Criteria Air Pollutants and Their Negative Health Effects

Last updated on July 21, 2025

The EPA has identified six pollutants (called criteria air pollutants) that are the most common and have the most impact on human health, carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO₂), ozone (O₃), particulate pollution (PM2.5 and PM10), and sulfur dioxide (SO₂).

These pollutants are carefully measured using the National Ambient Air Quality Standards (NAAQS) and each state is required by law to keep the amounts of these pollutants under the allowed levels.

Access the federal standards here, and the nonattainment status of each Pennsylvania county here (as you can see from this table, Philadelphia County has been meeting the federal standards for PM2.5 since 2014).

Each of these pollutants is severely harmful to human health and being exposed for long periods of time may do irreversible damage to lung, heart, and organ health. Below is a table of the criteria air pollutants, their sources, known health effects, and environmental effects.

Criteria Air Pollutant	Sources	Known Health Effects
Carbon monoxide (CO)	Incomplete fuel combustion from cars or industry	At high levels it can stop oxygen from reaching the heart and brain which could cause dizziness, confusion, unconsciousness, and death. This level can only occur indoors or in enclosed spaces.
Lead (Pb)	Waste incineration, electric utilities, lead batteries.	Prolonged exposure effects the nervous system, kidney function, immune system, reproductive and developmental systems, and the cardiovascular system.
Nitrogen Dioxide (NO2)	Fuel combustion	Short exposure can lead to respiratory irritation, while long term exposure can worsen existing respiratory conditions or contribute to developing respiratory conditions.
Ozone (O3)	Formed when UV radiation comes into contact with other pollutants.	At ground level, ozone can cause throat irritation, reduced lung function, and harm lung tissue. Additionally, it may aggravate preexisting lung conditions, such as asthma, bronchitis, or emphysema, causing severe health issues.
Particulate Matter (PM2.5, PM10)	Fuel combustion, dust, fires, industrial processes	Exposure can impact both the lungs and the heart. At any level of exposure, this can increase risk of heart attack or asthma attack, decrease lung function, and may cause premature death.
Sulfur Dioxide (SO2)	Industrial fuel combustion, refineries	Harms respiratory function long term and may make breathing difficult.

Many of these pollutants also have significant effects on the environment. Decreased plant growth, caused by harming the plant’s respiratory system, has been a noted symptom of high levels of criteria air pollutants. Additionally, Ozone is a greenhouse gas, negatively affecting our climate, by warming the earth.

You can do your part in keeping levels of these pollutants low by driving less, not burning waste, and, most importantly, keeping polluting industries accountable for their actions.

One project done by the Clean Air Task Force, Death by Diesel, explores the health outcomes of diesel fuel exhaust, PM2.5 exhaust known as diesel particulate matter (DPM). Explore their map of the US here.