Environment - Pollution
There are three specific kinds of pollutants which are most damaging to works of art.
· Sulfur oxides, particularly sulfur dioxide, SO2. They are generated by the burning of fossil fuels in power plants and boilers. Sulfur oxides ultimately form sulfuric acid. In combination with light SO2 is especially dangerous for paper and textiles. SO2 levels have been trending lower in recent decades in American cities, though not in many other parts of the world.
· Nitrogen oxides, especially NO2. They are generated by automobile exhaust. Like SO2, NO2 forms an acid in the presence of water, nitric acid, which is a strong acid and an oxidizing agent. These emissions have also dropped in US urban areas in recent years.
· Ozone. (O3). One of the effects of sunlight on car exhaust is the production of ozone - an element of photochemical smog. Ozone breaks chemical bonds in almost all organic materials. It is also a powerful oxidant, and a cause of fading of pigments and dyes. Ozone levels are also gradually trending lower.Glazing that blocks ultra-violet light is generally recommended, though it should be noted that even protected from UV, framed works are highly vulnerable to damage from sunlight. We now have access to non-reflective acrylic glazing. Its coating also renders it non-static, a decided advantage over conventional acrylic.
These three gases have always occurred naturally in our atmosphere. Despite some recent improvement though, combustion in automobiles and power plants is a far greater source. And these pollutants are most heavily concentrated in cities, where works of art are concentrated as well.
Within the closed environment of frames and display cases, pollutants can be especially damaging to works of art. Woods emit acids, especially tannic, formic and acetic acid. Composite wood materials such as plywood and particle boards also emit pollutants from glues. Off-gassing from wood finishes represents yet another source of interior pollution.
Particulate pollution, such as dust, soot, and dirt, poses another threat. Not only will particulates soil and abrade art materials, they form a welcoming environment for molds and other organisms.