On the Air

Below are summaries of technical reports on important air quality issues. Click on the links at left to go directly to the reports.

Nitrogen Deposition Effects on the Terrestrial Environment

Science – As total nitrogen emissions of human origin rose in recent decades, interest increased in the potential for impacts on the environment. Symptoms of nitrogen saturation have been identified in several localized regions and certain ecosystems of the United States. The possible impacts of increases in total nitrogen deposition on the terrestrial environment include decreases in soil and plant tissue nutrient levels and reductions in species biodiversity.

Policy – Currently, nitrogen emissions are regulated under Titles I (National Ambient Air Quality Standards and State Implementation Plans), II (motor vehicles) and IV (acid rain) of the Clean Air Act. In the 1980's and 1990's, the majority of research to address "acid rain" primarily focused on the effects of sulfur dioxide deposition rather than nitrogen deposition, though nitrogen emissions reductions were included in acid rain regulations. Currently, nitrogen emission regulations call for large reductions in utility nitrogen emissions as well as some reduction in vehicle nitrogen emissions; however, agricultural sources of nitrogen (e.g., ammonia) are not currently regulated.

Three Decades of Mercury Levels in the Tennessee River System

Science – Mercury is a metallic element. Once mercury enters the atmosphere it continuously circles the globe until it is converted to a form that can be deposited to the earth's surfaces. Atmospheric mercury originates from many natural and human-caused sources around the globe. A cycle forms as deposited mercury is re-emitted into the atmosphere by evaporation from soil, water, and other surfaces. The mercury in this worldwide environmental cycle is termed the global pool. New mercury emissions enter the mercury cycle and contribute to total atmospheric mercury. As part of its stewardship responsibilities, the Tennessee Valley Authority collects sediment and fish tissue samples for mercury analysis across the Tennessee Valley watershed. Mercury levels in sediment in the Tennessee River system have substantially declined over the last three decades. "Hot spots" appear to be the result of historical industrial activity, particularly by past mercury-intensive processes used in the chlor-alkali industry.

Policy – The United States Environmental Protection Agency has focused its concerns about mercury on levels in fish because fish consumption is the primary human exposure pathway. However, there is currently great uncertainty about the benefits of attempts to implement costly regulations on mercury emissions from fossil fuel power plants in the U.S. Recent modeling studies have indicated that U.S. utilities account for only about 1 percent of new global emissions caused by human activity.

Fine Particle Levels in the Great Smokies

Science – Understanding sources of aerosols requires a complex analysis of data obtained by continuous monitoring of a "background" site. After sulfates, carbon-containing constituents comprise the largest fraction of fine particle mass in the southeastern U.S. The Tennessee Valley Authority’s research at Look Rock, on the western edge of the Great Smoky Mountains National Park, continues to make progress in its investigation of the sources of carbon-based particles. The research serves as a basis for suggesting appropriate environmental management strategies.

Policy – Knowledge of all the sources of fine particles is essential to the development of approaches that are effective in the achievement of the health-based fine particle National Ambient Air Quality Standard and in the improvement of visibility in Class I areas. Background monitoring helps evaluate whether control strategies are effective in meeting regulatory goals.

The ARIES Study

Science – Results from the ongoing Aerosol Research and Inhalation Epidemiology Study (ARIES)—a comprehensive study on the effects of air pollution on human health—indicate that carbon monoxide gas and fine particles that contain carbon are the most hazardous components of air pollution. These results dispute previous assumptions that all types of fine particles (PM2.5) are equally toxic.

Policy – Data from ARIES suggest that the focus of fine particulate standards and emissions management strategies should be altered. Instead of including all types of fine particles, using the overly broad total PM2.5 mass, the focus should be on the components that may be the primary causes of adverse human health effects.

Dust in the Wind: The Challenge of Fine Particles

Science - TVA has been monitoring fine particulates (PM2.5) since 1978, but a comprehensive, Valley-wide network did not begin operation until 1999. While measures of larger particle size air pollution indicate significant improvements over the last two decades, PM2.5 measurements have not been collected long enough to establish meaningful trends. Monitoring results confirm that many urban areas and some rural areas in the eastern U.S. will have a tough time meeting the stringent annual fine particle standard. Many areas may drift into and out of attainment.

Policy - In September 1997, the EPA adopted a stringent revision to the particulate matter (PM) clean air standard. This new standard assumes that all fine particles, regardless of their makeup, have the same impacts on human health. These standards have important environmental, economic, and regulatory implications for the Tennessee Valley and the nation.

