Criteria pollutants, as defined by environmental agencies, are a group of common air pollutants that have known detrimental effects on human health and the environment.

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These pollutants are regulated by air quality standards to protect public health and the environment. The criteria pollutants were established by the United States Environmental Protection Agency (EPA) and are commonly used as a reference by many countries. The criteria pollutants include:

Ozone (O₃):

Source: Ozone is a secondary pollutant formed in the atmosphere through complex photochemical reactions involving precursor pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs).
Health Effects: Ground-level ozone can cause respiratory issues, aggravate asthma, and contribute to other respiratory problems.

Particulate Matter (PM10 and PM2.5):

Source: PM10 (particles with a diameter of 10 micrometers or smaller) and PM2.5 (particles with a diameter of 2.5 micrometers or smaller) are emitted directly from sources such as vehicles, construction sites, and industrial activities. They can also form in the atmosphere through complex reactions.
Health Effects: Inhalation of particulate matter can lead to respiratory and cardiovascular problems. Fine particles (PM2.5) are especially concerning as they can penetrate deep into the lungs and even enter the bloodstream.

Nitrogen Dioxide (NO₂):

Source: NO₂ is primarily emitted from combustion processes, such as those in vehicles and power plants.
Health Effects: NO₂ irritates the respiratory system and can contribute to respiratory issues. It also plays a role in the formation of ground-level ozone and particulate matter.

Sulfur Dioxide (SO₂):

Source: SO₂ is produced by burning fossil fuels containing sulfur, such as coal and oil, in power plants and industrial facilities.
Health Effects: SO₂ can irritate the respiratory system, leading to breathing difficulties. It also contributes to the formation of fine particulate matter.

Carbon Monoxide (CO):

Source: CO is produced by incomplete combustion of carbon-containing fuels, such as gasoline and wood.
Health Effects: High levels of carbon monoxide can be lethal as it interferes with the body’s ability to transport oxygen. Lower levels can lead to headaches, dizziness, and fatigue.

Lead (Pb):

Source: Historically, lead was added to gasoline, but regulations have significantly reduced this source. Other sources include industrial activities, lead-based paint, and lead-acid batteries.
Health Effects: Lead exposure can lead to neurological and developmental issues, especially in children. It can also cause kidney and cardiovascular problems in adults.

These criteria pollutants serve as indicators of air quality, and regulatory standards are set to limit their concentrations in the ambient air to protect public health and the environment. Monitoring and controlling these pollutants help mitigate adverse effects on air quality and the well-being of communities.