Air Pollutants

​Common air pollutants with known health impacts were first regulated as “Criteria Pollutants” by the 1970 Clean Air Act which established health-based National Ambient Air Quality Standards (NAAQS). The six criteria pollutants are carbon monoxide, ground-level ozone, lead, nitrogen dioxide, particulate matter, and sulfur dioxide. 

Criteria pollutants are measured using the Mecklenburg County ambient air monitoring network. The information gathered is used to help determine if our local air quality attains the federal health-based NAAQS, as shown below. Visit the Air Quality Monitoring website to access current criteria pollutant data. 

Mecklenburg County currently meets all federal, health-based air quality standards. 
PollutantAveraging TimeMecklenburg Compliance Value (2023)NAAQSFederal NAAQS Designation
Ozone (O3)8-hour

69 ppb

70 ppb

Particulate Matter (PM2.5)24-hour

21 μg/m3

35 μg/m3


9.2 μg/m3

12 μg/m3

Particulate Matter (PM10)24-hour

50 μg/m3

150 μg/m3

Carbon Monoxide (CO)8-hour

1.6 ppm

9 ppm


2.0 ppm

35 ppm

Sulfur Dioxide (SO2)1-hour

2 ppb

75 ppb


0.004 ppm

0.5 ppm

Nitrogen Dioxide (NO2)1-hour

37 ppb

100 ppb


10.7 ppb

53 ppb

*Other common pollutant not listed above is lead (Pb).

Definition of Terms

Ground-level Ozone (O3)

Ground-level ozone concentrations are improving in Mecklenburg County. On November 6, 2017, the United States Environmental Protection Agency (EPA) announced it will designate Mecklenburg County, along with all counties in North Carolina and South Carolina,  as "attainment" for the new ozone standard.  In 2015, EPA lowered the ozone standard from 75 ppb to 70 ppb to be more protective of public health.  

Ground-level ozone, the primary constituent of smog, is not emitted directly into the air but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone forms most efficiently during summer months when days are longer, the sunlight is stronger, and when temperatures are warmest. Daily ozone levels peak in the warmest part of the day, during mid-afternoon through evening.


Mobile sources of air pollution (e.g. passenger vehicles, transit trucks, construction equipment, etc.) emit nearly 90% of all NOx emissions and 50% of VOC emissions in Mecklenburg County. Find tips to REDU​CE OZONE pollution.

Breathing ozone can reduce lung function and inflame the linings of the lungs triggering a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can also worsen pre-existing conditions like bronchitis, emphysema, and asthma. Repeated exposure may permanently scar lung tissue. People with lung disease, older adults, people who are active outdoors, and especially children, may be particularly sensitive to ozone. It is safer on forecasted high ozone days to exercise or perform strenuous outdoor activities in the morning.

Learn more about Ground-level Ozone at

Particulate Matter (PM)

Mecklenburg County is in compliance with National Ambient Air Quality Standards for particulate matter and measured concentrations continue to decrease.

 Particulate Matter, also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Sources of particle pollution can come from human made sources such as charbroiling, construction equipment, trains, vehicle exhausts, and many more. In addition, there are natural sources of PM pollution like pollen, wildfires, dust, sea salt, and volcano eruptions.

The size of particles is directly linked to their potential for causing health problems. Particles that are 10 micrometers in diameter or smaller (less than 1/5th the diameter of a human hair) are of particular concern because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

-PM 10 or "Inhalable coarse particles," such as those found near roadways and dusty industries, are smaller than 10 micrometers in diameter.

-PM 2.5 or "Fine particles," such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller (less than 1/30th the diameter of a human hair). These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.

More information can be found at

Illustration demonstrating the size of air particulates being smaller than diameter of human hair or grains of sand.

Carbon Monoxide (CO)

Mecklenburg County is currently in compliance with National Ambient Air Quality Standard for carbon monoxide (CO).

CO is a colorless, odorless gas produced by the incomplete combustion of fossil fuels primarily from mobile sources of air pollution (i.e. passenger vehicles, transit trucks, construction equipment, etc.). When inhaled, CO enters the bloodstream and reduces the body’s ability to deliver oxygen to vital organs and tissues. At extremely high concentrations, CO can result in death.

More information can be found at

Sulfur Dioxide (SO2)

Mecklenburg County is currently in compliance with National Ambient Air Quality Standard for sulfur dioxide (SO2).

SO2 is one of a group of highly reactive gases known as "oxides of sulfur." It is produced from the burning of fossil fuels that contain sulfur (coal and oil) by locomotives, large ships, and non-road equipment and the smelting of mineral ores (aluminum, copper, zinc, lead and iron).

SO2 can adversely affect:

  • public health as a respiratory irritant;

  • the environment by damaging crops and forming acid rain; and

  • visibility through the presence of suspended sulfate particulates in the atmosphere.

More information can be found at

Nitrogen Dioxide (NO2)

Mecklenburg County is currently in compliance with National Ambient Air Quality Standard for nitrogen dioxide (NO2).

NO2 is a highly reactive gas that forms quickly from emissions from combustion sources (e.g. cars, trucks and buses, power plants, and off-road equipment). In addition to contributing to the formation of ground-level ozone and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.
NO2 levels have remained steady in Mecklenburg County and are not likely to exceed the healthy levels. New control strategies for limiting ozone formation will likely involve reducing nitrogen dioxide emissions from both industrial and mobile sources.

More information can be found at

Lead (Pb)

Mecklenburg County is in compliance with National Ambient Air Quality Standard for lead (Pb).

Lead is a metal found naturally in the environment as well as in manufactured products. The major source of lead emissions had historically been from fuels in on-road motor vehicles (such as cars and trucks) until lead was prohibited from gasoline in 1996. Now, the highest levels of lead concentrations are usually found near lead smelters. Other stationary sources that produce lead emissions are waste incinerators, utilities and lead-acid battery manufacturers. Mecklenburg County does not have any large lead sources and monitored concentrations of lead have been well below the NAAQS, approximately 2% of the NAAQS.  On April 30, 2016, lead monitoring in Mecklenburg was discontinued as allowed by federal requirements. 

Health effects resulting from lead exposure are neurological effects in children and cardiovascular effects (e.g., high blood pressure and heart disease) in adults. Infants and young children are especially sensitive to even low concentrations of lead.

More information can be found at