Ozone (
O3) is a
triatomic
molecule, consisting of three
oxygen atoms. It is an
allotrope of oxygen that is much less
stable than the
diatomic O
2.
Ground-level ozone is an
air pollutant
with harmful effects on the respiratory systems of animals. The
ozone layer in the upper
atmosphere filters potentially damaging
ultraviolet light from reaching the
Earth's surface. It is present in low
concentrations throughout the
Earth's
atmosphere. It has many industrial and consumer
applications.
Ozone, the first
allotrope of a
chemical element to be recognized by
science, was proposed as a distinct
chemical compound by
Christian Friedrich
Schönbein in 1840, who named it after the
Greek verb ozein (ὄζειν, "to smell"), from
the peculiar odor in
lightning storms. The
formula for ozone, O
3, was not determined until 1865 by
Jacques-Louis Soret and
confirmed by Schönbein in 1867.
Physical properties
Ozone is a pale blue gas, slightly soluble in water and much more
soluble in inert non-polar solvents such as
carbon tetrachloride or fluorocarbons,
where it forms a blue solution. At -112 °C, it condenses to
form a dark blue
liquid. It is dangerous to
allow this liquid to warm to its boiling point, because both
concentrated gaseous ozone and liquid ozone can detonate. At
temperatures below -193 °C, it forms a violet-black
solid.
Most people can detect about 0.01
ppm of ozone in air where it has a very
specific sharp odor somewhat resembling chlorine bleach. Exposure
of 0.1 to 1 ppm produces headaches, burning eyes, and irritation to
the respiratory passages.Even low concentrations of ozone in air
are very destructive to organic materials such as latex, plastics,
and lungs.
Ozone is
diamagnetic, meaning that it
will resist formation of a
magnetic
field and will decrease the energy stored in the field once the
field is established.
Structure
The structure of ozone, according to experimental evidence from
microwave spectroscopy, is
bent, with C
2v symmetry (similar to the
water molecule), O – O distance of 127.2 pm and O
– O – O angle of 116.78°. The central atom forms an
sp²
hybridization with one lone pair. Ozone is a polar molecule with a
dipole moment of 0.5337
D. The bonding can be expressed as a resonance hybrid
with a
single bond on one side and
double bond on the other producing an
overall
bond order of 1.5 for each
side.
Chemistry
Ozone is a powerful
oxidizing agent, far
better than dioxygen. It is also unstable at high concentrations,
decaying to ordinary diatomic oxygen (in about half an hour in
atmospheric conditions):
- 2 O3 → 3 O2
This reaction proceeds more rapidly with increasing temperature and
decreasing pressure.
Deflagration of
ozone can be triggered by a spark, and can occur in ozone
concentrations of 10 wt% or higher.
Metals
Ozone will oxidize
metals (except
gold,
platinum, and
iridium) to
oxides of the
metals in their highest
oxidation
state. For example:
- 2 Cu+ (aq) + 2 H3O+ (aq) +
O3 (g) → 2 Cu2+ (aq) + 3 H2O (l) +
O2 (g)
Non-metals
Ozone also increases the oxidation number of oxides, such as the
oxidation of
nitric oxide to
nitrogen dioxide:
- NO + O3 → NO2 + O2
This reaction is accompanied by
chemiluminescence. The NO
2 can
be further oxidized:
- NO2 + O3 → NO3 +
O2
The NO
3 formed can react with NO
2 to form
N2O5:
- NO2 + NO3 →
N2O5
Ozone reacts with
carbon to form
carbon dioxide, even at room
temperature:
- C + 2 O3 → CO2 + 2 O2
Ozone does not react with ammonium
salts but it
reacts with
ammonia to form
ammonium nitrate:
- 2 NH3 + 4 O3 →
NH4NO3 + 4 O2 +
H2O
Ozone reacts with
sulfides to make
sulfates. For example,
lead sulfide is oxidised to
lead sulfate:
- PbS + 4 O3 → PbSO4 + 4 O2
Sulfuric acid can be produced from
ozone, starting either from elemental
sulfur
or from
