National Park Service


Date of this Version



Natural Resource Report NPS/NGPN/NRR 2016/1178 / NPS 920/132137, March 2016, viii, 52 pages

Published by the United States Department of the Interior, National Park Service, Natural Resource Stewardship and Science, Fort Collins, Colorado

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Please cite this publication as:

Sullivan, T. J. 2016. Air quality related values (AQRVs) for Northern Great Plains Network (NGPN) parks: Effects from ozone; visibility reducing particles; and atmospheric deposition of acids, nutrients and toxics. Natural Resource Report NPS/NGPN/NRR—2016/1178. National Park Service, Fort Collins, Colorado.


United States government work. Public domain material.



This report describes the Air Quality Related Values (AQRVs) of the Northern Great Plains Network (NGPN). AQRVs are those resources sensitive to air quality and include streams, lakes, soils, vegetation, fish and wildlife, and visibility. This report also describes air pollutant emissions and air quality in NGPN, and their effects on AQRVs. The primary pollutants likely to affect AQRVs include nitrogen (N) and sulfur (S) compounds (nitrate [NO3-], ammonium [NH4+], and sulfate [SO42-]); ground-level ozone (O3); haze-causing particles; and airborne toxics.

The 13 parks that are included in the NPS Inventory and Monitoring (I&M) Program, and discussed in this report, are Agate Fossil Beds National Monument (AGFO), Badlands National Park (BADL), Devils Tower National Monument (DETO), Fort Laramie National Historic Site (FOLA), Fort Union Trading Post National Historic Site (FOUS), Jewel Cave National Monument (JECA), Knife River Indian Villages National Historic Site (KNRI), Missouri National Recreational River (MNRR), Mount Rushmore National Memorial (MORU), Niobrara National Scenic River (NIOB), Scotts Bluff National Monument (SCBL), Theodore Roosevelt National Park (THRO), and Wind Cave National Park (WICA). Three of the parks (THRO, BADL, and WICA) are Class I areas, giving them a heightened level of protection against harm caused by poor air quality under the Clean Air Act (CAA).

In general, air quality in the NGPN is considerably better than in most other areas of the United States. Nevertheless, there have been several large coal-burning power plants in North Dakota, Nebraska, and eastern Montana, and emissions from those facilities may impact NGPN parks to some degree. Several of the power plants are located very close to KNRI. Other network parks are more distant from large emissions sources. The parks are relatively remote from cities and associated air pollution sources, and there are few urban centers of any magnitude near this network, although Denver is close to the southwestern network boundary. Recent and future increases in oil and gas (O&G) development in eastern Montana, western North Dakota, and surrounding states may increase air pollution in the network area by an unknown, but potentially substantial, amount.

County-level sulfur dioxide (SO2) emissions in 2012 were low in the NGPN region, except in the area along the Missouri River near KNRI, where several power plants emitted collectively around 80,000 tons per year (tpy) of SO2. Emissions were similar in magnitude in 2002, the emissions year used for two NPS risk assessments (Sullivan et al. 2011a, Sullivan et al. 2011b) referred to in this report. Annual county-level N emissions were higher than SO2 emissions, and in the area near KNRI, power plant N oxides (NOx) emissions were around 46,000 tpy in 2012. These emissions levels were lower than the 72,000 tpy of NOx reported in 2002, due to more recent combustion controls. Power plant emissions of S and N are expected to further decrease in the future because of requirements of the Regional Haze Rule (RHR), intended to reduce haze and improve visibility in Class I areas.

Near THRO, hundreds of small oil wells adjacent to the park emit both N and S. While the emissions per well may not be large, the combined emissions of N from all the wells may be substantial. Some wells are very close to park boundaries where there could be acute or chronic impacts to vegetation and visibility on a local basis. The cumulative effects of the numerous small N sources collectively constitute an important resource concern at THRO and elsewhere in NGPN, but emissions from these small, but very numerous, sources are not well quantified. Agricultural activities are also a source of N emissions, in the form of ammonia. Agricultural emissions in and near NGPN are also not well quantified.

Sulfur and N pollutants can cause acidification of streams, lakes, and soils. Surface waters in NGPN are likely well buffered against acidic inputs because they generally contain sufficient amounts of base cations, like calcium (Ca2+) and magnesium (Mg2+), that buffer deposition acidity. At this time, neither aquatic nor terrestrial effects from acidic deposition are expected to be important in this network.

Nitrogen pollutants can cause undesirable nutrient enrichment of natural ecosystems, leading to changes in plant species diversity. Nitrogen deposition is relatively high in the southeastern portions of the network region, and vegetation in several of the parks may be at risk. Grasslands are known to be sensitive to N enrichment. Much of the northern Great Plains is covered by mixed-grass prairie or shortgrass prairie, with tallgrass species generally more common on microsites with higher soil moisture. The mixed-grass prairie of BADL is a good example of the highly valued prairie ecosystems that have largely been extirpated from their former range. Grasslands of the Great Plains have experienced invasions of non-native grasses and woody plant species that appear to be driven, at least in part, by N enrichment of soil and fire exclusion (Köchy and Wilson 2001, Tilman et al. 1997). In addition, recent studies suggest that low productivity, sparse badland shrublands may be even more sensitive than grasslands to N enrichment.

Ozone pollution can reduce plant growth and cause visible injury to foliage. Several O3-sensitive plant species, including ponderosa pine (Pinus ponderosa), are present in most parks in this network. Ozone exposure indices, including the W126 and SUM06, are low in most network parks, SCBL being the exception. Generally low soil moisture levels during the O3 season (summer) likely preclude O3 injury to plants, but plants have not been examined for O3 injury in NGPN. Ozone exposure may become a more important concern in the future in response to local and regional NOx emissions from continued O&G development.

Particulate pollution can cause haze, reducing visibility. Visibility is a key AQRV in this network, and a source of concern because of the magnificent vistas in and around the NGPN parks. Some parks in the network have experienced moderately impaired visibility. The majority of haze in all three monitored parks is attributable to SO42- derived from SO2 emissions, NO3- from NOx emissions, coarse mass (e.g. soil), and organics. Increased O&G activities in the region are likely to increase haze levels in the future.