Does ozone occur naturally at ground level and is it safe to breathe?
Asked by: Bill Bryan


Ozone or tri-oxygen (O3) is mostly prominent in the earths atmosphere (20-50 Km above the surface of the earth).

It is produced when oxygen molecules (O2) dissociate into their constituent atoms under the influence of UV-C radiation (below 240 nm) and then combine with O2 molecules to form ozone. Ozone can also be formed in the lower atmosphere from nitrogen oxides and other pollutants by photochemical reactions. The most common way to make ozone is to pass O2 molecules through an electrical discharge. Indeed, when using an electric drill the strong odour that can usually be detected is actually ozone.

In any significant quantities ozone is not safe to breathe as it is an exceptionally good oxidizing agent and will attack living cells and tissue within the human body.
Answered by: Kevin Parker, B.S., Chemistry Graduate, Midlands UK


Ozone is produced as a result of many factors, some are man-made, some originate from the nature. It is produced as a result of ionization of oxygen in the air. The most common nature factors are ultraviolet light and lightning bolts, while man-made are laser printers or photocopiers. Ozone is a toxic gas, blue in color, with sharp, pungent odour. In some countries, such as Germany, low concentrations of ozone are used in therapy as a potent disinfection agent. Others, such as USA disallow such practices.

As an interesting fact of trivia: ozone is produced in your body by the white blood cells, which allows them to fight infection more effectively.
Answered by: Alexander Shapiro, Computer Science Undergrad Student, TAU, Tel-Aviv


Ozone occurs very rarely at ground level, and usually it is due to lightning. Free oxygen in the atmosphere is even more rare, and because of the electrons, oxygen rapidly combines with other elements. The most common state of oxygen is O2, which is 2 oxygen molecules sharing the orbits of a few of their outer electrons. However, in certain instances, especially when very high energies are applied, the O2 molecule picks up a third oxygen, becoming O3 - ozone. Ozone is an unstable molecule and over time will decompose into O2 and a free Oxygen. The layer of ozone in the upper atmosphere is continually disintegrating and being replenished. Ozone is not specifically toxic, but is dangerous to breathe, it causes or contributes to asthma and breathing difficulties. The main cause or contributor to low-level ozone is air pollution from automobiles and gas stations. In a temperature inversion, auto exhaust and free vaporized gasoline sit under sunlight and the resultant stew of chemicals produces a number of nasty things that also include ozone. Ozone is a main component of smog. So - for the short answers: Lightning produces ozone naturally at ground level, cars + gas stations contribute heavily to man-made ozone, and ozone is harmful to your health but will not kill you outright.
Answered by: Frank DiBonaventuro, B.S., Air Force Officer, Physics grad, The Citadel


Ozone can occur at ground level. It is one product of "smog". It is produced in small amounts by lightning discharges. It is also produced by 254 nm ultraviolet radiation from "germicidal" mercury lamps as a photochemical reaction product with oxygen. It is a powerful oxidizing agent, which is extremely toxic. The IDLH (Immediate Danger to Life and Health) concentration of ozone is only 5 ppm, 6 times the intrinsic toxicity of hydrogen fluoride at 30 ppm! The 8 hr. time weighted average [TWA] concentration limit for exposure to O3 set by OSHA is 0.1 ppm, compared to 3 ppm for HF, or 1/30 the permissible TWA concentration of HF.
Answered by: Vince Calder, Ph.D., physical chemist (retired)

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