What Is Ozone? Definition and Facts

What Is Ozone
Ozone or trioxygen is an oxygen molecule that contains three oxygen atoms. In the upper atmosphere, it protects against UV radiation. But, it is a pollutant near the surface.

Ozone is an inorganic oxygen molecule with the chemical formula O3. It is a reactive allotrope of oxygen that also goes by the name trioxygen. Ozone protects the planet from harmful ultraviolet radiation, yet is also acts as a pollutant near the Earth’s surface and carries health risks. The compound has many uses, including disinfection and cleaning, plus it is an important chemical precursor. Here are ozone facts, including its history, what it smells like, its health effects, and its uses.


In 1785, Dutch chemist Martinus van Marum noticed a strange smell from generating electrical sparks above water. While van Marum realized the odor came from a chemical reaction, he did not understand its source.

German-Swiss chemist Christian Friedrich Schönbein repeated van Marum’s experiment and realized the odor was identical to the smell in the air after a lightning strike. In 1839, he successfully isolated the gas from air and named it “ozone.” The name comes from the Greek word ozein, which means to smell.”

The chemical formula for ozone was determined in 1865 by Jacques-Louis Soret.

What Does Ozone Smell Like?

Ozone has a pungent odor, similar to that of chlorine. You smell it in the air after lightning or a short in electrical equipment. It is sort of a dry, burning aroma.

In the second half of the 19th century and part of the 20th century, people associated the acrid odor of ozone with freshness and good health. This is somewhat surprising, since Schönbein reported having difficulty breathing, chest pain, and irritated mucous membranes from inhaling the compound. Scientists demonstrated exposure to ozone either killed small mammal or else left animals sluggish and gasping for breath.

Ozone Health Effects

Some people enjoy the scent of ozone, but it has both immediate and chronic health effects. People suffering from asthma, COPD, or lung cancer are more likely to be hospitalized after a thunderstorm. Ozone as air pollution increases a person’s risk of death, particularly from respiratory and cardiovascular causes. One study of 450,000 people in the United States showed a 30% increase in the risk of dying from lung disease for people living in cities with high ozone levels, such as Los Angeles and Houston.

Ozone irritates the eyes and mucous membranes and causes edema (swelling) in the lungs. Inhaled ozone reacts with compounds on the lung lining, forming cholesterol-based metabolites that contribute to atherosclerotic plaques in arteries.

However, the human body and other organisms also produce ozone. White blood cells use ozone to kill pathogens. Some plant roots, such as those of marigolds, release ozone to kill microbes and deter growth of other plants.

The OSHA permissible exposure limit for ozone is 0.1 μmol/mol over an 8-hour weighted average time. A concentration of 5 μmol/mol is classified as “Immediately Dangerous to Life and Health.”

What Is the Ozone Layer?

While ozone in the air near the ground is a pollutant, ozone in the stratosphere protects the surface from damaging ultraviolet radiation. The ozone layer is a region of the lower stratosphere, typically ranging from 15 to 35 kilometers (9 to 22 miles) above the Earth’s surface. In this layer, ozone concentration ranges from around 2 to 8 parts per million. The layer thickness varies geographically and also seasonally. Also, it is thickest in spring and thinnest in autumn. It is thickest near the equator and thinnest near the poles. This explains why the ozone hole caused by anthropogenic ozone depletion primarily affected Antarctica.

Ozone forms when ultraviolet light strikes normal oxygen molecules (O2) and splits them into oxygen atoms. Atomic oxygen then combines with O2 and forms O3.

Even though the ozone layer only contains a low concentration of the molecule, it is enough for absorbing harmful solar ultraviolet radiation. The combination of O2 and O3 entirely screens harmful UV-C and most UV-B. Some UV-B and nearly all UV-A reaches the Earth’s surface. Although this portion of ultraviolet light is less damaging than UV-C, it still causes premature skin aging, some genetic damage, cataracts, and skin cancer. However, the body also uses UV-B to make vitamin D.

Ozone Uses

Aside from its role in the immune system and function in the ozone layer, ozone serves many uses.

  • Ozone is a powerful disinfectant and bleach.
  • It deodorizes air and is popular for removing smoke and musty odors.
  • It kills bacteria, mold, and fungi on food.
  • Ozone disinfects drinking water and sanitizes water for pools an spas.
  • It is a useful in manufacturing a variety of chemicals, including pharmaceuticals and organic compounds.
  • Ozone improves ink adhesion onto plastic.
  • It detoxifies cyanide waste.

Air purifies that generate ozone generally pose a health risk. The levels of ozone necessary to sanitize air and surfaces exceed safe inhalation levels.

Interesting Ozone Facts

Here are some additional interesting ozone facts.

  • Ozone levels on aircraft are higher than levels found on the ground. Some planes use ozone converters as a means of reducing passenger and crew ozone exposure.
  • Like regular diatomic oxygen (O2), ozone gas is colorless to pale blue. Liquid ozone is deep blue. Solid ozone is violet.
  • Some other planets also have ozone layers. For example, Venus has a thin ozone layer around 100 kilometers above the surface.
  • Like O2, ozone is paramagnetic. In other words, it is weakly attracted to magnetic fields.