Compound Information
What is it?
- Carbon Monoxide (CO), one of six U.S. EPA criteria air pollutants , is a colorless, non-irritating, odorless, and tasteless gas.
Where does it come from?
- CO is found in both indoor and outdoor air. It is made when carbon fuel is not burned completely and is produced from both human-made and natural sources. Sources inside a home may include unvented kerosene and gas space heaters, leaking chimneys and furnaces, gas stoves and tobacco smoke. Sources in the outdoor air include automobile exhaust or other machinery that burn fossil fuels.
Why measure it outdoors?
- High levels of CO may cause health effects in certain people. Public health officials monitor air quality of CO for many different reasons, including protecting against adverse health effects.
How might it affect my health?
- Breathing air with a high concentration of CO reduces the amount of oxygen that can be transported in the blood stream to critical organs like the heart and brain. At very high levels, which are possible indoors or in other enclosed environments, CO can cause dizziness, confusion, unconsciousness and death.
- Very high levels of CO are not likely to occur outdoors. However, when CO levels are elevated outdoors, they can be of particular concern for people with some types of heart disease. These people already have a reduced ability for getting oxygenated blood to their hearts in situations where the heart needs more oxygen than usual. They are especially vulnerable to the effects of CO when exercising or under increased stress. In these situations, short-term exposure to elevated CO may result in reduced oxygen to the heart accompanied by chest pain also known as angina.
Where can I learn more?
The CDC has a carbon monoxide “ToxFAQs” fact sheet and additional information can be seen on EPA’s site here.
Potential Sources of Carbon Monoxide
What is it?
- Volatile Organic Compounds (VOCs) are a class of carbon-containing chemicals, such as alcohols, that easily evaporate into the air. Most scents/odors result from VOCs.
Where does it come from?
- VOCs are released during wildfires, and man-made sources include fossil fuel combustion, motor vehicle exhaust, various industrial processes, and solvent usage. At home, VOCs may be emitted from printers and copiers, from building materials such as carpet and linoleum, and from a variety of consumer products including paints, cleaning products, cigarettes, adhesives, arts and craft supplies, candles, air fresheners, and pesticides. At refineries, the common sources of VOCs are associated with the production of fuels, storage tanks, pipelines, and waste areas.
Why measure it?
- Some VOCs are major contributors to smog and include a variety of chemicals, some of which may have short- and long-term adverse health effects. Changes in VOCs may indicate a change in air quality that can be looked at further.
How might it affect my health?
- Every VOC is different in the types of health effects that it may cause. Some VOCs do not cause any adverse health effects while other VOCs can cause cancer. The health effects of short-term exposure to various VOCs may include eye, nose, and throat irritation; headaches; dizziness; and vision or memory problems. Long-term exposure to VOCs may include nausea, fatigue, loss of coordination, or damage to the liver, kidneys, or central nervous system.
Where can I learn more?
The EPA has information on VOCs .
Potential Sources of VOCs
What is it?
- Benzene is a colorless to light-yellow liquid at room temperature with a characteristic sweet odor. It is highly flammable and readily evaporates due to its high volatility. Once released into the air, benzene can be inhaled and absorbed into the body, where it has the potential to interfere with normal cellular functions and may adversely affect blood cells.
Where does it come from?
- Benzene is found in emissions from burning coal and oil, motor vehicle exhaust, evaporation from gasoline service stations, and industrial solvents. It is also found in naturally-occurring sources, such as volcanic eruptions and forest fires, and it is contained in cigarette smoke. Benzene is widely used in the production of rubbers, dyes, detergents, explosives, pharmaceuticals, and pesticides. It is also used as a component in motor fuels and as a solvent for fats, waxes, resins, oils, inks, paints, plastics, and rubber, and to extract oils from seeds and nuts.
Why measure it outdoors?
- As a volatile organic compound (VOC), benzene can contribute to the formation of ground-level ozone and smog and can cause various acute (short-term) or chronic (long-term) health effects if concentrations are high enough. Public health officials monitor air quality of benzene for several different reasons, including protecting against adverse health effects.
How might it affect my health?