Whatever Happened to Acid Rain?

Science - The effects of acid deposition have been a concern in the U.S. and elsewhere for over three decades. In response, eastern North American power plants have achieved major reductions in sulfur dioxide emissions, one of the acid rain precursors. Reductions in deposition of total acidity have also been achieved over the past 20+ years, but to a smaller extent due to the increasing nitrogen contributions from vehicle NOx emissions and agricultural NH3 emissions. Major recoveries of sensitive ecosystems, especially high elevation forests, have yet to be seen. Models indicate that prevention of further deterioration is the most realistic goal over the next few decades.

Policy - Concerns about “acid rain” drove research in the 1980’s on air quality impacts and led to the 1990 Clean Air Act Amendments. Today, health effects of ozone and fine particulate matter and visibility effects have supplanted acid deposition as air quality issues of highest attention. Reductions in sulfur dioxide and nitrogen oxide emissions designed to reduce ozone and particulate matter and improve visibility will simultaneously help prevent deterioration of ecosystems sensitive to acid deposition.

How Clean is The Air?

Science - Contrary to popular perception, air quality in the TVA region, with few exceptions, is substantially better today than it was when the first national clean air standards were adopted in 1971.

Policy - The air quality issues and management solutions of today are larger, more complex and more challenging than ever before. Many issues associated with primary pollutant emissions–such as suspended particles, sulfur dioxide and carbon monoxide–have been resolved. But, the tougher secondary pollutants (such as ozone and fine particles) and values related to air quality (such as visibility impairment, global climate change and acidic deposition) remain controversial and a challenge.

The Role of Renewable Energy in Reducing Greenhouse Gas Buildup

Science - Unlike electricity produced from the combustion of fossil fuels, electricity produced from solar, wind, landfill gas, biomass, and increasing existing hydroelectric capacity does not contribute to the buildup of greenhouse gases (GHG) in the atmosphere. Such renewable energy sources appear to be one way that utilities can address the buildup of GHG, thus reducing the potential impact on climate change. In the Tennessee Valley, the modernization of hydroelectric facilities is the least expensive method among those listed per unit of power generated. Co-firing wood waste with fossil fuel is second. But when emphasis is placed on reducing GHG emissions alone, landfill gas and co-firing wood waste are the most cost-effective methods.

Policy - One approach to addressing the Administration’s Global Climate Change Initiative may include increasing the use of renewable energy sources in electric power production. TVA is evaluating renewable energy sources, along with other types of GHG mitigation technologies and options, to determine the costs and problems associated with integrating them into the system and the timing of implementation.

Outdoor Ozone Monitors Over-Estimate Actual Human Ozone Exposure

Science - Continuous outdoor monitoring of ozone levels is useful for many purposes, but indoor air monitoring and personal measurements are the best ways to estimate actual day-to-day human ozone exposure. The study described here indicates that actual personal exposures are only 7 to 31% of the ozone levels measured by conventional outdoor monitors. During ozone season, the amount of time spent outdoors and time spent with windows open are major determinants to personal exposure.

Policy - Much effort is expended by the U.S. EPA and state and local regulatory programs to inform the public when outdoor ozone levels are unacceptably high. However, indoor air monitoring and personal ozone exposure measurements suggest that most of us are not exposed to unhealthy doses of ozone. From a public health perspective, when ozone levels are in the unhealthy range (Orange Air Quality Index or higher), most people—especially sensitive individuals—should limit prolonged outdoor exertion and reduce their ozone exposure by staying indoors.

Modeling Air Quality-Recent Advances and Challenges

Science - Due to advances in air quality modeling, we can now evaluate the regional impact of various emission control scenarios on many pollutants simultaneously. These complex models combine meteorological and emissions data to project atmospheric chemical reactions for an array of pollutants across large regions.

Policy - Decisions about air quality regulations and emissions control strategies have been heavily influenced for years by the predictions of atmospheric models. The accuracy of these complex models and the manner in which they are applied is becoming increasingly important, as regulatory agencies and interest groups become ever more reliant upon their outputs.

