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Air Quality Issues of Electricity Production:
Ozone (Smog) and Fine Particulates

While Climate Change and Acid Rain impact the general environment on a regional or global scale, air emissions from fossil fuel power plants also have direct impacts on human health. Most especially, human health is jeopardized from the formation of ozone (or "smog") and fine particles that result from fossil fuel combustion technologies. Ozone is formed as a result of chemical reactions of nitrogen oxides emitted into the atmosphere; fine particulates may form either in power plant smokestacks or in the air as a result of the emissions of any of the three primary gasses from fossil generation plants - carbon dioxide, sulfur dioxide or nitrogen oxides. Both ozone and fine particulates pose health risks within the vicinity of the emitting power plants or may travel hundreds of miles and pose health risks far from the sources of the precursor emissions.


What is ozone?

Ozone is a molecule comprised of three oxygen atoms linked together. Stratospheric ozone provides a vital protective shield against the sun's ultraviolet radiation and occurs naturally in the upper reaches of the atmosphere. Tropospheric ozone, in contrast, can be extremely harmful to human health and the environment as it becomes a major pollutant when created at ground level.

Ozone is not emitted directly into the environment. It is produced by a complex chemical reaction when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. NOx is produced when cars and trucks, electric power plants and industrial processes burn fossil fuels. VOC's are unstable and easily-evaporated organic compounds present in vehicle exhaust, paint fumes, and industrial process waste. The interaction between these two chemicals create ozone pollution, the primary harmful ingredient in urban smog.

Weather conditions are critical to ozone formation, which is greatest during the summer, when long hours of sunlight and high temperatures speed the photochemical reactions that produce ozone. These chemical reactions take place while the pollutants are being blown through the air by wind. What this means is that ozone pollution can be far more severe many miles away from the original power plant site that generates the NOx precursors. As a result, tall smokestacks that emit NOx can contribute to air pollution build-up in downwind states located hundreds of miles away.

What are the consequences of ground level ozone?

At ground level, ozone can damage humans, green plants and everyday materials.

Human Health Effects
Ozone reacts readily with membranes lining the lung's air passages as well as the eye. Mounting scientific evidence links ozone to a number of short- and long-term respiratory and visual problems:

  • Decreased ability of the lungs to function properly, increasing respiratory illness, especially in children that are active outdoors.
  • A long list of breathing problems: shortness of breath, coughing, wheezing, chest tightness, headaches and nausea.
  • Pronounced allergic reactions.
  • Increased hospital admissions for respiratory problems, especially for children with pre-existing conditions such as asthma.
  • Reduced ability to exercise resulting in poor athletic performance.

Plants and Crops
Ozone interferes with the ability of green plants to convert sunlight into useful energy. This interference with the normal photosynthesis process causes damage to agricultural crops, commercial timber and natural forest ecosystems, ornamental plants (grass, flowers, shrubs, trees) and other natural flora. The EPA estimates that ground-level ozone pollution is responsible for several hundred million dollars in annual losses from reduced crop yields.

Ozone damages rubber products, dyes and paints, fabrics, plastics and electrical components. The damage comes in the form of corrosion, fading and cracking.

How does electricity production contribute to ozone formation?

Electric power plant emissions account for about one-third of all NOx released into the atmosphere from human sources. As noted, NOx is the major precursor of ground-level ozone.

NOx emissions rates can vary significantly among generating companies, individual power plants and geographic regions. A 1997 study conducted by the Natural Resources Defense Council, Public Service Electric and Gas and the Pace Energy Project found that the emissions per unit output of electricity varied by a factor of ten between the highest and lowest polluting power companies. The study concluded that much of the difference in pollution rates is directly attributable to air emission control requirements, which can vary immensely depending upon any specific power plant's vintage and precise location. Many electric generators in the Midwest and Southeast release largely uncontrolled NOx, emissions. Tighter NOx emissions limits prevail in areas currently out of compliance with air quality standards - such as the Eastern U.S. On top of that, disparate air quality regulations allow many older coal-fired generators to emit NOx at a rate five to ten times that of a new coal plant and 20 to 30 times that of a new natural gas electricity generator.

