Pollution from automobile engines is a major source of ingredients for photochemical 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, hence the name (SMoke + fOG = SMOG). Victorian-era London was famous for its thick smogs, which resulted from the city's frequent, naturally occurring, heavy fogs that combined with smoke from coal fires which were used to heat homes.

Photochemical smog was first described in the 1950s. Photochemical smog is a mixture of air pollutants which have been chemically altered into further noxious compounds by exposure to sunlight.

The main components of photochemical smog are nitrogen oxides, Volatile Organic Compounds (VOCs), tropospheric ozone, and PAN (peroxyacytyl nitrate). All of these substances are very chemically reactive and are irritating to humans and other living things. They tend to smell bad, degrade materials, cause respiratory problems and illnesses, and irritate the eyes and other mucous membranes.

Some of the compounds in photochemical smog form when energy from sunlight transforms various pollutants into other unpleasant substances. For example, PAN forms when VOCs that have been altered into other chemicals by photodissociation combine with nitrogen dioxide.

Smog is obviously a major problem in many large urban areas, especially those with a lot of automobile traffic. Some of the constituents of smog can also be carried by the winds far from where they were formed, inflicting rural regions with the pollutants from large cities.

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:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

PAN (Peroxyacytyl nitrate) - C2H3O5N

PAN (Peroxyacytyl nitrate) is a toxic chemical that is an important component of smog. PAN is a gas at normal temperatures and pressures. Its chemical formula is C2H3O5N. PAN molecules are composed of...more

Photodissociation

Sometimes when a photon hits a molecule, the energy from the photon causes the molecule to break apart. Scientists use the term "photodissociation" for such events. Photodissociation plays a very important...more

Atmospheric Chemistry of Earth's Troposphere

Chemistry plays an influential role in the behavior of the lowest layer of Earth's atmosphere, the troposphere. The various gases in the troposphere are constantly mixing with and reacting with each other....more

Nitrogen

Nitrogen is a chemical element with an atomic number of 7 (it has seven protons in its nucleus). Molecular nitrogen (N2) is a very common chemical compound in which two nitrogen atoms are tightly bound...more

Hydrocarbons

There is a large class of important chemical compounds whose molecules are made up entirely of carbon and hydrogen atoms. These compounds, as a group, are called "hydrocarbons". Hydrocarbons are the critical...more

Greetings from the Tecamac Technical University Site

It’s been two weeks since we arrived in Mexico and it’s been a real challenge to recreate our laboratory in a trailer in the field in this desert-like location – Tecamac – north of the Federal District...more

Hazy day at T1

Things are quite busy here at T1 and we are all anxiously awaiting the delivery of the 3 NCAR seacontainers. The past few days have been quite polluted as you can see from this photo from the roof of a...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