Air quality overview: North Cascades National Park Complex

Cummings, Tonnie

The report provides a summary and synthesis of air quality monitoring and air pollution effects research that has taken place in North Cascades National Park Complex. North Cascades National Park Complex, located in Northwest Washington, includes North Cascades National Park and Lake Chelan and Ross Lake National Recreation Areas. North Cascades National Park is designated as a Class I air quality area and is afforded special protection under the federal Clean Air Act. North Cascades National Park Complex is vulnerable to air pollution from nearby urban and agricultural areas, as well as to pollution from regional and even global sources. To better understand and protect air quality, the National Park Service has monitored air quality and air pollution-sensitive resources in the park since 1984. In 1994, the National Park Service Air Resources Division published a comprehensive review of the status of air quality and air pollution effects in five Class I parks in the Pacific Northwest. This report provides an update on air quality-related research and monitoring that has taken place at North Cascades National Park Complex. Park air quality is currently in compliance with all the National Ambient Air Quality Standards, but these standards do not provide adequate benchmarks for assessing ecosystem condition. The National Park Service Air Resources Division has, therefore, adopted the goal of natural conditions for assessing visibility impairment and uses ecological thresholds from the scientific literature to assess potential effects from ozone and deposition of nitrogen, sulfur and toxic air pollutants. Current average visibility at North Cascades National Park is about 34 percent hazier than natural conditions, with no significant improvement or degradation from 2000-2009. Currently, about half the visibility impairment at the park is due to sulfate particles in the atmosphere resulting from sulfur dioxide emissions from power plants and other sources. Under natural conditions, the contribution to visibility impairment from sulfate would be less than 25 percent. Nitrate concentration in precipitation decreased significantly at the park from 2000-2009. There was also a decrease in wet ammonium concentration. While there was no trend in 2000-2009 for sulfate, longer-term data (1987-2009) indicate a decrease in wet sulfate deposition at the park. Less than 10 percent of the nitrogen, and less than 5 percent of the sulfur, is in the form of dry deposition. Sensitive park ecosystems are considered at high risk for both acidification and nitrogen enrichment. Critical loads for sulfur have not been developed, but nitrogen deposition at North Cascades National Park Complex appears to be below critical levels shown to affect lichen communities. Efforts are underway to determine nitrogen critical loads for other ecosystem components. Ozone concentrations are below levels thought to be harmful to human health or vegetation; however, ozone concentrations increased slightly from 1996 until monitoring was discontinued in 2007. Elevated concentrations of toxic air pollutants have been detected in the park, including concentrations of some pollutants, such as mercury in fish, which exceeded wildlife or human health thresholds. Ongoing studies are investigating the extent of mercury contamination.

Air quality overview: North Cascades National Park Complex

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