The Challenge of Improving Visibility

Science - Declines in visible range measurements in America’s scenic areas are attributed to increased airborne concentrations of fine particles that scatter light and produce a hazy view. Particles emitted by combustion sources are often at or below the critical size range for light scattering. But high relative humidity can enlarge some of the ultra fine particles – linking emissions and weather to visibility impairment. Models that can predict the impact of various power plant emissions scenarios on visibility are being tested and revised. A major challenge is to improve our understanding of what controls a critical component — particle size distributions.

Policy - TVA is a participant in a regional collaborative effort called VISTAS, established by state and tribal governments and federal agencies to plan and coordinate activities with the U.S. EPA to develop plans for achieving “natural” levels of visibility across the U.S. within 60 years. One of VISTAS’ first tasks will be to evaluate an air quality model for predicting the impact of different emission control strategies on visibility.

Sulfur in the Southern Appalachians

Science - Airborne sulfur dioxide emissions contribute to fine particle air pollution, visibility impairment, and acid rain. However, both weather and chemistry combine to obscure the relationship of sulfur dioxide emissions to these problems. Environmental trends often are difficult to establish.

Policy - In meeting national clean air standards and acid rain control requirements, TVA has reduced its system-wide sulfur dioxide emissions by more than two-thirds over the past decade. While most regional sulfur-related pollution has declined, particle sulfate concentrations in the air have improved little, if any.

Ozone Impacts on Forests

Science - Recommendations to date for the U.S. Environmental Protection Agency (EPA) secondary ozone standard have been based largely on short-term chamber studies of annual crops and a few tree species. Such studies have proven to be poor predictors of forest-level impacts.

Policy - Results of the Regional Ozone Vegetation Effects (ROVE) studies indicate that caution must be used when basing regulatory conclusions regarding environmental effects of ozone on forests solely on short-term seedling chamber studies.

Cumberland Steam Plant Sulfur Emissions

Science - Comparisons of plumes from Cumberland Steam Plant before and after installation of Flue Gas Desulfurization indicate that the lower sulfur dioxide emissions have led to reductions in particle sulfate and a corresponding improvement in visibility within the plume.

Policy - TVA’s system-wide sulfur dioxide (SO2) emissions declined 48 percent between 1975 and 1990, and these emissions are projected to decline an additional 55 percent between 1990 and 2010. Although many questions remain unanswered, results from this study indicate that reductions in TVA’s SO2 emissions, while perhaps obscured by other sources of regional SO2, should result in comparable improvements in regional visibility because of reduced formation of sulfate aerosols.

Chemical Composition of Fine Particles in Tennessee Valley Air—and Why It Matters

Science - PM2.5 measurements indicate that the Tennessee Valley will have difficulty meeting more stringent annual National Ambient Air Quality Standards. And additional information on the chemical composition of fine particles is needed before deciding how to most effectively lower PM2.5 mass levels. Preliminary data suggest that summer reductions either in the precursors to organic particulate matter or in SO2 would be equally effective in achieving reduced PM2.5 mass levels in the Tennessee Valley.

Policy - Reducing fine particle levels will be a difficult and costly task. If the mass-based PM2.5 standards are retained, development of cost-effective, efficient control strategies likely will justify calls for emission reductions of precursors of both organic particulate matter (chiefly vehicular and wood-burning emissions) and sulfates (chiefly power plants) from all sources in the Valley. Strategies should not be focused on large point sources of SO2 alone.

Power Plant Mercury Emissions and Human Health: What are the Central Issues?

Science - Health concerns regarding mercury, for the most part, focus on the potential for developmental damage to infants caused by high mercury levels in fish consumed by mothers during pregnancy. Mercury is a global problem. Much of the mercury in the environment today comes from outside the United States, and from the re-circulation of past emissions from both natural and human-made sources.

Policy - In efforts to reduce emissions of mercury, the U.S. EPA has pointed to U.S. power plants as the major source of "new" mercury emissions. Preliminary data indicate that coal-fired power plants account for about one-third of "new," human-made mercury air emissions in the United States. Globally, however, U.S. power plants account for approximately 1 percent of all current mercury emissions.

Some Years Up, Others Down, but Ozone Concerns are Here to Stay

Science - In the Southeastern United States, both natural and human-made factors conspire to make ozone a difficult-to-solve environmental problem. Although ozone exposures vary considerably in time and space, rural ozone patterns show no overall trend from 1988 through 2000.

Policy - No matter which standard or index is considered, rural ozone levels in the Southeast may be a concern. The newer 8-hour standard is substantially more stringent than the older 1-hour standard. For most rural areas, exceeding the level of the 1-hour standard is a rare occurrence, whereas exceeding the level of the 8-hour standard occurs frequently.

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

Science - Results from the Southern Appalachian Mountain Initiative (SAMI) indicate that emissions reductions under the existing Clean Air Act alone would still result in some deterioration of streams, forests, and visibility in sensitive areas of the southern Appalachian region over the next 8 to 40 years. Recent regulations requiring emissions reductions from both power plants and vehicles will prevent further deterioration by reducing emissions and ozone levels. SAMI modeling also indicates that stricter emission regulations beyond those recently promulgated would not result in much further improvement, except in the area of visibility.

Policy - SAMI analyses indicate that, except for visibility, regional emissions reduction requirements beyond those already established will produce little environmental benefit. However, a national emissions control strategy likely would benefit air quality in the southern Appalachians more than a narrow regional approach. However, vehicular and other emission sources need to be targeted, not just power plants.

Indoor Air Quality: A Serious Health Issue

Science - As people spend growing amounts of time indoors, and as buildings become more airtight to improve energy efficiency, exposure to indoor air pollution has become an increasingly serious health problem. Radon, tobacco smoke, combustion products, and a wide variety of particles and vapors head the list of pollutant sources posing risks to human health.

Policy - Public awareness of the numerous sources of indoor air pollution and of methods of reducing exposure to these pollutants is essential to reducing one of the top five environmental risks to public health in America.

TVA's Air Quality Monitoring Networks Promote a Cleaner and Greener Nation and Region

Science - TVA has made many contributions to promote a better understanding of air quality. And while TVA cannot claim to have written the proverbial "book" on air quality monitoring, the Agency certainly can take credit for contributing to many chapters. TVA's national air monitoring "firsts" include operating the first automated air quality monitoring network, the first U.S. acid rain monitoring study, and the first eastern U.S. visibility monitoring station.

Policy - TVA began air quality monitoring and research programs in the early 1950s. The data from these monitors have been used to measure TVA compliance with national clean air standards, support the operation of TVA power generation facilities, give proper focus to environmental management initiatives, address emerging air quality issues, and assist in promoting economic development in the region. TVA currently supports 23 air quality monitoring stations across 5 networks in the Tennessee Valley.

Management of Greenhouse Gases Through Carbon Sequestration: TVA/DOE/EPRI Collaborative Projects

Science - The level of carbon dioxide in the earth's atmosphere continues to increase to a degree that has been predicted to affect the global climate. TVA is working on three DOE-funded research projects to develop and evaluate new technologies for removing and storing atmospheric carbon dioxide.

Policy - To address worldwide concerns that greenhouse gas increases may cause significant changes in global climate systems, the Bush Administration announced a voluntary 10-year Global Climate Change Initiative for the United States. The objective is to develop innovative technologies to reduce net emissions of such gases. TVA is partnering with the U.S. Department of Energy and EPRI in efforts to help develop such technologies.

Ozone Forecasting Provides Valley an Early Warning System for Unhealthy Air Quality

Science - Beginning on May 1, 2001, TVA and its Valley environmental regulatory partners began forecasting next-day ozone levels to help notify Valley residents when ozone might reach unhealthy levels. This effort combines today's ozone measurements with tomorrow's weather forecasts to help estimate tomorrow's maximum 8-hour ozone concentrations. These forecasts are used to inform the public and initiate voluntary ozone management activities.

Policy - In keeping with TVA's environmental stewardship role, this effort promotes understanding and awareness of air quality issues. TVA provides next-day summertime ozone forecasts to environmental regulatory organizations for the metropolitan areas of Memphis, Nashville, Chattanooga, KNOxville, Bristol-Kingsport, and the high-elevations of the Great Smoky Mountains National Park.

Sources of Organic Fine Particles Using Carbon-14 Measurements

Science - Scientists know that about 30 percent of the fine-particle mass (PM2.5) in ambient aerosols is organic particles. Methods for pinpointing the sources of these particles are difficult and expensive. Measuring the carbon-14 content of organics allows one to separate "modern" sources from "fossil" sources rather easily. This method enables us to distinguish fossil-fuel-burning sources of carbon (largely vehicles) from plant-derived sources (usually vegetation emissions and wood-burning).

Policy - Understanding the sources of the significant organic component of PM2.5 is critical to determining what portion of this organic fraction of fine particles may be controlled, as well as how, and at what times of the year this control may be achieved.