EPA has recently taken several steps to limit NOx emissions from power plants: the issuance of stricter air quality standards for ozone; requirements to retrofit power plants with control technology under provisions of the acid rain program; and a requirement that states contributing to the non-attainment, or interfering with attainment of air quality standards in downwind states, submit new air quality plans focused on limiting interstate pollution. EPA's effort to control the environmental and health effects of ozone has been dealt a setback, however, by the Appellate Court for the District of Columbia, which struck down EPA's revised ozone standard. This decision is being appealed.

How can consumer electricity choice address ground-level ozone?

The advent of competition in the electricity business presents both risks and opportunities for those concerned about the air quality and public health impacts of electricity generation. Competition has already led to increased use of high-polluting coal-fired power plants that are exacerbating the air quality problems outlined above. If concerned about ozone pollution, consumers can "vote" with their pocketbooks and switch to power products consisting of non-polluting renewable energy sources. Even supply portfolios made up, in whole or in part, of electricity generated by traditional fossil-fuels (coal, oil, natural gas) exhibit a wide range of environmental performance. A well-informed consumer would identify and select those electricity suppliers whose sources have taken steps to greatly reduce harmful NOx emissions.


The Energy Project, Land and Water Fund of the Rockies, How the West Can Win: A Blueprint for a Clean and Affordable Energy Future (1996).

ESEERCO, New York State Environmental Externalities Cost Study Vol. 1 (1995).

National Resources Defense Council (NRDC), Benchmarking Air Emissions of 100 Largest Electric Generation Owners in the U.S.

Pace University Center for Environmental Legal Studies, Environmental Costs of Electricity (1990).

Washington University in St. Louis, Effects of Ozone Pollution (last modified Apr. 14, 2000)

Fine Particulates

What are fine particulates?

Particulates are tiny solid or liquid droplets found in the air. These particles come in many shapes and sizes, and from many different sources. Some particles, like soot or smoke, are large or dark enough to be seen by the naked eye. These coarse particles (PM-10) are generally emitted from sources such as road and wind borne dust, materials handling, and crushing and grinding operations. Others are so small they can only be seen with special microscopes. These "fine" particles measure less than 2.5 micrometers in diameter (PM-2.5) -- about the size of bacteria - and are of particular concern because they can be breathed deep into the lungs and generally contain more toxic substances. (see below)

For example, the British Columbia Ministry of Environment reports that a number of harmful substances have been found in PM-2.5. Sulphates produced from sulphur dioxide emissions are acidic in nature and may react directly with the lungs. Carbon produced during wood and engine combustion can pick up cancer-causing chemicals, which are then transported into the lungs. Additionally, toxic trace metals such as lead, cadmium and nickel have been found to be more concentrated in PM-2.5 than in larger particulates. (B.C. Ministry of Environment, "Fine Particulates, What They Are and How They Affect Us", February 1995)

Combustion of fossil fuels is the main source of fine particulate pollution, including the burning of coal, oil, diesel fuel, gasoline, and wood in transportation, power generation and space heating. Old coal-fired power plants, industrial boilers, diesel and gas-powered vehicles, and wood stoves are the worst emitters of fine particulates.

What are the consequences of fine particulate emissions?

Particulates have come to be viewed by health experts and environmental regulators as one of the most serious pollution problems. Particulates inhaled in the respiratory system are directly linked with a number of health effects. Exposure to coarse particles is tied to respiratory conditions such as asthma. More than two dozen community health studies since 1987 have linked particulate matter to reduction in lung function, increased hospital and emergency room admissions, and premature deaths. A 1995 Harvard University study determined that populations exposed to elevated levels of fine particulates had a significantly higher likelihood of premature death than those living in cleaner cities. (Summarized in Center for Clean Air Policy, Air Quality and Electric Utility Restructuring, March 1997.) The Natural Resources Defense Council estimates that at current particulate pollution levels, approximately 64,000 premature deaths from heart and lung disease may be occurring each year. (Natural Resources Defense Council BREATH-TAKING: Premature Mortality Due to Particulate Air Pollution in 239 American Cities, May 1996. Information from this report is available at http://www.nrdc.org/air/pollution/bt/btinx.asp).

