Ozone
[CAS# 10028-15-6]

Identification

• Classification: Inorganic chemical industry >> Industrial gases such as hydrogen, nitrogen and oxygen
• Name: Ozone
• Synonyms: Triatomic oxygen
• Molecular Formula: O₃
• Molecular Weight: 48.00
• CAS Registry Number: 10028-15-6
• EC Number: 233-069-2
• SMILES: [O-][O+]=O

Properties

• Density: 1.46 g/cm^3*
• Melting point: 193 ºC^**
• Boiling point: -110 ºC^***

^* McLennan, J. C.; Philosophical Magazine (1798-1977) 1927, V3, P383-9.

^** Brown, Callaway; Journal of Chemical Physics 1954, V22, P1151-2.

^*** Riesenfeld, E. H.; Naturwissenschaften 1922, V10, P470-1.

Safety Data

• Hazard Symbols: GHS03;GHS05;GHS06;GHS07;GHS08;GHS09 Danger
• Hazard Statements: H270-H314-H315-H318-H319-H330-H335-H341-H372-H373-H400-H410
• Precautionary Statements: P203-P220-P244-P260-P261-P264-P264+P265-P270-P271-P273-P280-P284-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P351+P338-P305+P354+P338-P316-P317-P318-P319-P320-P321-P332+P317-P337+P317-P362+P364-P363-P370+P376-P391-P403-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Oxidising gases	Ox. Gas	1	H270
Acute toxicity	Acute Tox.	1	H330
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Eye irritation	Eye Irrit.	2	H319
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Serious eye damage	Eye Dam.	1	H318
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Skin corrosion	Skin Corr.	1B	H314
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Germ cell mutagenicity	Muta.	2	H341
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Acute toxicity	Acute Tox.	2	H330

Discovory and Applicatios

Ozone is an allotrope of oxygen with the molecular formula O₃. It consists of three oxygen atoms arranged in a bent molecular geometry and is distinguished from diatomic oxygen by its greater oxidizing power and characteristic sharp odor. Ozone was first recognized in 1840 by Christian Friedrich Schönbein, who observed a distinct smell during electrical discharges in air and named the substance from the Greek word meaning “to smell.” Subsequent experimental work established that the gas was a triatomic form of oxygen produced when molecular oxygen is subjected to electrical sparks or ultraviolet radiation.

During the latter half of the 19th century, chemists clarified the composition and reactivity of ozone through systematic laboratory studies. It was shown that ozone decomposes to ordinary oxygen and that it reacts readily with a wide range of organic and inorganic substances. Spectroscopic and analytical measurements confirmed its molecular formula and demonstrated that it absorbs ultraviolet radiation strongly. By the early 20th century, its bent structure and bonding characteristics had been determined using physical methods, including spectroscopy and later microwave and diffraction techniques.

A major scientific milestone in the understanding of ozone came with the recognition of its presence in the upper atmosphere. Observations in the late 19th and early 20th centuries revealed that a layer of ozone exists in the stratosphere. This ozone layer plays a crucial role in absorbing a significant fraction of incoming solar ultraviolet radiation, particularly in the UV-B range. The mechanism of ozone formation and destruction in the stratosphere was described in the 1930s by Sidney Chapman, who proposed a set of photochemical reactions in which molecular oxygen is dissociated by ultraviolet light, forming atomic oxygen that subsequently combines with O₂ to generate O₃. These reactions, along with catalytic cycles involving trace species, account for the dynamic equilibrium that maintains the ozone layer.

The discovery of stratospheric ozone and its protective function established ozone as a substance of planetary importance. Later atmospheric research demonstrated that certain anthropogenic compounds can catalytically destroy ozone, leading to measurable depletion in polar regions. International scientific assessments confirmed the chemical processes responsible for ozone depletion and provided the basis for coordinated environmental policy responses.

At ground level, ozone is also formed by photochemical reactions involving nitrogen oxides and volatile organic compounds in the presence of sunlight. This tropospheric ozone is a component of photochemical smog and has been extensively studied because of its effects on human health, vegetation, and materials. Controlled exposure experiments and field measurements have documented that elevated ozone concentrations can irritate respiratory tissues and impair lung function.

In addition to its atmospheric roles, ozone has been developed for practical applications based on its strong oxidizing properties. Industrial ozone generation is typically achieved by passing dry air or oxygen through an electrical discharge, producing ozone in situ. One of its earliest large-scale applications was in water treatment. Beginning in the late 19th century, ozone was used in municipal water purification systems to inactivate microorganisms and to oxidize organic and inorganic contaminants. Its effectiveness against bacteria and viruses has been demonstrated in numerous controlled studies, and ozone treatment is now employed in drinking water facilities and wastewater processing plants in various countries.

Ozone is also used in air purification and odor control, where it oxidizes odorous compounds. In the chemical industry, it participates in ozonolysis reactions, a process in which ozone cleaves carbon-carbon double bonds in alkenes to form carbonyl compounds. This reaction has become a standard method in organic synthesis for structural analysis and for the preparation of aldehydes, ketones, and carboxylic acids. The reaction mechanism, involving the formation of molozonide and ozonide intermediates, has been elucidated through kinetic and spectroscopic investigations.

The discovery of ozone in electrical experiments, the elucidation of its molecular structure, and the recognition of its atmospheric and chemical significance illustrate the progressive integration of laboratory chemistry and environmental science. Today, ozone remains central to studies of atmospheric chemistry, public health, water treatment, and synthetic methodology, reflecting a well-established body of experimental evidence regarding its properties and applications.

References

2025. Physical activity modifies the association between ambient air pollution and comorbid depression and disability in activities of daily living. Scientific Reports.
DOI: 10.1038/s41598-025-09341-z

2025. Ozone pollution induced-yield loss of major staple crops in China and effects from COVID-19. Journal of Environmental Sciences (China).
DOI: 10.1016/j.jes.2025.02.034