The quality of the air that we breathe is generally healthful and good. That hasn’t always been true, however. During the decade of the ’60s, prior to air pollution laws, the air in Tennessee’s cities was often thick with smoke and soot from uncontrolled air emissions from factories, the growing number of automobiles and the prevalent use of coal for fuel in industry and in our homes.

Over the past 25 years, Tennesseans have seen remarkable progress in cleaning up our air. Although the earliest improvements in visibility have been the most obvious, air quality data collected across the state since the early 1970s show a steady trend toward improved air quality for all the major pollutants.

Air pollution occurs when airborne contaminants are present in ambient (outdoor) air in levels that are high enough and continue long enough to harm human health, property or welfare. Natural sources of airborne contaminants, such as forest fires and bi ological processes, are often significant sources of emissions; however, human activities usually make the greatest contributions to emissions in urban and industrialized areas.

Ozone is formed through a series of complex reactions involving chemical compounds in the atmosphere during periods of intense sunlight. Ozone levels are lowerst during the night and early morning hours. However, as the sun rises, ozone levels begin to climb. These maps show hypothetically how ozone and chemical emissions that contribute to ozone formation can be transported from one area to another and how ozone forms and accumulated during the day. The combination of intense sunlight, warm temperatures, stagnant high-pressure weather systemsand low wind speeds can cause ozone to form and acculumate around mid-day as chemical emissions build up in the atmosphere. Ozone levels tend to peak around mid-afternoon, when temperatures are highest. Scientists are studying ozone formation to determine how it can be controlled.

Both natural and human-made pollutants may harm human health and welfare. Air pollutants can aggravate or cause respiratory illnesses, injure vegetation, decrease crop yields, rust metals, discolor house paint and reduce visibility. Most damage is caus ed by exposure to one of six pollutants at high levels over a period of time — particulate matter, ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide and lead. Because they are the most widespread and most dangerous to human health, the U.S. Enviro nmental Protection Agency (EPA) has classified these air contaminants as “criteria pollutants.”

In addition to the adverse effects that high ambient concentrations of the criteria pollutants might have on health and welfare, failure to attain ambient air quality standards under the regulations jeopardizes industrial growth and economic expansion.

Within nonattainment areas, proposed major industrial developments or expansions can be accomplished only if new emissions of pollutants contributing to the nonattainment are offset by reductions from existing sources. This discourages major industrial developments and expansions in nonattainment areas.

Tennessee has made excellent progress in controlling the criteria pollutants. New provisions in the 1990 Clean Air Act Amendments are aimed at further reducing motor vehicle, power plant and industrial source emissions to protect and improve our nation’ s air quality.

Hazardous Air Pollutants

In the early 1970s, the EPA began setting national standards to control emissions of air pollutants considered to be hazardous. National air quality standards were issued for asbestos, benzene, beryllium, inorganic arsenic, mercury, radionuclides and vin yl chloride. Although existing standards for the criteria pollutants and volatile organic compounds (VOCs) have reduced emissions of many hazardous air pollutants, the EPA is developing new standards which will regulate emissions of 189 hazardous air pollutants by th e year 2000. These regulations will address specific emissions from particular types of operations, such as the printing industry and drycleaning operations.

Today’s Challenges

According to the EPA, ground-level ozone and particulate matter are two of the most serious air pollution problems facing the nation today.

High above the earth’s surface, ozone in the stratosphere works as a filter of the sun’s harmful ultraviolet rays; however, ground-level ozone, a major component of smog, can be harmful to human health and vegetation. At high concentrations, ozone can cause respiratory irritation and aggravate lung disease in some individuals.

Considered to be one of the most widespread air pollution problems in the South, ground-level ozone results from a series of reactions between atmospheric nitrogen oxides and VOCs, or hydrocarbons, in the presence of sunlight. Emissions from vehicles, power plants, industries, airplanes, lawn mowers and other internal combustion processes usually contribute the greatest amounts of these chemical compounds; however, scientific studies now show that a large percentage of the VOCs that contribute to ozone formation in the Southeast are produced by natural sources.

The Southern Oxidants Study - a strategic alliance of research scientists, engineers and air quality managers from universities, federal and state governments, industry and public interest groups - has reported that the natural emission of VOCs from vegetation, particularly trees, is the dominant source in the rural South and in many Southern cities.

