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.

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 .

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.

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.

What is it?

• Nitrogen oxides (NO_x), Nitrogen dioxide (NO₂) and Nitrogen oxide (NO) or NO_x, 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 (NO_x). 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 NO_x is the fluid catalytic cracking unit.

Why measure it?

• Nitrogen oxides are major contributors to smog. NO_x 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 NO_x 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 NO_x 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.

What is it?

• Particulate matter, or PM_2.5, 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.