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EPA Defines Air Pollution Danger Levels

[EPA press release - October 19, 1971]

The Environmental Protection Agency today defined, for five of the most common air contaminants, the levels at which "significant harm" to the health of persons might occur during episodes of high air pollution.

The five pollutants are sulfur dioxide, particulate matter, carbon monoxide, photochemical oxidants, and nitrogen dioxide.

The danger levels were stipulated in an amendment to regulations, issued by the EPA on August 14, 1971, to guide States in planning to clean the Nation's air to healthful levels by mid-1975. These regulations require each State plan to spell out steps to be taken to prevent episodes of dangerously high air pollution. Such steps would become progressively more stringent as air pollution concentrations increased toward the danger points.

The EPA emphasized that State action should assure that air pollution never reaches the levels at which significant harm to health may occur. Under the Clean Air Act, the Administrator of the Environmental Protection Agency is empowered to bring suit on behalf of the United States in a Federal district court when air pollution presents an imminent and substantial endangerment to the health of persons.

NOTE: A table showing the danger levels is attached.


Air Pollution Levels That Could Cause Significant Harm to the Health of Persons

Sulfur dioxide
2620 micrograms/cubic meter (1.0 part per million), 24-hour average

Particulate matter
1,000 micrograms/cubic meter or 8 COHs, 24-hour average

Sulfur dioxide and particulate matter combined
product of sulfur dioxide in micrograms/cubic meter, 24-hour average, and particulate matter in micrograms/cubic meter, 24-hour average, equal to 490 x 103 or product of sulfur dioxide in parts per million, 24-hour average and COHs, 24-hour average, equal to 1.5

Carbon monoxide
57.5 milligrams/cubic meter (50 parts per million), 8-hour average

  • 86.3 milligrams/cubic meter (75 parts per million), 4-hour average
  • 144 milligrams/cubic meter (125 parts per million), 1-hour average

Photochemical oxidants
800 micrograms/cubic meter (0.4 part per million), 4-hour average

  • 1,200 micrograms/cubic meter (0.6 part per million), 2-hour average
  • 1,400 micrograms/cubic meter (0.7 part per million), 1-hour average

Nitrogen dioxide
3,750 micrograms/cubic meter (2.0 parts per million), 1-hour average

  • 938 micrograms/cubic meter (0.5 part per million), 24-hour average