Once formed, the ozone reacts again with the hydrocarbons to form a group of very reactive compounds called peroxides. Sometimes these reactions occur directly in the leaves of plants where the hydrocarbons changed are a class of plant hormones called auxins. Pollution-associated plant damage has been specifically traced to these altered auxins. These are most visible to an observer looking down from an elevated location. Usually spruce hold needles for five to seven years before dropping them These years can be counted by the nodes that ring the branches every few inches.
Damaged trees drop their needles early and flower more profusely.
Flowering is also affected in deciduous trees. In addition the leaves are smaller, and the pattern of branching is changed. Also certain changes in the biochemical composition of conifer foliage can reflect air pollution damage. We found some of these changes in the needles from near Fairbanks and Seward. Needles from the yellowed trees near Minto Flats were not analyzed.