- Benzene can adversely affect the body by disrupting normal cellular processes and impairing cell function. The severity of benzene-related health effects depends on several factors, including the magnitude, route, and duration of exposure, as well as the individual's characteristics such as age and medical conditions. Acute (short-term) inhalation exposure to high levels of benzene may cause irritation of the skin, eyes, and upper respiratory tract, as well as drowsiness, dizziness, and headaches, while inhalation exposure to very high levels can cause unconsciousness; dermal exposures can lead to redness and blisters. Chronic (long-term) inhalation of certain levels of benzene has been linked to blood disorders and has been shown to cause both structural and numerical chromosomal abnormalities in humans. Benzene specifically affects bone marrow (the tissue responsible for producing blood cells). Chronic benzene exposure may cause aplastic anemia (a risk factor for acute non-lymphocytic leukemia), particularly in occupational settings, as well as excessive bleeding and immune system damage, including altered antibody levels and decreased white blood cells. The USEPA and the International Agency for Research on Cancer (IARC) have classified benzene as a known human carcinogen for all routes of exposure.
Where can I learn more?
The CDC provides a benzene "ToxFAQs" fact sheet, and additional information is available on the EPA's website here.
Potential Sources of Benzene
What is it?
- Toluene is a clear, colorless liquid at room temperature with a distinct odor similar to paint thinner. It is highly flammable and readily evaporates due to its high volatility, and it does not usually stay in the environment for a long period. In surface water or soil, it will readily evaporate into the air or be degraded by bacteria. The central nervous system is the primary target organ for toluene toxicity in both humans and animals during acute (short-term) and chronic (long-term) exposures.
Where does it come from?
- Toluene is found in naturally-occurring sources like crude oil and the tolu tree. It can be found in common household products like paints, paint thinners, adhesives, synthetic fragrances, and nail polish, and it is also present in cigarette smoke. Toluene is widely used in the synthesis of organic chemicals, like benzene, and in the production of polymers, solvents, paints, coatings, synthetic fragrances, adhesives, inks, dyes, cosmetic nail products, and cleaning agents.
Why measure it outdoors?
- As a volatile organic compound (VOC), toluene contributes to the formation of ground-level ozone and smog and can cause various acute (short-term) or chronic (long-term) health effects if concentrations are high enough. Public health officials monitor air quality of toluene for several different reasons, including protecting against adverse health effects.
How might it affect my health?
- Toluene can adversely affect the body by disrupting normal cellular processes and impairing cell function. The severity of toluene-related health effects depends on several factors, including the magnitude, route, and duration of exposure, as well as the individual's characteristics such as age and medical conditions. Acute (short-term) exposure to low to moderate levels of toluene can irritate the nose, throat, eyes, and lungs, and may cause headaches, dizziness, tiredness, confusion, weakness, drunken-type actions, memory loss, and nausea; these symptoms usually disappear when exposure stops. Cardiac arrhythmia has also been reported in humans acutely exposed to toluene. Chronic (long-term) daily inhalation exposure to toluene may affect the nervous system, liver, and kidneys, and may cause hearing and color vision loss. Exposure to high levels of toluene during pregnancy, such as those associated with solvent abuse, may lead to developmental effects, such as reduced mental abilities and growth in children. The USEPA has concluded that currently there is inadequate information to assess the carcinogenic potential of toluene.
Where can I learn more?
The CDC provides a toluene "ToxFAQs" fact sheet, and additional information is available on the EPA's website here.
Potential Sources of Toluene
What is it?
- Ethylbenzene is a colorless, flammable liquid at room temperature with a characteristic gasoline-like odor. It is highly flammable and readily evaporates due to its high volatility, easily evaporating into the air from water and soil. Exposure to high levels of ethylbenzene can cause dizziness, as well as throat and eye irritation.
Where does it come from?
- Ethylbenzene occurs naturally in coal tar and petroleum, and is present in manufactured products such as inks, pesticides, and paints. It is primarily used to produce styrene, a key component in plastics. Other applications include its use as a solvent, in fuels, and in the production of various chemicals.
Why measure it outdoors?
- As a volatile organic compound (VOC), ethylbenzene contributes to air pollution, especially in urban and industrial areas, and plays a role in the formation of ground-level ozone and smog. Ethylbenzene can cause various acute (short-term) or chronic (long-term) health effects if concentrations are high enough, so monitoring ethylbenzene levels in the community can be important for public health.
