Lichen data are being collected in western Oregon, Washington and southeastern Alaska to aid decision-making processes that affect air quality on national forests. Common lichens are analyzed for tissue concentrations of pollutants such as sulfur, nitrogen, lead, and metals. To identify geographic areas of concern and assess the significance of trends over time, forest managers must be able to distinguish elevated values from values typical of background sites. To determine background ranges, tissue data from 8 national forests were compared after removing sites close to urban areas, roads and high human activity. Ranges of anthropogenic elements in southeastern Alaska were similar to OR and WA Forests. The 97.5% quantiles of the combined “clean sites” database were used as cut-offs for elevated values. All values were then mapped. Elevated values for sulfur and nitrogen were observed along the Columbia River Gorge National Scenic area (CRGNSA), the northern half of the Mt. Hood National Forest, the I-5 corridor, urban areas and near national forest boundaries. Lead was highest in urban areas, the CRGNSA and along the crest of the Cascade Range. Other metals were elevated in the CRGNSA, in urban areas, in areas with serpentine soils on the Umpqua National Forest, and in the north half of the Gifford Pinchot National Forest corresponding to areas of greatest ash deposits from Mt. St. Helens eruptions. A next step is to determine whether adverse effects on forest health, community composition or ecological function can be detected in areas where natural events or conditions cannot explain elevated values.

Key words: air pollution, lichens, metals, nitrogen, Pacific Northwest, sulfur