National Ambient Air Quality Standards

The air quality of outdoor air breathed by the public is determined by carefully comparing the monitored level of air pollutants with air quality standards established by the U.S. Environmental Protection Agency (EPA). The National Ambient Air Quality Standards set the limits for seven air pollutants that have documented effects on public health.

The National Ambient Air Quality Standards contain primary and secondary standards for each of these seven air pollutants. If a primary standard is exceeded, health risks exist. If a secondary standard is exceeded, then crops, trees and buildings may be damaged.

Most of the air quality standards are based on a particular time length for averaging, and the average concentration during that time. For a violation to be recorded the average concentration, usually rounded to the same number of significant digits as the standard, must be greater than the standard during the specified averaging period.

Carbon Monoxide (CO)
Lead (Pb)
Nitrogen Dioxide (NO2)
Ozone (O3)
Sulfur Dioxide (SO2)
Inhalable Particulates (PM10)
Fine Inhalable Particulates (PM2.5)

1. Carbon Monoxide (CO)

Characteristics: A poisonous gas that is odorless, colorless and tasteless.
Health effects: Headache, mental dullness, dizziness, weakness, nausea, vomiting, loss of muscular control, increased then decreased pulse and respiratory rates, collapse or unconsciousness.

CARBON MONOXIDE STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
One-hour	35 ppm	none
Eight-hour	9 ppm	none

Neither standard is allowed to be exceeded more than once per year

2. Lead (Pb)

Characteristics: A bluish-white, silvery-gray solid. Lead particulates look like dust, ranging from black to lighter shades of gray.
Health effects: Decreased physical fitness, fatigue, sleep disturbance, headache, aching bones and muscles, constipation, abdominal pains and decreased appetite. High levels of exposure can also result in permanent nervous system damage, seizures, coma and death.

LEAD STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
Three-month (Rolling average)	0.15 ug/m³	1.5 ug/m ³

3. Nitrogen Dioxide (NO2)

Characteristics: A poisonous, reddish-brown to dark brown gas with an irritating odor.
Health effects: Nose and throat irritation, coughing, choking, headache, nausea, stomach or chest pains and lung inflammation such as bronchitis or pneumonia.

NITROGEN DIOXIDE STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
One-year	0.053 ppm	0.053 ppm

4. Ozone (O3)

Characteristics: A bluish, explosive gas that has a pleasant odor when the concentration is less than 2 parts per million (ppm).
Health effects: Coughing, chest discomfort, decreased pulmonary functions, respiratory tract and eye irritation.

OZONE STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
Eight-hour (standards)	0.075 ppm	0.075 ppm

5. Sulfur Dioxide (SO2)

Characteristics: A colorless gas with a strong, suffocating odor.
Health effects: Throat and lung irritation, swelling and accumulation of fluid in throat and lungs or nasal bleeding.

SULFUR DIOXIDE STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
24-hour	0.14 ppm	none
One-year	0.03 ppm	none
Three-hour	none	0.50 ppm

6. Inhalable Particulates (PM10)

Characteristics: A broad class of chemically and physically diverse substances that exist as particles with a diameter less than or equal to 10 microns.
Health effects: Inhalation of particulates increases chronic and acute respiratory illnesses.

INHALABLE PARTICULATES(PM10) STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
24-hour (standards)	150 ug/m³	150 ug/m³

7. Fine Inhalable Particulates (PM2.5)

Characteristics: A broad class of chemically and physically diverse substances that exist as particles with a diameter less than or equal to 2.5 microns.
Health effects: Inhalation of particulates increases chronic and acute respiratory illnesses.

FINE INHALABLE PARTICULATES(PM2.5) STANDARDS
AVERAGING TIME	PRIMARY STANDARD	SECONDARY STANDARD
One-year (standards)	15.0 ug/m³	15.0 ug/m³
24-hour	35 ug/m³	35 ug/m³

For more information about the pollutants and thier standards please visit, http://www.epa.gov/air/criteria.html