SAMI

The Southern Appalachian Mountain Initiative: A Prediction of Future Impacts of Air Pollution Control Strategies

The southern Appalachian Mountains are renowned for their beauty, wealth of natural resources, and recreational opportunities. However, these mountains are so situated that prevailing wind patterns transport air pollutants from areas of the Midwest as well as the Southeast.

In 1992, the Southern Appalachian Mountain Initiative (SAMI) was formed as a public-private regional partnership to address air quality concerns in the region. The partnership's goal is to "identify and recommend reasonable measures to remedy existing and prevent future adverse effects from human-induced air pollution on the air quality related values of the Southern Appalachians."

SAMI's region of concern is depicted in Figure 1. SAMI consists of representatives from the eight states in the region, the U.S. Environmental Protection Agency, National Park Service, U.S. Forest Service, TVA, industries, environmental organizations, and interested citizens.

SAMI is completing an integrated assessment that examines both the environmental and the socioeconomic impacts of ozone, fine particles, and acidic deposition. When completed, the final report will evaluate the need for further emissions reductions and will identify the most cost-effective approach to minimizing negative impacts from air pollution.

Approach

The assessment approach adopted by SAMI involves a comparison of several possible emissions reduction strategies:

"On the Way" (OTW) strategy assumes implementation of emissions reductions already established under the Clean Air Act (CAA) and its amendments, and under several recently promulgated regulations—State NOx Implementation Plans (SIP) and Tier II vehicular emission rules.
A more advanced strategy—"Bold with Constraints" (BWC)—would institute additional reduction measures, such as year-round (instead of summer-only) NOx controls and 90 to 95% control of sulfur emissions.
"Beyond Bold" (BB) approximates the outer limits of emissions reduction possibilities without consideration of costs.

The impacts of these three strategies were each compared one with the other and also with a baseline strategy or "No Change" scenario in which continued emission levels were limited only by long-established reduction programs under the CAA, plus Tier I vehicular emission rules. Modeling involved future projections of environmental and socioeconomic effects of acid deposition, ozone, and fine particles. Key reference years selected were1990, 2010, and 2040.

Data necessary to complete this assessment include:

Emissions inventories and models that predict future emission levels under various strategies (Figure 2). Direct costs of emissions reduction controls also are assessed.
Atmospheric chemistry and transport models that predict spatial and temporal distribution of gases and fine particles.
Environmental models that predict effects of various scenarios on forest health, stream chemistry, aquatic biology, and visibility for the reference time periods.
Socioeconomic models that focus on effects on fishing, scenery, resource stewardship, and lifestyle.

Numerous assumptions, such as projections for increases in population, vehicular miles, and electric generation, were necessary for this assessment.

Results

Emissions—Compared to 1990 levels, 2010 SO2 emissions were projected to decrease anywhere from 23% under OTW to 86% under BB. NOx emissions would decrease from 20% under OTW up to 73% with BB (Figure 2). By the year 2040, percentage decreases in SO2 were projected to be about double those in 2010 for each scenario, whereas additional decreases in NOx emissions by 2040 would be more modest. Most of the projected SO2 reductions in 2010 are attributed to the addition of scrubbers to fossil power plants.

SAMI emissions and transport modeling show that, while source states closest to a Class 1 area have the dominant impact, multiple states in the region contribute to air quality problems in each area. For example, whereas Tennessee sources have the single largest impact on air quality in the Great Smoky Mountains National Park (GSMNP), a significant portion of air pollutants come from outside the SAMI region. Thus, national strategies will be more effective than will state or limited regional strategies in addressing problems. Controls on regional utility emissions alone cannot produce the degree of benefit that is desired by some groups.

Acid Deposition—The primary components of acid deposition are sulfate and nitrogen. The OTW strategy is predicted to reduce deposition of both sulfate and nitrate-nitrogen by 50 to 60%, on average, between 1995 and 2040. The BWC and BB strategies show only 5 to 10% further deposition reductions of these two components beyond OTW.

