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EC number: 233-069-2
CAS number: 10028-15-6
Ozone is emitted to the outside atmosphere
locally in only very small quantities as detailed in the environmental
exposure assessment. This locally emitted ozone will, after dispersion,
not influence the level of ozone already (naturally) present at
ground-level, and will be subject to the same removal processes as the
‘natural’ ozone. Annual average background ozone levels (natural ozone)
in the northern hemisphere range between approximately 40–90 µg/m³
(20–45 ppb), depending on location, elevation and level of anthropogenic
influence (Vingarzan, 2004). In some areas and at some points in time
the concentration of ground level ozone can be considerably higher.
Since emission of industrially produced
ozone constitutes only a negligible contribution to the overall level of
atmospheric ozone, and since the latter has been well studied, most data
available refer to knowledge and studies in the context of atmospheric
ozone that is naturally present. One exception is the chamber study by
McClurkin et al. (2013) which tested the stability of ozone in air
within the context of disinfection of storage containers. The half-life
of ozone as a function of air movement, temperature and humidity was
determined. Half-life in still air at 24 °C and zero humidity was as
high as 1524 min (25.4 h). As airflow, temperature and humidity
increased, half-life decreased to 39 min. The self-decomposition of
ozone in indoor air (in the absence of pollutants and light) is
therefore strongly influenced by relative humidity, temperature and air
Ozone in air can be decomposed via complex
radical chain reactions in the presence of sunlight
(phototransformation). The phototransformation of ozone in ambient air
is well studied, and humidity was found to play an important role (also
see above). Ozone phototransformation is mainly accomplished by
radical-type chain reactions. Direct photolysis of ozone is much less
important (Jans and Hoigne, 2000).
Especially under dry conditions, ozone is
much more stable in air than in water. The half-life of ozone in ambient
air as measured by the US EPA is in the order of 12 hours (Rice and
The half-life of ozone in water is much
shorter compared to half-life values in air. Overall half-lives of ozone
in water were reported to range between 8 and 80 minutes (see IUCLID
section 5.6 for details).
The half-life of ozone decomposition in
sandy soil was approximately 40 minutes (Choi et al., 2002).
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