Ozone (/ˈzn/), or trioxygen, is an inorganic molecule with the chemical formula O
. It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O
, breaking down in the lower atmosphere to O
(dioxygen). Ozone is formed from dioxygen by the action of ultraviolet (UV) light and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the latter, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.

Ball and stick model of ozone
Spacefill model of ozone
IUPAC name
Systematic IUPAC name
Other names
4-trioxidiene; catena-trioxygen
3D model (JSmol)
ECHA InfoCard 100.030.051
EC Number
  • 233–069–2
MeSH Ozone
RTECS number
  • RS8225000
  • InChI=1S/O3/c1-3-2 Y
  • InChI=1/O3/c1-3-2
  • [O-][O+]=O
Molar mass 47.997 g·mol−1
Appearance Colourless to pale blue gas[1]
Odor Pungent[1]
Density 2.144 mg cm−3 (at 0 °C)
Melting point −192.2 °C; −313.9 °F; 81.0 K
Boiling point −112 °C; −170 °F; 161 K
1.05 g L−1 (at 0 °C)
Solubility in other solvents Very soluble in CCl4, sulfuric acid
Vapor pressure 55.7 atm[2] (−12.15 °C or 10.13 °F or 261.00 K)[lower-alpha 1]
+6.7·10−6 cm3/mol
1.2226 (liquid), 1.00052 (gas, STP, 546 nm—note high dispersion)[3]
Hybridisation sp2 for O1
0.53 D
238.92 J K−1 mol−1
142.67 kJ mol−1
GHS labelling:
H270, H314
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
12.6 ppm (mouse, 3 hr)
50 ppm (human, 30 min)
36 ppm (rabbit, 3 hr)
21 ppm (mouse, 3 hr)
21.8 ppm (rat, 3 hr)
24.8 ppm (guinea pig, 3 hr)
4.8 ppm (rat, 4 hr)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 0.1 ppm (0.2 mg/m3)[1]
REL (Recommended)
C 0.1 ppm (0.2 mg/m3)[1]
IDLH (Immediate danger)
5 ppm[1]
Related compounds
Related compounds
Sulfur dioxide
Disulfur monoxide
Cyclic ozone
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)

Ozone's odour is reminiscent of chlorine, and detectable by many people at concentrations of as little as 0.1 ppm in air. Ozone's O3 structure was determined in 1865. The molecule was later proven to have a bent structure and to be weakly diamagnetic. In standard conditions, ozone is a pale blue gas that condenses at cryogenic temperatures to a dark blue liquid and finally a violet-black solid. Ozone's instability with regard to more common dioxygen is such that both concentrated gas and liquid ozone may decompose explosively at elevated temperatures, physical shock or fast warming to the boiling point.[5] It is therefore used commercially only in low concentrations.

Ozone is a powerful oxidant (far more so than dioxygen) and has many industrial and consumer applications related to oxidation. This same high oxidizing potential, however, causes ozone to damage mucous and respiratory tissues in animals, and also tissues in plants, above concentrations of about 0.1 ppm. While this makes ozone a potent respiratory hazard and pollutant near ground level, a higher concentration in the ozone layer (from two to eight ppm) is beneficial, preventing damaging UV light from reaching the Earth's surface.

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This article uses material from the Wikipedia article Ozone, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.