Air Quality Standards

The U.S. National Ambient Air Quality Standards (NAAQS) are limits for six pollutants that cause smog, acid rain, and other health hazards. They’re set by the EPA and applicable to every county in every state throughout the country.

Ozone (O3)

Ozone is odorless and colorless gas made up of three oxygen atoms. It is the same chemical structure whether in the upper atmosphere of the earth or at ground level. At ground-level, however, it is unnaturally formed and can be damaging to people, animals and plants. Groundlevel ozone is also the standard most challenging for the Tulsa region to meet.

Unhealthy ozone concentrations aren’t directly emitted in the air, but occur when emissions mix. In strong sunlight and heat, the oxides of nitrogen (NOx) and volatile organic compounds (VOCs) emissions from sources like vehicle exhaust, industrial emissions, gasoline vapors, chemical solvents and even natural sources, undergo a chemical reaction – and ozone is formed. Ozone’s chemical bond is fairly unstable, needing the heat and sunlight to ‘force’ the bond. High concentrations generally can’t occur on windy, cool and overcast days. And evening and overnight hours of post-sundown lets the unstable ozone break apart and dissipate. This is why ground-level ozone is mainly a summertime problem.

The national primary and secondary ambient air quality standard for ozone is 0.070 ppm. These standards are met when the average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.070 ppm using the most recent 3 years of collected data at any one ozone monitoring site. The primary standards are designed to protect public health, including the health of sensitive populations such as asthmatics, children and the elderly. The secondary standards are designed to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation and buildings.

Particulate Matter (PM2.5)

Particle pollution (also known as “particulate matter”) consists of a mixture of solids and liquid droplets. Some particles are emitted directly; others form when pollutants emitted by various sources react in the atmosphere. Particle pollution levels can be very unhealthy and even hazardous during events such as forest fires. Particle levels can be elevated indoors, especially when outdoor particle levels are high.

Particles come in a wide range of sizes. Those less than 10 micrometers in diameter (smaller than the width of a single human hair) are so small that they can get into the lungs, where they can cause serious health problems.

  • Fine particles. The smallest particles (those 2.5 micrometers or less in diameter) are called “fine” particles. These particles are about 3% the diameter of a human hair, so small they can be detected only with an electron microscope. Major sources of fine particles include motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, some industrial processes, and other combustion processes.
  • Coarse particles. Particles between 2.5 and 10 micrometers in diameter are referred to as “coarse.” Sources of coarse particles include crushing or grinding operations, and dust stirred up by vehicles traveling on roads.

There are three EPA standards for PM-2.5: 1)A primary standard of an annual arithmetic mean of 12 micrograms per cubic meter (μg/m3 ), 2) A secondary standard of 15 μg/m3 (annual arithmetic mean), and 3) A 24-hour average not to exceed 35 μg/m3 . For PM-10, the primary and secondary standard is a 24-hour average of 150 μg/m3. Meeting the standard is based on an average of three calendar years of data. The 24-hour PM-2.5 standards are met when the three-year expected number of exceedances per year at each monitoring site is less than or equal to one. The annual standard is met when the three-year expected number of exceedances per year at each monitoring site is less than or equal to one. The annual standard is met when the three-year expected annual arithmetic mean is less than or equal to the standard.

Carbon Monoxide (CO)

Carbon monoxide (CO) is a colorless, odorless, tasteless, poisonous gas. It occurs naturally in the air from agricultural fires, oxidation of methane, plant growth and decay and other natural processes. CO is a byproduct formed when carbon in fuels is not completely burned. The urban atmosphere contains 100 times as much CO as any other pollutant. While it is the most abundant pollutant in urban air, the accumulation of numerous other pollutants may be more hazardous even in comparatively lower concentrations. The high concentration of urban CO is produced primarily by motor vehicles. CO is also released by some industrial processes and inhome activities. Since motor vehicles are the major source of CO, daily concentration peaks coincide with morning and evening rush hours when city traffic is heaviest. Other sources include fuel combustion in industrial processes and natural sources such as wildfires.

