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Ozone

DESIGNATIONS

CAS No.: 10028-15-6
Registry name: Ozone
Chemical name: Ozone
Synonyms, Trade names: Trioxygen
Chemical name (German): Ozon
Chemical name (French): Ozone
Appearance: colourless gas or dark blue liquid (at -112C)

BASIC CHEMICAL AND PHYSICAL DATA

Empirical formula: O3
Rel. molecular mass: 48.0 g
Density: 2.15 g/l (gaseous) at 0C and 1013 hPa, 1.571 g/cm3 at -183C (liquid)
Relative gas density: 1.66
Boiling point: -112C
Melting point: -192.7C
Vapour pressure: 7 x 106 Pa at -20C
Flash point:  
Ignition temperature:  
Explosion limits:  
Odour threshold: 0.01-0.02 ppm
Solvolysis/solubility: in water 490 ml/l at 25C; highly soluble in Freon 12
Conversion factors: 1 mg/m3 = 0.51 ppm
1 ppm = 1.995 mg/m3

ORIGIN AND USE

Usage:
Used in laboratories for ozonisation; in industry for bleaching oils, greases, waxes, synthetic fibres, papers, cellulose and textiles; as disinfectant in breweries, cold stores and the like; for artificial ageing of brandy and disinfection of drinking water. It is also used for sterilising swimming-pool water and for the deodourisation of unpleasant smells. Further applications result from the sterilising effect of ozone in the manufacture, preservation and storage of foodstuffs.

Origin/derivation:
Ozone is produced from atmospheric oxygen in the presence of UV light at extremely high temperatures and e.g. in an electrical corona discharge. Its formation under natural conditions presupposes the existence of appropriate precursors (in particular N-oxides and hydrocarbons) which are converted to ozone in the presence of sufficient sunlight. The main sources of workplace impact are inert-gas welding, photocopiers, air filtration systems, UV sterilisation systems and UV lamps where ozone is produced in the respiratory zone from molecular oxygen through UV irradiation. The only economical method of producing ozone is that of electrical corona discharge.

Toxicity

Humans: LD 15-20 ppm acc. ULLMANN, 1978
0.001 mg/l air (definite irritation) acc. TAB. Chemie, 1980
0.002 mg/l air (1.5 h; damage) acc. TAB. Chemie, 1980
Mammals:
Guinea pigs LC50 51.7 ppm acc. ULLMANN, 1978
Mouse LC50 21 ppm acc. ULLMANN, 1978

Note:
Young animals react more sensitively to the inhalation of ozone than older ones. Physical exercise increases the toxicity level due to increased ventilation or stress.

Characteristic effects:

Humans/mammals: Ozone is extremely irritating to the mucous membranes of the eyes, nose and throat. The main damage is however caused in the respiratory tract and this manifests itself in a reduced respiratory volume or even in bronchitis and pulmonary oedemas. Chronic exposure may lead to chest pain, headache and dizziness even if the ozone concentration is low. The toxicity of ozone is attributed in part to the oxidative decomposition of unsaturated fatty acids in the organism.

Plants: The direct effect of ozone is the destruction of chlorophyll and in particular chlorophyll b. The extent to which ozone is involved in the phenomenon of "dying forests" has been the subject of discussion for some time. Ozone absorption takes place exclusively via the atmosphere. There is a considerable difference in the sensitivity of various plants. Acute symptoms of ozone damage are necrosis, chlorosis and so-called water marks.

ENVIRONMENTAL BEHAVIOUR

Water:
The rate at which ozone decomposes in an aqueous solution increases with increasing pH. In the presence of water, ozone oxidises all metals to the maximum possible extent.

Air:
Atmospheric air pollution caused by ozone originates from the photochemical formation of smog. The first step in this process is the photolysis of ozone.

Degradation, decomposition products, half-life:
Gaseous ozone is subject to spontaneous decomposition: O3 (r) O2 + 1/2 O2 + 284 kJ with a half-life of 3 days (at 20C), 8 days (at -15C), 18 days (at -25C) or 3 months (at -50C); the decomposition process does however only involve simple allotropic conversion of the same element.

ENVIRONMENTAL STANDARDS

Medium/acceptor Sector Country/organ. Status Value Cat. Remarks Source
Air:   CH

(L)

100 g/m3

  1) acc. LAU-BW, 1989
  CH

(L)

120 g/m3

  2) acc. LAU-BW, 1989
  D

G

120 g/m3

  3) acc. LAU-BW, 1989
  WHO

G

150-200 g/m3

  4) acc. LAU-BW, 1989
  WHO

G

100-120 g/m3

  5) acc. LAU-BW, 1989
  WHO

G

200 g/m3

  6) acc. LAU-BW, 1989
  WHO

G

60 g/m3

  7) acc. LAU-BW, 1989
  WHO

G

65 g/m3

  8) acc. LAU-BW, 1989
Workp D

L

0.2 mg/m3

MAK   DFG, 1989
Workp DDR

(L)

0.2 mg/m3

    acc. Tab. Chemie, 1980
Workp SU

(L)

0.1 mg/m3

    acc. KETTNER, 1979
Workp USA

(L)

0.2 mg/m3

TWA   acc. ACGIH, 1986
Workp USA

(L)

0.6 mg/m3

STEL   acc. ACGIH, 1986

Notes:

1) Exposure time: 98% of annual half-hour average
2) Exposure time: 1 hour average; may be exceeded once
3) Exposure time: half-hour average; protection of humans
4) Exposure time: 1 h; protection of humans
5) Exposure time: 8 h; protection of humans
6) Exposure time: 1 h; protection of vegetation
7) Exposure time: mean value over entire vegetation period
8) Exposure time: 24 h; protection of vegetation

Assessment/comments

Any assessment of ozone must give consideration to two different aspects. Ozone which pollutes the air just above the ground harms the respiratory organs and plants and thus should be avoided as far as possible. In view of the secondary formation of ozone, this means reducing above all the nitrous emission levels.

At the same time, chlorinated fluorocarbons and nitrous oxides must not be allowed to reach the upper strata of the atmosphere (ozonosphere at an altitude of 50 - 60 km), since such substances deplete the vitally important ozone layer which absorbs dangerous UV radiation. While ozone concentrations close to the ground have a harmful effect, their presence in the upper atmosphere is absolutely vital.


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