How might it affect my health?
- Ethylbenzene can adversely affect the body by disrupting normal cellular processes and impairing cell function. The severity of ethylbenzene-related health effects depends on several factors, including the magnitude, route, and duration of exposure, as well as the individual's characteristics such as age and medical conditions. Acute (short-term) inhalation exposure to high levels of ethylbenzene may cause headaches, dizziness, and respiratory, eye, nose, and throat irritation. Chronic (long-term) exposure, even at lower levels, may lead to neurological effects, hearing loss, or kidney damage (as evidenced in animals). The International Agency for Research on Cancer (IARC) has classified ethylbenzene as a possible human carcinogen.
Where can I learn more?
The CDC provides an ethylbenzene "ToxFAQs" fact sheet, and additional information is available on the EPA's website here.
Potential Sources of Ethylbenzene
What is it?
- Xylenes are colorless, sweet-smelling liquids at room temperature that are highly flammable. Xylene evaporates quickly from soil and surface water into the air. There are three forms of xylene in which the methyl groups vary on the benzene ring: meta-xylene, ortho-xylene, and para-xylene (m-, o-, and p-xylene). These different forms are referred to as isomers.
Where does it come from?
- Outdoor emissions of xylenes typically originate from various industrial, commercial, and transportation sources, such as fuels, automobile exhaust, and evaporative emissions. Xylenes occur naturally in petroleum and crude oil, coal tar, and forest fires. Xylenes are primarily used to produce styrene (a key component in plastics), in the production of various chemicals, and as a solvent in the printing, rubber, and leather industries.
Why measure it outdoors?
- As a group of volatile organic compounds (VOCs), xylenes contribute to air pollution and are involved in the formation of ground-level ozone and smog. Monitoring outdoor xylenes helps assess air quality and identify pollution sources. Xylenes can cause various acute (short-term) or chronic (long-term) health effects if concentrations are high enough, so monitoring xylene levels in the community can be important for public health.
How might it affect my health?
- The severity of xylenes-related health effects depends on several factors, including the magnitude, route, and duration of exposure, as well as the individual's characteristics such as age and medical conditions. Acute (short-term) inhalation exposure to xylenes at high enough concentrations could result in irritation of the eyes, nose, and throat, gastrointestinal effects, and neurological effects. Chronic (long-term) inhalation exposure of humans to xylenes results primarily in central nervous system effects, such as headache, dizziness, fatigue, tremors, and incoordination; respiratory, cardiovascular, and kidney effects have also been reported. The International Agency for Research on Cancer (IARC) has classified xylenes as 'not classifiable as to its carcinogenicity to humans' due to inadequate evidence in humans and experimental animals.
Where can I learn more?
The CDC provides a xylenes "ToxFAQs" fact sheet, and additional information is available on the EPA's website here.
Potential Sources of Xylenes
What is it?
- Hydrogen sulfide is a colorless, flammable gas with a rotten egg odor. It can be smelled at very low concentrations in air, at least 1,000 times below the level that would cause eye and lung irritation.
Where does it come from?
- There are natural and man-made sources of hydrogen sulfide. Natural sources of hydrogen sulfide include emissions from geothermal fields, volcanic gases, and the breakdown of animal and plant wastes. Because of the latter, hydrogen sulfide is present in emissions from swamps, sewers, sewage treatment facilities and landfills. Hydrogen sulfide occurs naturally in crude oil and natural gas depending on the level of sulfur in the source. Crude oil with a low concentration of sulfur is often referred to as “sweet crude,” and oil with a higher level of sulfur is known as “sour crude.” Common sources of hydrogen sulfide emissions at refineries are associated with the transfer, storage, and processing of crude oil and the combustion of natural gas.
Why measure it?
- Because hydrogen sulfide can be smelled at such low levels, its measurement can help identify potential leaks in order to address community odor concerns.
How might it affect my health?
- Hydrogen sulfide at high levels can cause watery eyes and/or induce symptoms related to the loss of sense of smell, including headache, nausea, or vomiting. At extremely high levels, hydrogen sulfide can be deadly, particularly in enclosed spaces—the gas is heavier than air and interferes with our ability to breathe oxygen.
