This presentation summarizes the range of air pollutants that affect mountain ranges in North America, with a focus on the Rocky Mountains, the Sierra Nevada, the Cascades, and the Coast Ranges of both the U.S. and Canada. Regional air pollutants of interest include visibility-reducing particles, deposition of nitrogen and sulfur compounds, and ozone. Global air pollutants that affect mountain ecology include greenhouse gases, ozone-depleting substances and air toxics, such as mercury and persistent organic pollutants. The air pollution threats to species, biogeochemical processes, and human health range from severe in the southern coastal mountains of the U.S. to low in parts of the Sierra Nevada, Cascades, and northern Rockies. Many of these mountain basins include populations of sensitive lakes, streams, and watersheds with low acid-neutralizing capacities (less than 50 ueq/l) that can respond to deposition of nutrients and contaminants. Deteriorating visibility has been measured in all of these ranges, with contributions from fossil-fuel burning, agriculture, and forest and agricultural burning. These particles also play a role in climate change and human health effects. Emerging air pollution issues in the western mountains include elevated concentrations of persistent organic pollutants in snowpacks, the influence of climate change on air pollution and deposition, and the effect of prescribed fire on air quality.