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Air Quality


"Remember when atmospheric contaminants were romantically called stardust?"
Lane Olinghouse

Events in the Quest for Cleaner Air
What is Air Pollution?
Page 1
The 1990 Federal Clean Air Act
Market Incentives in Texas
Page 2
National Ambient Air Quality Standards
  1. Ozone
  2. Sulfur Dioxide and Nitrogen Oxides - The Building Blocks of Acid Rain
  3. Carbon Monoxide
  4. Particulate Matter
  5. Lead
Do Trees Pollute?
Air Quality Monitoring: How much do we know?
Page 3
Federal Clean Air Act Compliance in Texas
Achieving Clean Air is a Binational Problem for El Paso
Page 4
Page 5
Page 6
Page 7
Page 8

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Texas Environmental Almanac, Chapter 6, Air Quality, Page 1
Air pollution can be hazardous to human health. When people breathe dirty air, pollutants may come into direct contact with their lungs. Polluted air can burn eyes, irritate throats and affect breathing. Some chemicals emitted to the air can cause adverse health effects if released in large enough quantities or over a long enough time. These health effects could include cancer, birth defects, damage to the brain, nervous system or respiratory tract and even, in rare instances, death.(1)

Air pollution also threatens plants, animals and the natural environment. Acid rain can destroy lakes, rivers and the organisms that inhabit them. Certain compounds degrade the ozone layer above the earth, which serves as a filter for the sun's harmful ultraviolet rays. The thinning of this upper level atmospheric ozone layer may lead to higher rates of skin cancer and eye damage for both humans and animals. Other pollutants may stunt the growth of trees and vegetation, including agricultural crops, while increased carbon dioxide levels have been found to actually stimulate plant growth, emphasizing the complexity of air pollution problems.

Common air pollutants can also damage property, dirtying buildings and corroding monuments and statues. And the haze produced by air pollution can reduce visibility, affecting a number of activities including airplane transportation and tourism.

The first efforts to deal legislatively with visible air pollution were directed at smoke emissions from steam boilers. Cincinnati and Chicago passed smoke regulations in 1881; Ohio passed a law to limit these emissions in 1897. It wasn't until the 1940s, however, that new designs which reduced black smoke and saved fuel were phased into factories.(2) Much less effort was directed at controlling the grime and pollutants generated by oil and gas refineries, factory smokestacks, coal-burning locomotives and automobiles.

By the 1960s, new concerns were being raised about urban "smog." Smog is a haze made up of thousands of different compounds. Ozone is its most well known constituent. In fact, excessive ground level ozone is the most pervasive air pollution problem in the U.S., creating both health and environmental effects.

It may seem strange that too little ozone in the upper atmosphere is a problem while too much ozone on ground level is also a problem. However, these types of seeming contradictions are part and parcel of the interrelated air pollution control problems facing us today (see "What is Air Pollution?").

Smog and other air pollutants are particularly damaging when "trapped" at ground level. This may happen in areas that have experienced a temperature inversion, a meteorological phenomenon in which a warm layer of air lies under a cooler, denser layer. A temperature inversion creates a kind of atmospheric blanket that can prevent pollutants generated on the ground from escaping into the upper atmosphere. When a temperature inversion lingers in an area and winds are calm, air pollutants become concentrated. The results can be deadly; in 1948, a temperature inversion over the Pennsylvania town of Donora resulted in the deaths of 20 people and hospitalized hundreds when sulfur, ozone and air particulates were trapped at ground level.(3)

In the wake of the Donora incident, Congress passed a series of bills to study and research the problem of air pollution. But it was not until the 1960 presidential campaign that political leaders began calling for a coordinated, national approach to the problem of air pollution. This concern over air pollution was focused first on the most visible forms of air pollution: smoke, smog and haze. Gradually, legislation has come to address less visible air pollution problems, such as toxic compounds, as well.


The following mark significant air pollution events and important steps taken to prevent their recurrence:


What is Air Pollution?
There are many different aspects of air pollution. Whether the pollution is likely to cause environmental or health effects depends on the concentration of pollutants and the amount of time an individual or other receptor is exposed to them.

Smog is an often visible haze made up of thousands of constituents, the most abundant, but not necessarily the most toxic of which is ozone. Ozone, especially at elevated levels, can create breathing problems particularly in the young, the old and persons with existing health problems by reducing lung function, increasing sensitivity to asthma and aging lung tissue. It is suspected to irritate the eyes, cause nasal congestion and reduce resistance to colds and other infections. Ozone at elevated levels is toxic to other living organisms as well; it damages plants and trees by affecting the stability of cell walls.

Particulate matter, produced by the burning of wood, diesel and other fuels, by agricultural activities and industrial processes and by traffic on unpaved roads, is made up of ash, smoke, soot, dust, fibers and liquid droplets. Particulate matter produces a haze that can cause visibility problems. It also dirties and damages buildings and clothes. Smaller particulates, which float in the air, can be inhaled deeply and, with elevated concentrations over an extended period of time, can cause lung damage and bronchitis. Recent studies have linked exposure to these smallest particles to a greater risk of premature death.(5)

Nitrogen oxides result from the burning of fossil fuels like coal, natural gas, gasoline and oil. At present, automobiles are the main source of nitrogen oxide emissions in urban areas. Nitrogen oxides, at elevated concentrations, can damage the respiratory system. They also can be a key ingredient in the formation of both ozone and acid rain.

Sulfur dioxide is released when sulfur-containing fuels like coal and oil are burned. Common sources of sulfur dioxide emissions are electric utilities and certain industrial processes. Sulfur dioxide at elevated concentrations can cause respiratory problems. It also can be a contributing component of acid rain.

Toxic chemicals such as benzene, toluene and 1,1,1 trichloroethane, when present in the air that we breathe in elevated concentrations over time, can cause various health effects including birth defects, cancer and other health problems. Sources of toxic emissions include industrial processes, such as refineries and chemical manufacturers, small businesses such as printers and dry cleaners and automobiles.

Carbon Monoxide (CO) is formed when fuel does not burn completely. Cars and trucks are the main contributors. Carbon monoxide interferes with the blood's ability to transport oxygen to cells and tissues. Exposure to elevated levels of carbon monoxide can cause drowsiness, headaches and sometimes death. Carbon monoxide is particularly hazardous to those who have heart disease or pre-existing lung conditions.

Lead is a heavy metal that persists in the environment for decades. The former use of leaded gasoline, which is no longer commercially available in most of the United States, the manufacture of lead-based paint and lead-acid battery reclamation operations are sources of lead in the air. Emissions from metal smelters are another source. Exposure to lead at high levels and over time can cause brain and other nervous system damage, particularly in children. Excess exposure to lead can also harm wildlife and is known to cause cancer in animals.

Acid Rain forms when the sulfur dioxide, nitrogen oxides and carbon dioxide emitted from fossil fuel-burning plants and other combustion processes combine with rain, fog or snow in the atmosphere. Over time, with conducive geologic conditions, acid rain can increase the acidities of lakes, streams and soils, disturbing or destroying local environments. Wind can carry pollutants far away from where they originated, creating problems in other states or countries.

Source: Environmental Protection Agency, The Clean Air Act Amendments: A Guide for Small Businesses (Washington, DC: EPA, September 1992).

Texas Environmental Almanac, Chapter 6, Air Quality, Page 1

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