Performance Measures

Air Quality Conditions and Trends

The National Park Service (NPS) measures the success of its air resource management program based on results achieved. Monitoring data show that air pollution is affecting some park resources - like visibility - nationwide. Therefore, consistent with the Government Performance and Results Act, the NPS has established three air quality goals to meet by September 30, 2012:

• visibility in 95% of NPS reporting parks has remained stable or improved;
• ozone in 89% of NPS reporting parks has remained stable or improved; and
• atmospheric deposition in 79% of NPS reporting parks has remained stable or improved.

The NPS Air Resources Division oversees the air resource management program. We think it is important to measure the program's effectiveness based on outcomes even though the NPS has no authority to regulate sources of air pollution located outside park boundaries. We believe we can make a difference by: (1) acquiring high quality data, (2) making that information available to the general public, and (3) identifying and seizing opportunities to participate in decisions being made by regulatory agencies that might affect air quality in parks.

We use several indicators to measure progress. One indicator looks at visibility trends on the clearest and haziest days. Another tracks changes in ozone concentrations based on the 3-year average of the annual fourth highest daily maximum 8-hour concentration. The final indicator focuses on wet deposition of sulfate, nitrate, and ammonium ions. An area meets each of the above goals if it does not show statistically significant deterioration in any of the performance indicators used for individual goals during the most recent 10-year period for which data is available.

Beginning with the 1996-2005 analysis, the NPS expanded its reporting to include not only parks with on-site air quality monitoring, but also parks with nearby monitoring. This increased the number of reporting parks from 52 to 141. For the latest analysis, which covers the years 1998-2007, we were able to report on a total of 147 parks for one or more of the three air quality indicators. Of these, 99 percent of the reporting parks showed stable or improving trends in visibility, 94 percent showed stable or improving trends in ozone concentrations, and 83 percent showed stable or improving trends in atmospheric deposition.

In addition to determining the trends in air quality, the NPS is interested in determining the current condition of the air resources within NPS units. A stable trend in air quality may not be sufficient to protect an area that is already experiencing poor air quality. For this reason we have developed an index for assessing current air quality conditions at parks throughout the country that assigns parks to one of three categories:

• Condition Red–a Significant Concern,
• Condition Yellow–in Moderate Condition, or
• Condition Blue–in Good Condition.

The procedures for estimating the air quality parameters and assigning condition categories are described in the Air Quality in National Parks 2008 Annual Performance & Progress Report (pdf, 4.8mb). Air quality conditions and trends are depicted graphically as maps and data plots in the report.