SAMI used stream acid neutralizing capacity (ANC) as the primary indicator of stream acidity and the suitability of streams for sustaining fish and other aquatic life. Strongly acidic streams are those with an ANC less than zero. Such streams have virtually no buffering capacity and therefore have no protection from the acidity in incoming water. An early (1991-95) characterization of stream quality in the SAMI region indicated that only 2% of the streams had ANCs less than zero, with another 31% having low ANCs. Most of these low-ANC streams were located in headwater streams, especially the high elevation streams of the region.

SAMI modeling indicates that streamwater acidity across the region will change only slightly by the year 2010, regardless of the emissions control strategy adopted. However, by the year 2040, in sensitive regions that currently have strongly acidic streams, the number of such streams would increase under the "No Change" scenario. The OTW strategy is predicted to result in 30% fewer strongly acidic streams than the "No Change" scenario. BWC and BB strategies show small additional improvements over OTW.

SAMI's projections for the most sensitive ecosystems-spruce-fir and mid-elevation hardwood forests-indicate that forest health indicators generally will worsen slightly under a "No Change" scenario. Almost no difference would exist in forest health benefits of the other scenarios (OTW, BWC, and BB), even though costs would increase significantly with successively more stringent reduction strategies. All three strategies generally predict indicators of forest health to be at slightly better levels than under the "No Change" scenario.

Ozone—A cumulative growing season index was used in evaluations because SAMI is focused on impacts of ozone on forest vegetation. SAMI's ozone models indicate that a significant improvement in ozone exposure, when compared to 1993-95 baseline levels, would occur by the year 2010 with the OTW strategy. As with stream quality, strategies such as BWC and BB offer only small additional improvements. Forest response models indicate that under all scenarios, ranging from OTW to BB, little change will occur in the total growth of forests or in the mortality of trees by the years 2010 or 2040. While general forest types are not likely to change, models did predict some shifts in species composition.

Visibility—Emission impacts on visibility are most strongly influenced by sulfate and organic aerosols. Aerosol responses to the scenarios being evaluated by SAMI depend on emission changes for SO2, NOx, and VOCs. Models predict that by the year 2010, in Class 1 areas like the GSMNP, OTW would produce rather small improvements in visibility while the BWC and BB strategies would produce progressively greater improvements (Figure 3). By 2040, all three strategies would produce improvements, with each more aggressive strategy again noticeably better than its counterpart. All improvements would be greatest on days when visibility is the poorest, which means that the greatest improvements are predicted to be during the summer months. The greatest improvements are predicted for the Class 1 areas nearest the center of the SAMI region, such as the GSMNP and the Shenandoah National Park.

Socioeconomic—While all strategies appear to result in conditions that are substantially better than a continuation of the current baseline emission levels, no dramatic differences are noted in most effects between the various other strategies (OTW, BWC, and BB). SAMI's assessment predicts that no dramatic change will occur from current patterns of the three strategies with respect to fishing, visibility, or lifestyle.

Summary

The SAMI experience has taken a great deal of effort and time, but it has resulted in the first regional air quality assessment that has considered multiple emissions (sulfur and nitrogen) and multiple impacts (acid deposition, visibility, and ozone). Many new methods had to be developed to complete the assessment, but SAMI's work is technically sound. While the models used may not be perfect, the regional stakeholders are better informed because of these analyses. And SAMI has developed some good tools that can be used in the future. Furthermore, SAMI's results appear to validate current emission control plans designated in the "On the Way" strategy, and the results indicate that emissions reductions from all sources and regions will be required to significantly improve mountain air quality. How SAMI's analyses will be used remains to be determined.

Information Contacts

Stephen F. Mueller, (256) 386-3643, sfmueller@tva.gov

Last updated on 8-9-2002.
Inquiries and comments should be sent to wjparkhurst@tva.gov.