Particulates are also a major culprit in reducing visibility. Visibility is caused by the absorption of light by certain particulates (such as soot); and the reflection of light by other forms of particulates (such as sulfates and nitrates). Visibility problems are not confined to urban areas; they are also a major air quality concern in and around national parks and wilderness areas. Moreover, visibility is not only a quality of life issue; it is a vital economic issue for industries dependent upon a pristine environment.

How does electricity production contribute to the health and environmental problems associated with fine particulates?

Electric power production accounts for roughly a quarter (23%) of all particulate matter emitted. Particulate emissions correlates strongly with emissions of the pollutants that contribute to acid rain and smog; namely, sulfur dioxide (SO2) and nitrogen oxides (NOx). (See "Acid rain" and "Ozone" discussion issues). As is the case with these pollutants, coal-fired generation is the power generation technology most strongly associated with particulates. Looking at 26 types of generating technologies, the New York State Energy Office reports extremely high emissions rates for wood waste, residual oil combustion turbines, biomass gasification, and municipal solid waste facilities. (New York State Energy Office, 1994 State Energy Plan, Vol III, p. 621 and fig. 21)

Currently available control technologies can be effective in removing particulate matter that is ten microns and less in diameter. These control measures can remove up to 99 percent of particulate emissions. Unfortunately, these control technologies are not as effective in removing the smaller and generally more harmful fine particles.

How can consumer electricity choice address fine particulates?

As noted above, emissions of fine particulates are strongly connected to certain types of energy production facilities; namely, uncontrolled emissions from coal-fired, oil and many waste-to-energy facilities. More discerning consumers can help clean the air of fine particulates by supporting those forms of generation that are non-polluting such as solar photovoltaics and wind.

A smaller, though still significant bite can be taken out of the particulate problem by supporting less-polluting technologies fueled by natural gas, or those facilities that make an investment in control technology. Power Scorecard can assist in identifying these facilities.

The Energy Project, Land and Water Fund of the Rockies, How the West Can Win: A Blueprint for a Clean and Affordable Energy Future (1996).

ESEERCO, New York State Environmental Externalities Cost Study Vol. 1 (1995).

Pace University Center for Environmental Legal Studies, Environmental Costs of Electricity (1990).

Additional Information:
Natural Resources Defense Council (NRDC) Benchmarking Air Emissions of the 100 Largest Electric Generation Owners in the US http://www.nrdc.org/air/energy/util/index.asp

Natural Resources Defense Council (NRDC) BREATH-TAKING: Premature Mortality Due to Particulate Air Pollution in 239 American Cities, summary

Washington University in St. Louis, Effects of Ozone Pollution http://www.so.wustl.edu/science_outreach/curriculum/ozone/info/troposphere/health.html

Government of British Columbia Ministry of Water, Land and Air Protection Fine Particulates: What they are and how they affect us http://wlapwww.gov.bc.ca/air/particulates/fpwtaaht.html

EPA's Summary of Air Quality and Emission Trends http://www.epa.gov/air/aqtrnd97/brochure/summ.html

Center for Clean Air Policy/Air Quality Program http://www.ccap.org/

http://www.nrdc.org/air/pollution/qbreath.asp#health - This NRDC web page provides answers to "Frequently Asked Questions" about the effects of particulate pollution.

http://www.texaslung.org/educationalresources/factsheets/particlepollution.htm -- This American Lung Association of Texas web page provides a Fact Sheet summary of the health effects of particulate pollution. April 2004

(Revised August, 2004)

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