Explore Air

Chiricahua National Monument Air Quality Information


Chiricahua National Monument, Arizona
Chiricahua National Monument (NM), located in southeastern Arizona, was established in 1924 to protect a unique area of dramatic rock spires, pinnacles, columns, and balanced rocks. The monument now encompasses 12,984 acres, with 10,290 acres of designated wilderness. As a consequence of the Clean Air Act Amendments of 1977, the Chiricahua National Monument Wilderness was named a Class I air quality area, receiving the highest protection under that Act. Because of its location at the intersection of the Chihuahuan and Sonoran deserts, and the southern Rocky Mountains and northern Sierra Madre in Mexico, the monument is an area of tremendous biological diversity.

Both local and distant air pollution sources affect air quality in Chiricahua NM. Power plants, smelters, and other sources in Pima, Pinal, and Cochise counties in Arizona, and Hidalgo County in New Mexico, all contribute pollutants to the monument. In addition, pollutants from power plants, smelters, and other sources in Mexico affect the area.

The air quality related values (AQRVs) of Chiricahua NM are those resources that are potentially sensitive to air pollution, and include vegetation, wildlife, water quality, soils, and visibility. At present, visibility has been identified as the most sensitive AQRV in the monument; other AQRVs may also be very sensitive, but have not been sufficiently studied. Although visibility in the monument is still superior to that in many parts of the country, visibility in the monument is often impaired by light-scattering pollutants (haze).

The U.S. Environmental Protection Agency’s Regional Haze regulations require States to establish goals for each Class I air quality area to improve visibility on the haziest days and ensure no degradation occurs on the clearest days. As part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, visual air quality in Chiricahua NM has been monitored using an aerosol sampler (1988-present), a transmissometer (1989-present), and a 35mm camera (1981-1995). An analysis of 1990-1999 data indicates that visibility in Chiricahua NM is improving on the clearest days and degrading on the haziest days.

Surface waters in Chiricahua NM are generally well-buffered and, therefore, not likely to be acidified by atmospheric deposition of sulfur and nitrogen compounds. Most soils are also likely to be well-buffered from acidification. However, there may be areas in the monument where rock is resistant to weathering and soils and water (e.g., in potholes) may be sensitive to inputs of acidic deposition.

There is also concern that soils and vegetation in the monument may be sensitive to nutrient enrichment from nitrogen deposition. In some parts of the country, nitrogen deposition has altered soil nutrient cycling and vegetation species composition; native plants that have evolved under nitrogen-poor conditions have been replaced by invasive species better able to utilize nitrogen.

Estimates of total nitrogen and sulfur deposition can be made by adding wet and dry deposition. Wet deposition is monitored in Chiricahua NM (1999-present) as part of the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). The site ID is AZ98. Rates of atmospheric deposition of nitrogen and sulfur in rain are relatively low in Chiricahua NM, but elevated above natural conditions. The data record is insufficient for a detailed trends analysis; however, at several southwestern NADP monitoring sites (e.g., Organ Pipe Cactus NM, Guadalupe Mountains NP, Big Bend NP), both wet sulfur and wet nitrogen deposition increased from 1990-1999.

Dry deposition rates are estimated for Chiricahua NM (site CHA467), 1995-present, as part of the Clean Air Status and Trends Networks (CASTNet).

Several plant species that occur in Chiricahua NM are known to be sensitive to ozone, including Pinus ponderosa (ponderosa pine) and Rhus trilobata (skunkbush). Tropospheric (ground-level) ozone concentrations have been monitored from 1989-1992 and 1995-present. Ozone concentrations have remained somewhat steady in the monument and fall within a range that can produce visible effects or growth effects on sensitive plant species under certain conditions. However, the typical dry conditions occurring at Chiricahua NM may prevent the uptake of ozone by plants. If periods of high ozone correspond with elevated levels of soil moisture, the risk of injury may increase.

Additional information on in-park emissions at at Chiricahua NM is available in 2001 Air Emissions Inventory- Chiricahua National Monument (June 2003).

updated on 10/28/2005  I   http://www.nature.nps.gov/air/permits/aris/CHIR/index.cfm   I  Email: Webmaster