Shop Windows to the Universe

Warnings: The True Story of How Science Tamed the Weather by Mike Smith tells the story of our storm warning system. See our online store book collection.
This is a drawing of the structure of the molecule naphthalene, a PAH.
Click on image for full size
JPL/NASA

PAH

PAH is the short name for a "polycyclic aromatic hydrocarbon". A PAH is a stable structure made up of multiple rings that are fused together. The rings are made of carbon and hydrogen (though other elements sometimes sneak into the structure!).

These rings are tough to break apart. They are held together by a type of hybrid bond (hybrid between a single and double bond) that is actually stronger than the single or double bond with which you might be familiar.

Many people think that all aromatic molecules contain one or more benzene rings. This is a historical misconception. Benzene rings are found in many, but not all aromatic molecules. Many of the plants that were first found to contain benzene rings, such as vanilla or sassafras, were smelly...aromatic! So, it is a common misconception that all aromatic molecules contain benzene rings...when in fact, some do not (they contain other forms of carbon and hydrogen).

PAHs form easily. PAHs are very abundant in the solar system as well as in space. The red color in many interstellar clouds, such as this one comes from radiation in red wavelengths of PAH chemicals in the clouds. PAHs are found in comets and in meteorites, even ones which come from Mars. This was especially important when scientists thought there might be fossils of ancient life in a Martian rock.

One of the chief sources of terrestrial PAHs today is automobile emissions. PAH is also relatively abundant in burnt meat. When the body tries to break down the PAHs in burnt (or barbecued meat), the intermediates can be carcinogenic.

Shop Windows to the Universe Science Store!

Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, ranging from seismology, rocks and minerals, oceanography, and Earth system science to astronomy!

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

Element (Chemical Element)

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more

The possible discovery of Life on Mars

In July, 1996, it was announced that Dr. David McKay, along with a team of scientists at Johnson Space Center (a division of NASA), had discovered possible fossils of bacteria in an ancient rock from Mars....more

Looking for Life's garbage

Most forms of life leave evidence behind that they are there. Plants use up carbon dioxide and release oxygen. Some bacteria are known to release nitrogen into the environment. People leave behind smog,...more

Nitric Acid - HNO3

Nitric acid is a colorless, corrosive liquid and a toxic acid which can cause severe burns. Nitric acid consists of nitrogen, oxygen, and hydrogen atoms. Nitric acid, in its gas phase, is present in very...more

Sulfuric Acid - H2SO4

Sulfuric acid is a viscous, oily liquid and a strong acid which can cause severe burns. Sulfuric acid consists of sulfur, oxygen, and hydrogen atoms. Sulfuric acid is one of the components of acid rain....more

Methane - CH4

Methane is gas that is found in small quantities in Earth's atmosphere. Methane is the simplest hydrocarbon, consisting of one carbon atom and four hydrogen atoms. Methane is a powerful greenhouse gas....more

Ammonia - NH3

Ammonia is a chemical compound that is a colorless, flammable gas at normal temperatures and pressures. Ammonia is toxic, corrosive to some materials, and has a pungent odor. An ammonia molecule (NH3)...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