EPA has two national ambient air quality primary standards for CO: 35 parts per million (ppm) averaged over a 1- hour period and 9 ppm averaged over an 8-hour period. For the EPA to consider an area in compliance with the standard, these values may be exceeded only once in a given year. Once an air quality monitor measures a second exceedance of either standard in a calendar year, a violation of the standard has occurred.

Sulfur Dioxide (SO2)

Sulfur dioxide, a colorless, reactive gas, is produced when sulfur-containing fuels such as coal and oil are burned. Generally, the highest levels of sulfur dioxide are found near large industrial complexes. Major sources include power plants, refineries and industrial boilers.

There are two National Ambient Air Quality Standards (NAAQS) for SO2 : The primary standard is a one-hour average of 75 parts per billion (ppb); and the secondary standard is a three-hour average of 0.50 ppm. To meet the standard, the 3-year average of annual 99th percentile one hour average daily maximum concentrations must not exceed 75 ppb. The secondary standard must not be exceeded more than once per year.

Nitrogen Dioxide (NO2)

Nitrogen Dioxide (NO2) is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. NO2 is used as the indicator for the larger group of nitrogen oxides.

NO2 primarily gets in the air from the burning of fuel. NO2 forms from emissions from cars, trucks and buses, power plants and off-road equipment.

There are two primary National Ambient Air Quality Standards (NAAQS) for NO2 : The 1-hour NO2 standard of 100 parts per billion (ppb), as determined by the three-year average of the 98th percentile of the annual distribution of daily maximum 1-hour average concentrations 2; and the annual arithmetic mean of 0.053 ppm of NO2.

Lead (Pb)

Elemental lead (Pb) is a heavy, soft, bluish metal that occurs in nature in the form of ores. Lead in the ambient air exists primarily as lead vapors, very fine particles, and organic halogens like lead bromide and lead chloride. Common sources that emit lead to the atmosphere are fuel additives, nonferrous smelting plants, and battery and ammunition manufacturing. In 1985, motor vehicle emissions accounted for 81 percent of lead emissions nationwide. Today however, lead is banned from use in gasoline. Lead emissions from industry have also been substantially reduced through control programs aimed toward attainment of the particulate matter and lead ambient air quality standards.

For lead, there are identical primary and secondary National Ambient Air Quality Standards (NAAQS) of 0.15 micrograms per cubic meter (μg/m3 ) measured on a 3-month rolling average. The primary and secondary standards are measured as total suspended particles (TSP) collected on a filter.

National Ambient Air Quality Standards (NAAQS)

The National Ambient Air Quality Standards (NAAQS) define the maximum permissible concentrations for certain pollutants, known as criteria pollutants. Click on the pollutant name for the relevant DEQ factsheet.

Pollutant Standard Averaging Time Level Form
Carbon Monoxide (CO) Primary 8-hour 9 ppm Not to be exceeded more than once per year
1-hour 35 ppm
Lead (Pb) Primary and Secondary Rolling 3-month average 0.15 μg/m3 Not to be exceeded
Nitrogen Dioxide (NO2) Primary 1-hour 100 ppb 98th percentile of 1-hour daily maximum concentrations, averaged over 3 years
Primary and Secondary Annual 53 ppb Annual Mean
Ozone (O3) Primary and Secondary 8-hour 0.070 ppm Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years
Particulate Matter PM2.5 Primary Annual 12 μg/m3 annual mean, averaged over 3 years
Secondary Annual 15 μg/m3 annual mean, averaged over 3 years
Primary and Secondary 24-hour 35 μg/m3 98th percentile, averaged over 3 years
PM10 Primary and Secondary 24-hour 150 μg/m3 Not to be exceeded more than once per year on average over 3 years
Sulfur Dioxide (SO2) Primary 1-hour 75 ppb 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
Secondary 3-hour 0.5 ppm Not to be exceeded more than once per year