ABSTRACT
This chapter demonstrates that air pollutants can have both long-term (chronic) and short-term (acute) effects on plants, which are economically significant. They also affect visual range by absorbing and scattering light, and they damage materials by chemical action. Mosses have no root system to take up minerals from the substrate on which they grow, and accumulate materials such as heavy metals from wet and dry deposition. For most plants, the guard cells open during the daytime to allow gas exchange for photosynthesis while the sun is up, and close at night to conserve water. The single most important impact of air pollutants on plants is to impair the functioning of the stomatal guard cells. Visual range has been considered a useful measure of urban air properties. It should also be noted that it is the effectiveness of the particulate form of the material, rather than its opacity or refractive index, that is mainly responsible for the reduction in visual range.