Where can I learn more?
CDC has a hydrogen sulfide “ToxFAQs” fact sheet.
Potential Sources of Hydrogen Sulfide
What is it?
- Sulfur dioxide (SO2), one of six U.S. EPA criteria air pollutants , is a colorless gas with a burnt match smell.
Where does it come from?
- Sulfur dioxide is emitted naturally (e.g. volcanoes) and by man-made sources including burning coal and other sulfur-containing fuels. At home, sulfur dioxide comes from natural gas stoves, fireplaces, lawnmowers, barbecues, hot water heaters, and other appliances. At refineries, sulfur dioxide is generated from fuel-fired furnaces and boilers, fluid catalytic cracking units, and sulfur recovery units and flares.
Why measure it?
- Sulfur dioxide and its reaction products contribute to smog formation. Public health officials monitor air quality of SO2 for many different reasons, including protecting against adverse health effects.
How might it affect my health?
- At high levels, sulfur dioxide can irritate the lungs, cause difficulty breathing, and cause burning of the nose or throat. Children, the elderly, and people, with asthma, heart disease, or chronic lung disease (such as bronchitis or emphysema) are most susceptible.
Where can I learn more?
The CDC has a sulfur dioxide “ToxFAQs” fact sheet.
Potential Sources of Sulfur Dioxide
What is it?
- Nitrogen oxides (NOx), Nitrogen dioxide (NO2) and Nitrogen oxide (NO) or NOx, are a group of gases composed of nitrogen and oxygen in varying amounts. NO2, one of six U.S. EPA criteria air pollutants , is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. NO2 is used as the indicator for the larger group of nitrogen oxides.
Where does it come from?
- The most common source of nitrogen oxides is motor vehicle exhaust. These compounds also form from wood burning, welding, kerosene heaters, gas stoves and tobacco smoke. At refineries, a common source of NOx is the fluid catalytic cracking unit.
Why measure it?
- Nitrogen oxides are major contributors to smog. NOx combines with volatile organic compounds (VOCs) in the atmosphere and reacts with sunlight to form ozone and particulate matter. Public health officials monitor air quality of NOx for many different reasons, including protecting against adverse health effects.
How might it affect my health?
- Low levels of nitrogen oxides can irritate the eyes, nose, throat, and lungs, and may cause a cough, shortness of breath, tiredness, and nausea. Exposure to higher levels of NOx can damage the respiratory airways. NO2 exposure also can intensify allergic responses in asthmatics.
Where can I learn more?
The EPA has information on nitrogen dioxide. In addition, the CDC has a nitrogen oxides “ToxFAQs” fact sheet.
Potential Sources of Nitrogen Oxides
What is it?
- Particulate matter, or PM2.5, is very small particles in air that are 2.5 micrometers (about 1 ten-thousandth of an inch) or less in diameter. This is less than the thickness of a human hair. Particulate matter, one of six U.S. EPA criteria air pollutants , is a mixture that can include organic chemicals, dust, soot and metals.
Where does it come from?
- These particles can come from cars and trucks, factories, wood burning, and other activities.
Why measure it?
- Particulate matter contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems.
How might it affect my health?
- Exposure to such particles can affect both your lungs and your heart. Particle pollution exposure has been linked to a variety of problems, including:
- premature death in people with heart or lung disease
- nonfatal heart attacks
- irregular heartbeat
- aggravated asthma
- decreased lung function
- increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing
Where can I learn more?
The EPA has information on Particulate Matter (PM) Basics. In addition, the CDC has information on PM.
Potential Sources of Particulate Matter
About Acute Exposure Guideline Levels (AEGLs)
https://www.epa.gov/aegl/about-acute-exposure-guideline-levels-aegls
Access Acute Exposure Guideline Levels (AEGLs) Values
https://www.epa.gov/aegl/access-acute-exposure-guideline-levels-aegls-values#chemicals
Technical Assistance Document for the Reporting of Daily Air Quality — the Air Quality Index (AQI)
https://www.airnow.gov/sites/default/files/2020-05/aqi-technical-assistance-document-sept2018.pdf
EPA’s Particulate Matter (PM) Pollution Basics
https://www.epa.gov/pm-pollution/particulate-matter-pm-basics