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The EPA Office of Air Quality Planning and Standards has set National Ambient Air Quality Standards for six principal pollutants, referred to as "criteria" pollutants. (This table identifies eight pollutants, because we have divided "Particulate Matter" into three categories.) The federal air quality standards are usually also adopted as State air quality standards. Units of measure for the standards are parts per million by volume (ppm), parts per billion by volume (ppb), milligrams per cubic meter of air (mg/m3), or micrograms per cubic meter of air (µg/m3), exposed for durations of between 1 hour and 24 hours. Statistical Summary entries are calendar-year annual statistics, except as noted. Historical standards discontinued before 2006 by both EPA and NC are not included.
| Pollutant |
Threshold Level |
Sample Aggregation |
Statistical Summary |
Effective Date |
Health Standard |
Secondary Standard |
State Standard |
| Carbon Monoxide |
9 ppm-8 hr
(10 mg/m3-8 hr) |
Annual |
Extreme(1) |
1971 |
Yes |
n/a |
Yes |
35 ppm-1 hr
(40 mg/m3-1 hr) |
Annual |
Extreme(1) |
1971 |
Yes |
n/a |
Yes |
| Lead |
0.15 µg/m3-24 hr |
Monthly |
Extreme(2) |
2009 |
Yes |
Yes |
Yes |
| 1.5 µg/m3-24 hr |
Quarterly |
Arith. Mean |
1978 |
Yes |
Yes |
No |
| Nitrogen Dioxide |
0.053 ppm-1 hr
(100 µg/m3-1 hr) |
Annual |
Arith. Mean |
1971 |
Yes |
Yes |
Yes |
| 100 ppb-1 hr |
Annual |
Extreme(3) |
2010 |
Yes |
No |
Yes |
| Total Suspended Particulates |
75 µg/m3-24 hr |
Annual |
Geom. Mean |
1971 |
No(4) |
No(4) |
Yes |
| 150 µg/m3-24 hr |
Annual |
Extreme(5) |
1971 |
No(4) |
No(4) |
Yes |
| Particulate Matter (PM10) |
150 µg/m3-24 hr |
Annual |
Extreme(5) |
2006 |
Yes |
Yes |
Yes |
| Particulate Matter (PM2.5) |
12.0 µg/m3-24 hr
|
Quarterly |
Arith. Mean(6) |
2013 |
Yes |
No |
Yes |
15.0 µg/m3-24 hr
|
Quarterly |
Arith. Mean(6) |
2006 |
No |
Yes |
No |
| 35 µg/m3-24 hr |
Annual |
Extreme(7) |
2006 |
Yes |
Yes |
Yes |
| Ozone |
0.075 ppm-8 hr |
Annual(8) |
Extreme(9) |
2008 |
Yes |
Yes |
Yes |
| 0.12 ppm-1 hr |
Annual(8) |
Extreme(10) |
2005 |
No(11) |
No(11) |
No |
| Sulfur Dioxide |
75 ppb-1 hr |
Annual |
Extreme(12) |
2010 |
Yes |
No |
Yes |
| 0.03 ppm-1 hr |
Annual |
Arith. Mean |
1971 |
No(13) |
No |
Yes |
| 0.14 ppm-24 hr |
Annual |
Extreme(1) |
1971 |
No(13) |
No |
Yes |
0.5 ppm-3 hr
(1300 µg/m3-3 hr) |
Annual |
Extreme(1) |
1971 |
No |
Yes |
Yes |
- Not to be exceeded more than once per year.
- The 3-year average of annual maximum 3-month moving averages must not exceed the threshold.
- The 3-year average of ninety-eighth percentile daily maximums must not exceed the threshold.
- The USEPA discontinued the TSP standard in 1987 and replaced it with a like standard for PM10.
- Not to be exceeded more than once per year on average for 3 years.
- The 3-year average from single or multiple community-oriented monitors must not exceed the threshold.
- Ninety-eighth percentile. The 3-year average at each population-oriented monitor within an area must not exceed the threshold.
- Certain months are exempted in many areas (specif., November through March in North Carolina).
- Fourth-largest daily maximum. The 3-year average at each monitor within an area over each year must not exceed the threshold.
- Largest daily maximum. The 3-year average at each monitor within an area over each year must not exceed the threshold.
- As of June 15, 2005 the USEPA revoked the standard in all areas except fourteen 8-hour ozone nonattainment Early Action Compact (EAC) Areas. The standard was revoked for the various EAC areas piecemeal on either Nov. 20, 2007; Nov. 20, 2008; or April 15, 2009.
- The 3-year average of ninety-ninth percentile daily maximums must not exceed the threshold.
- The USEPA revoked this standard in 2010 in acknowledgement that the new primary standard is generally sufficient to protect the 1971 primary standards from being violated.
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