Air Pollution

The foliage of trees, particularly hardwoods, is very susceptible to air pollutants including sulfur dioxide, fluorides, and oxidants such as ozone. These pollutants can be absorbed by leaf tissues, and if concentrations are high enough, will kill cells in a few hours or days. This can stress trees and lower overall tree health. Well defined concentration gradients of pollutants may exist downwind of pollution point sources, and in these cases, injury is most severe near the pollution source and will diminish as distance from the source increases. In other cases, regional sources of these pollutants can result in uniform and widespread distribution of air pollutants over large geographical areas. In broadleaf species, ozone damage will cause leaf stippling or unusual pigmentation patterns. The stippling may be red, purple, brown, or black, and can be restricted to certain areas of the leaf or appear uniformly over the entire leaf surface. Ozone can cause chlorotic mottling and tip burn in conifers. Sulfur and fluoride injury usually results in interveinal and/or marginal necrosis of leaf tissue.