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Propane is an example of a hydrocarbon. Here are four different ways chemists use to show a molecule of propane. In the colored molecule models, carbon is light gray and hydrogen is white.
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Windows to the Universe original artwork by Randy Russell.


There is a group of chemicals called hydrocarbons. The molecules of hydrocarbons are made of hydrogen and carbon atoms.

Most kinds of fuel have hydrocarbons in them. Hydrocarbons store energy. Coal, oil, and natural gas all have hydrocarbons in them.

When we burn fuels with hydrocarbons, we make carbon dioxide (CO2) gas. The carbon dioxide goes into the air. Sometimes the burning makes carbon monoxide (CO), too.

Some hydrocarbons help make air pollution. Some of them are part of chemicals called Volatile Organic Compounds (VOCs). VOCs are some of the chemicals in smog.

Here are some of the hydrocarbons that you may have heard of: methane (CH4), butane (C4H10), propane (C3H8), benzene (C6H6), ethane (C2H6), and hexane (C6H14).

Last modified February 15, 2006 by Randy Russell.

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Most things around us are made of groups of atoms bonded together into packages called molecules. The atoms in a molecule are held together because they share or exchange electrons. Molecules are made...more

Air Pollution Sources

Air pollution comes from many different sources. Natural processes that affect air quality include volcanoes, which produce sulfur, chlorine, and ash particulates. Wildfires produce smoke and carbon monoxide....more

Carbon Dioxide - CO2

Carbon dioxide (CO2) is a kind of gas. There isn't that much carbon dioxide in Earth's atmosphere, but it is still very important. Carbon dioxide is a greenhouse gas. That means it helps trap heat coming...more

Carbon Monoxide - CO

Carbon monoxide is kind of gas. It is poisonous. A molecule of carbon monoxide (CO) has one carbon atom and one oxygen atom. Earth's atmosphere has a small amount of carbon monoxide in it. The carbon monoxide...more

Air Pollution

What do smog, acid rain, carbon monoxide, fossil fuel exhausts, and tropospheric ozone have in common? They are all examples of air pollution. Air pollution is not new. As far back as the 13 th century,...more

Volatile Organic Chemicals (VOCs)

Volatile Organic Compounds or VOCs are organic chemicals that form a gas at room temperature. They are called organic because they contain the element carbon.. There are many types of VOCs. Hydrocarbons...more

Photochemical Smog

Smog is a type of air pollution. Smog is a mixture of smoke and fog. Smog usually forms when smoke from pollution mixes with fog. For example, London, England, is often very foggy. Most people in London...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA