Pollutant Source Symptoms Ozone Nitrogen dioxide and Four different kinds of hydrocarbons emitted from symptoms can result from automobiles, industrial ozone exposure. The most combustion, oil refineries common symptom is localized and many lesser sources thickening and pigmentation react with sunlight to of the cell walls causing form ozone. During sharply defined small dot- electrical storms, ozone like lesions. General is produced and can be upper surface bleaching is brought down from the another common type of upper atmosphere by injury. Large bifacial strong down drafts.
Some species show only general chlorosis or chlorotic mottling or chlorotic flecks.
Sulfur Dioxide Emitted during combustion Accumulation of sulfite of many fuels, especially in tissues produces a coal and petroleum. Also general chlorotic appear- released during smelting ance of the leaf and a operations. The necrotic areas may fall out and after much of the leaf is affected, it will shed. First sign of injury is a dull-green watersoaked discoloration of these tissues within 24 hours or several days depending on concentration. These watersoaked tissues turn light to dark brown within 48 hours during hot weather.