Pollution from cars is one of the main causes of smog.
Click on image for full size
UCAR

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 used to heat their homes by burning coal. The coal made lots of smoke, which mixed with fog to form smog. London used to have a lot of smog.

There is a special kind of smog called photochemical smog. It forms when photons of sunlight hit molecules of different kinds of pollutants in the atmosphere. The photons make chemical reactions happen. The pollution molecules turn into other kinds of nasty chemicals. That mixture of bad chemicals is called photochemical smog.

The chemicals in photochemical smog include nitrogen oxides, Volatile Organic Compounds (VOCs), ozone, and PAN (peroxyacytyl nitrate). Nitrogen oxides mostly come from the engines of cars and trucks. VOCs are given off by paint, gasoline, and pesticides. Ozone is a form of oxygen that is harmful. PAN is a type of pollution that is made by chemical reactions between other kinds of pollution.

Smog smells bad and makes it hard for people to breath. It can also damage materials. Smog is a very harmful kind of air pollution.

Last modified February 21, 2006 by Randy Russell.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

The Earth Scientist, Volume XXV, Issue 3, Fall 2009

The Fall 2009 issue of The Earth Scientist includes a collection of Earth and Space Science articles for you, covering the current efforts to save Louisiana’s Lake Pontchartrain, student research into building design as it relates to earthquake damage, an exciting Earth Science project and resource from the United Kingdom...more

Photodissociation

Photons are tiny bits of light and other kinds of electromagnetic radiation. Photons can sometimes break apart molecules. When this happens, it is called photodissociation. When a photon runs into a molecule,...more

Molecules

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

PAN (Peroxyacytyl nitrate) - C2H3O5N

PAN (Peroxyacytyl nitrate) is a kind of air pollution. It is part of smog. PAN makes people's eyes hurt and it is bad for your lungs. It also damages plants. PAN forms when some other kinds of chemicals...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

Atmospheric Chemistry of Earth's Troposphere

When you think of chemistry, do you think about mixing colored liquids in test tubes and maybe making an explosion... or at least a nice puff of smoke? Did you know that a lot of chemistry happens in Earth's...more

Nitrogen

There is more nitrogen gas in the air than any other kind of gas. About 4/5ths of Earth's atmosphere is nitrogen gas! A molecule of nitrogen gas is made up of two nitrogen atoms. There are other molecules...more

Hydrocarbons

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,...more

Shop Windows to the Universe

This eudialyte pendant and earrings are available in our online store, along with other jewelry, minerals, fossils, classroom materials, and household items.

Generous sponsorship of Windows to the Universe is provided by the Hewlett Foundation, the American Geological Institute, the American Geophysical Union, the National Science Foundation, NASA, NCAR, and the CISM and CMMAP projects. NASA CMMAP AGU CISM NCAR Hewlett AGI NSF