By the time the 1990 Clean Air Act Amendments were passed, only three areas of the state did not meet the ozone standard and were designated by the EPA as "nonattainment." Two of these areas, Knox County in East Tennessee and Shelby County in West Tennessee, have now been reclassified as attainment.

To help address the Middle Tennessee ozone nonattainment problem, in December 1994, vehicle emissions testing was expanded from Nashville-Davidson County alone to the five-county ozone nonattainment area. This area includes Davidson, Rutherford, Sumner, Williamson and Wilson counties. Because the ozone standard is now being met, the EPA is considering redesignating this area to attainment. Any area not meeting the ozone standard by 1996, however, will be subject to greater emission restrictions on area businesses and industries.

Particulate matter includes solid particles and liquid droplets in the air, such as dirt, dust, smoke and soot. Prior to 1980, states were required to measure the combined total of small and large particles in the air as total suspended particulate (TSP). Because larger particles are usually filtered out in the nose and throat, they are not especially hazardous to human health; however, smaller particles can be easily inhaled and become trapped in the lungs. The emphasis has now shifted to measuring only those small particles.

Historical data show that 12 relatively small areas of Tennessee exceeded the ambient standard for TSP prior to 1980. Monitoring data for smaller particles show that Tennessee is now maintaining the standard; no areas of the state are classified as nonattainment for this criteria pollutant.

Two areas in Tennessee previously designated as sulfur dioxide nonattainment areas are being considered for reclassification to attainment status - an area consisting of small parts of Benton and Humphreys counties and an area in southern Polk County. No violations of the ambient standard have been recorded in these areas in nearly a decade.

In 1980, the national ambient air quality standard for carbon monoxide- was not being achieved in small urban areas of three of Tennessee’s largest counties — Knox, Davidson and Shelby. Since that time, strict federal emission standards for new ve hicles have significantly decreased carbon monoxide emissions. Today, all of Tennessee is in compliance with the national standard for carbon monoxide.

Source: U.S. Environmental Protection Agency, Pollutant Standards Index data reported by Chattanaooga, Knoxville, Memphis and Nashville

Twenty years ago, lead from gasoline-powered internal combustion engines, primarily motor vehicles, was a widespread problem. Since lead compounds are no longer used in gasoline, nonattainment of the ambient air quality standard for lead is suspec ted only near industrial operations that process lead-containing materials or use them in manufacturing operations. Today, the primary source of lead exposure in Tennessee is not from ambient air, but from the existence of lead-based paints used in house holds prior to 1978.

During the 1980s, three small areas in Tennessee were designated as nonattainment. These areas, located in Fayette, Shelby and Williamson counties, each contained one industrial operation that caused exceedances of the ambient standard. The Fayette Coun ty source ceased operation in 1992, and this area has been redesignated as attainment.

Air quality data collected in the Shelby and Williamson county areas indicate the ambient standard has not yet been achieved continuously. Plans have been submitted for reducing lead emissions to ensure that these areas soon achieve and maintain the stan dard.

There have been no exceedances of the air quality standards for nitrogen dioxide in Tennessee.

How do we know when the air we breathe is unhealthy?

If you live in Davidson, Hamilton, Knox or Shelby counties, you can probably get this information from your local weather forecast. Local air pollution programs in these counties report air quality data, or pollution index data, to local news media.

This information is used to advise the public about general health effects associated with different pollution levels and to describe any precautionary steps citizens may need to take.

The Pollutant Standards Index (PSI) was developed by the EPA to provide a uniform, nationwide method of describing air quality and includes information on emissions of carbon monoxide, ozone, nitrogen dioxide, sulfur dioxide and particulate matter. This index classifies air quality concentrations as good, moderate, unhealthful, very unhealthful or hazardous, based on a scale of 0 to 500. A PSI of less than 100 indicates that air quality is within ambient standards. However, a PSI in excess of 100 may j ustify a health advisory for persons who are sensitive to air pollutants to limit outdoor activities for that day.

PSI data reported by Tennessee’s four major cities since 1980 demonstrate a steady improvement in air quality.

Cumberland Power Plant Reduces Emissions

Courtesy Tennesee Valley Authority

One of 11 Tennessee Valley Authority fossil plants operating throughout the TVA system, the Cumberland Fossil Plant generates up to 2,600 megawatts of power. The plant’s two operating units together burn about 1,000 tons of coal per hour, or about 6 million to 7 million tons annually.