Environmental Services Program
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 or 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 or CO
- Lead or Pb
- Nitrogen Dioxide or NO2
- Ozone or O3
- Sulfur Dioxide or SO2
- Inhalable Particulates or PM10
- Fine Inhalable Particulates or PM2.5
- 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.
| 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
- 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.
| Averaging Time | Primary Standard | Secondary Standard |
|---|---|---|
| Three-month (Rolling average) | 0.15 ug/m3 | Same as Primary |
| Quarterly Average | 1.5 ug/m3 | Same as Primary |
- 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.
| Averaging Time | Primary Standard | Secondary Standard |
|---|---|---|
| One-year | 53 ppb | Same as Primary |
| One-hour | 100 ppb | None |
The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which is shown here for the purpose of clearer comparison to the 1-hour standard.
The one-hour standard is a 3-year average of the 98th percentile of the daily maximum 1-hour average at each monitor within an area must not exceed 100 ppb (effective January 22, 2010).
- 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.
| Averaging Time | Primary Standard | Secondary Standard |
|---|---|---|
| Eight-hour (standards) | 0.075 ppm | 0.075 ppm |
- 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.
| Averaging Time | Primary Standard | Secondary Standard |
|---|---|---|
| 24-hour | 0.14 ppm | None |
| One-year | 0.03 ppm | None |
| One-hour/Three-year | 75 ppb | None |
To attain the one-hour/three-year standard, the 3-year average of the 99th percentile of the daily maximum 1-hour average at each monitor within an area must not exceed 75 ppb.
6. Inhalable Particulates or 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.
| Averaging Time | Primary Standard | Secondary Standard |
|---|---|---|
| 24-hour (standards) | 150 ug/m3 | 150 ug/m3 |
7. Fine Inhalable Particulates or 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.
| 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
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