Pollutant Descriptions

Ozone • PM2.5 • Carbon Monoxide • Nitrogen Dioxide • Sulfur Dioxide • Lead
The six pollutants listed below are considered "criteria" pollutants and have National Ambient Air Quality Standards (NAAQS) set by the EPA Office of Air Quality Planning and Standards (OAQPS).

Ozone (O3)

Description: A colorless gas that is a major constituent of smog. This pollutant alone contributes to the majority of unhealthy air quality days in CT, as measured by the Air Quality Index (AQI). Ozone is found both at high altitude and ground level. High altitude ozone is beneficial because it shields the earth from the sun's ultraviolet radiation. Ground level ozone is harmful because it reacts with the mucus membranes of the respiratory system and causes inflammation.
Sources: Forms in the air from other pollutants: volatile organic compounds (VOCs) and nitrogen oxides (NO and NO2) in the presence of ultraviolet (UV) radiation. Ozone does not come directly from any source. The VOCs that form ozone come from vehicle and industrial exhaust as well as evaporation of gasoline, solvents and paints, and many other sources.
Health Impacts: Irritates the lungs and breathing passages, causing coughing and pain in the chest and throat. Increases susceptibility to respiratory infections and reduces the ability to exercise. Effects are more severe in children, the elderly and people with asthma and other respiratory ailments. Long-term exposure may lead to scarring of lung tissue and reduced lung efficiency.

Fine Particles (PM2.5)

Description: Solid matter or liquid droplets with an aerodynamic diameter of 2.5 microns or less.
Sources: Diesel cars, trucks and buses; power plants; industries and many other sources.
Health Impacts: Aggravates existing heart and lung diseases, changes the body's defenses against inhaled materials and damages lung tissue. Lung impairment can persist for 2-3 weeks after exposure to high levels of particulate matter. Chemicals in and on particulates can also be toxic. Very fine particulates can be inhaled deeply into the lungs. When PM2.5 reaches unhealthy levels, people with respiratory or heart disease, the elderly and children are most at risk. Particulate matter also damages paint, soils clothing and furniture, and reduces visibility.

Carbon Monoxide (CO)

Description: An odorless, colorless gas resulting from incomplete combustion of fossil fuel burning.
Sources: Product of the incomplete burning of carbon in fuels from automobiles, buses, trucks, small engines, boilers and some industrial processes. High concentrations can be found in confined spaces such as parking garages, poorly ventilated tunnels, or traffic intersections, especially during peak hours.
Health Impacts: Weakens the heart's contractions and lowers the amount of oxygen carried by the blood. Reduces one's ability to exercise and is dangerous for people with chronic heart disease. Causes nausea, dizziness, headaches, visual impairment, and under high concentrations, even death. 

Nitrogen Dioxide (NO2)

Description: A yellowish brown, highly reactive gas that is the primary ingredient in formation of ground-level ozone.
Sources: Formed from high temperature combustion such as in power plants and automobile engines.
Health Impacts: Short-term NO2 exposures, ranging from 30 minutes to 24 hours, can produce adverse respiratory effects including increased asthma symptoms, more difficulty controlling asthma, and an increase in respiratory illnesses and symptoms. Studies also show a connection between short-term exposure and increased visits to emergency roomd and hospital admissions for respiratory illnesses, particularly in at risk populations including children, the elderly, and asthmatics.

Sulfur Dioxide (SO2)

Description: A colorless gas, odorless at low concentrations but pungent at very high concentrations.
Sources: Sulfur dioxide is generated primarily by the burning of fuels that contain sulfur. The contributors to the release of sulfur dioxide in Connecticut are oil and coal fired power plants, industrial sources, residential heating and motor vehicles.
Health Impacts: Aggravates existing lung diseases, especially bronchitis. Constricts the breathing passages, especially in people with asthma and people doing moderate to heavy exercise. Causes wheezing, shortness of breath, and coughing. High levels of particulates appear to worsen the effect of sulfur dioxide, and long-term exposures to both pollutants leads to higher rates of respiratory illness. When sulfur dioxide reaches unhealthy levels, people with asthma are most at risk. It is also the main contributor to acid rain and particulate pollution.


Description: Lead is a dull gray, odorless, tasteless heavy metal.
Sources: The presence of lead in the atmosphere is primarily accounted for by man-made processes such as the extraction and processing of metallic ores, the incineration of solid waste and fuel combustion. The most important sources of lead in humans and other animals come from ingestion of foods and beverages, inhalation of airborne lead and the eating of non-food substances such as lead-containing paint chips.
Health Impacts: Clinical lead poisoning is accompanied by symptoms of intestinal cramps, peripheral nerve paralyses, anemia, and severe fatigue. High levels of exposure results in permanent neurological, renal, or cardiovascular damage or death. May cause damage to the brain and other parts of the body's nervous system. Children are most susceptible to the effects of lead. Lead can also harm wildlife.
Content last updated on December 20, 2010