pollution and biological threats. When uncontrolled these factors act in concert. Mold, a biological threat, is everywhere. But only in conditions of high heat and high humidity does mold pose a serious hazard. Oxidation is a constant threat of damage to paper, and acidity in paper has long been a major cause of its disintegration. But high temperatures, high relative humidity, and atmospheric pollution, especially in combination, hasten the deterioration.