Air Quality Pollutants and Standards

​Carbon Monoxide (CO)

Carbon monoxide (CO) is a colorless, odorless gas emitted directly from motor vehicles, off-road equipment, and other sources of equipment powered by fossil-fuels. High CO concentrations are a health concern because the pollutant is readily absorbed through the lungs into the blood, where it binds with hemoglobin and reduces the ability of the blood to carry oxygen.

The Sac Metro Air District measures CO concentrations at multiple monitoring stations. More information on the location of carbon monoxide monitors and monitors for other pollutants can be found on the Air Monitoring page.

Footnote:

1 The original NAAQS was established in 1971.  EPA reviewed both the 1-hour and 8-hour standards and decided to retain these standards in 2011.

​Lead (Pb)

Lead (Pb) is a naturally occurring element in the environment and may also be a byproduct of industrial processes. Lead affects many different areas of the brain, nervous system, kidney function, immune system, reproductive and developmental systems, and the cardiovascular system. In children, even low levels of lead exposure has been associated with reduced IQ, learning disabilities, decreased growth, hyperactive and antisocial behavior, and impaired hearing.

The Sac Metro Air District measures lead at one monitoring station. More information on the lead monitor and other monitors can be found on the Air Monitoring page.

​Nitrogen Dioxide (NO₂)

Nitrogen dioxide (NO2) is one of a group of highly reactive gases known as nitrogen oxides (NOX). NO2 forms quickly from emissions from cars, trucks and buses, power plants, off-road equipment and other combustion sources. In addition to contributing to the formation of ground-level ozone and fine particle pollution, NO2 is associated with a number of adverse effects on the human respiratory system.

People who spend time on or near major roadways can experience short-term NO2 exposures considerably higher than the concentrations measured at ambient air monitoring stations. Exposure to elevated NO2 concentrations near roadways is of particular concern for susceptible people, including those with asthma, children, and the elderly. The Sac Metro Air District currently operates one NO2 near-road monitor and the need for a second monitor is being evaluated. A map showing the location of this monitor and others can be found on the Air Monitoring page.

In 2010, EPA set the new one-hour average standard for NO2 at a level of 100 parts per billion (ppb) and retained the existing annual average standard of 53 ppb. The region was designated as attainment in February 2012 for both of these standards.

Footnotes:

1 The original NAAQS were established in 1971.  EPA reviewed and decided to retain the annual arithmetic mean standard in 2010.

2 EPA designates areas as "unclassifiable/attainment" if they met the standard or are expected to meet the standard despite a lack of monitoring data.

​Ozone (O₃)

Ozone (O3) is a gas whose molecules are composed of three oxygen atoms. Ozone is not emitted directly into the air, but is created by a chemical reaction between two precursors — oxides of nitrogen (NO_X) and volatile organic compounds (VOC) — in the presence of sunlight. Ozone concentrations are expressed in parts per million (ppm) or parts per billion (ppb). High ground-level ozone concentrations can reduce lung function and increase respiratory symptoms, thereby aggravating asthma, bronchitis, or other respiratory conditions including chest pains and wheezing. Ozone exposure is associated with increased susceptibility to respiratory infections, cardiac-related effects, medical visits, school absenteeism and contributing to premature death, especially in people with heart and lung disease.

 Reducing ozone to levels below state and federal standards is one of the primary goals of the Sac Metro Air District . As a nonattainment area, the region must evaluate air quality data and emission trends to determine how much ozone concentrations will need to be reduced to attain the standard in the future. Control measures and strategies are included as commitments in these plans to achieve the reductions in emissions of NOx and VOC necessary for the region to attain the standard. Information on the location of ozone monitors can be found on the Air Monitoring page.

Footnotes:

1 EPA revoked the 1979 1-hour and 1997 8-hour standards.

2 EPA issued Determination of Attainment on Oct 18, 2012 (77 FR 64036) but the Sacramento Federal Ozone Nonattainment Area has not yet redesignated the  to Attainment.

³ The nonattainment area is classified as Severe-15.

4 In April 2005, the California Air Resources Board (CARB) approved a new 8-hour standard of 70 ppb and retained the 1-hour standard of 90 ppb.

5 The nonattainment area is classified as Moderate for the 2015 NAAQS of 70 ppb (83 FR 25788).

​Particulate Matter (PM)

Particulate matter (PM) is a mixture of solid and liquid particles, and is measured and expressed as the mass of particles, in micrograms, per cubic meter of air (μg/m3). Because particles originate from a variety of activities and processes, their chemical and physical compositions vary. PM can be emitted directly or produced by secondary formation in the atmosphere when gaseous pollutants, such as nitrogen oxides and sulfur dioxide, chemically react with ammonia and other compounds to form fine aerosol particles. Elevated levels of particulate matter can cause adverse human health effects, including reduced lung function, increased respiratory complications, cardiovascular disease, and increased risk of cancer. People most affected are those with influenza and asthma. 

PM pollution is caused mainly by human (anthropogenic) activities, such as residential wood burning, road dust, on-road and off-road vehicles, construction, and farming activities. PM can also be generated from natural sources such as windblown dust and wildfires.  More information on the particulate matter monitors can be found on the Air Monitoring page.

Air quality standards for PM are based on particle size:

• PM2.5 standards consist of particles 2.5 microns in diameter or less (fine and ultra-fine particles); and

• PM10 standards consist of particles 10 microns in diameter or less (coarse particles).

Particulate Matter - 2.5 microns (PM2.5)

Footnote:

¹ EPA issued Determination of Attainment on May 10, 2017 (82 FR 21711) but the Sacramento Federal PM_2.5 Nonattainment Area has not yet redesignated the  to Attainment.

Particulate Matter - 10 microns (PM10)

​Sulfur Dioxide (SO₂)

Sulfur dioxide (SO2) is a highly reactive gas, and the largest sources of SO2 emissions are power plants and other industrial facilities that combust fossil fuels. Smaller sources of SO2 emissions include the burning of high sulfur-containing fuels by locomotives and non-road equipment, and non-combustion industrial processes, such as extracting metal from ore. SO2 is linked with a number of adverse effects on the respiratory system.

In 2010, EPA revised the primary SO2 NAAQS by establishing a new 1-hour standard at a level of 75 parts per billion (ppb). The Sac Metro Air District has one monitor that measures sulfur dioxide. The region is currently in attainment for the standard. More information on the sulfur dioxide monitor and other monitors can be found on the Air Monitoring page.

1 Attainment /Unclassifiable designation was made as par of EPA's Air Quality Designations for the 2010 Sulfur Dioxide (SO₂) Primary National Ambient Air Quality Standard - Round 3 designation in December  2017.