sulfur dioxide:
- S + H2O + O3 →
H2SO4
- 3 SO2 + 3 H2O + O3 → 3
H2SO4
All three
atoms of ozone may also react, as in
the reaction of
tin chloride with
hydrochloric acid and NaCl:
- 3 SnCl2 + 6 HCl + O3 → 3 SnCl4
+ 3 H2O
In the
gas phase, ozone reacts with
hydrogen sulfide to form sulfur
dioxide:
- H2S + O3 → SO2 +
H2O
In an
aqueous solution, however, two
competing simultaneous reactions occur, one to produce elemental
sulfur, and one to produce
sulfuric
acid:
- H2S + O3 → S + O2 +
H2O
- 3 H2S + 4 O3 → 3
H2SO4
Iodine perchlorate can be made by treating
iodine dissolved in cold
anhydrous perchloric
acid with ozone:
- I2 + 6 HClO4 + O3 → 2
I(ClO4)3 + 3 H2O
Solid
nitryl perchlorate can be made from
NO
2, ClO
2, and O
3 gases:
- 2 NO2 + 2 ClO2 + 2 O3 → 2
NO2ClO4 + O2
Combustion
Ozone can be used for
combustion
reactions and combusting gases; ozone provides higher temperatures
than combusting in
dioxygen
(O
2). The following is a reaction for the combustion of
carbon subnitride which can also
cause lower temperatures:
- 3 C4N2 + 4 O3 → 12 CO + 3
N2
Ozone can react at cryogenic temperatures. At 77 K (-196 °C),
atomic
hydrogen reacts with liquid ozone to
form a hydrogen
superoxide radical, which dimerizes:
- H + O3 → HO2 + O
- 2 HO2 → H2O4
Ozonides
Ozonides can be formed, which contain the
ozonide anion, O
3−. These
compounds are explosive and must be stored at cryogenic
temperatures. Ozonides for all the
alkali
metals are known. KO
3, RbO
3, and
CsO
3 can be prepared from their respective
superoxides:
- KO2 + O3 → KO3 +
O2
Although KO
3 can be formed as above, it can also be
formed from
potassium hydroxide
and ozone:
- 2 KOH + 5 O3 → 2 KO3 + 5 O2 +
H2O
NaO
3 and LiO
3 must be prepared by action of
CsO
3 in liquid NH
3 on an
ion exchange resin containing
Na
+ or Li
+ ions:
- CsO3 + Na+ → Cs+ +
NaO3
Treatment with ozone of
calcium dissolved in
ammonia leads to ammonium ozonide and not calcium ozonide:
- 3 Ca + 10 NH3 + 6 O3 → Ca·6NH3
+ Ca(OH)2 + Ca(NO3)2 + 2
NH4O3 + 2 O2 + H2
Applications
Ozone can be used to remove
manganese from
water, forming a
precipitate which can be filtered:
- 2 Mn2+ + 2 O3 + 4 H2O → 2
MnO(OH)2 (s) + 2 O2 + 4 H+
Ozone will also turn
cyanides to the one
thousand times less toxic
cyanates:
- CN- + O3 → + O2
Finally, ozone will also completely decompose
urea:
- (NH2)2CO + O3 → N2
+ CO2 + 2 H2O
Ozone in Earth's atmosphere

The distribution of atmospheric ozone
in partial pressure as a function of altitude.

Total ozone concentration in June 2000
as measured by EP-TOMS satellite instrument.
The standard way to express total ozone levels (the amount of ozone
in a vertical column) in the atmosphere is by using
Dobson units. Concentrations at a point are
measured in
parts per billion
(ppb) or in μg/m³.
Ozone layer
The highest levels of ozone in the atmosphere are in the
stratosphere, in a region also known as the
ozone layer between about 10 km and
50 km above the surface (or between about 6 and 31 miles).
Here it filters out
photons with shorter
wavelengths (less than 320 nm) of ultraviolet light, also
called UV rays, (270 to 400 nm) from the
Sun that would be harmful to most forms of
life in large doses. These same wavelengths are also
among those responsible for the production of
vitamin D, a vitamin also produced by the human
body. Ozone in the stratosphere is mostly produced from ultraviolet
rays reacting with oxygen:
- O2 + photon(radiation 240 nm)
→ 2 O
- O + O2 → O3
It is destroyed by the reaction with
atomic oxygen:
- O3 + O → 2 O2
The latter reaction is
catalysed by the
presence of certain free radicals, of which the most important are
hydroxyl (OH), nitric oxide (NO) and atomic chlorine (Cl) and
bromine (Br). In recent decades the amount of ozone in the
stratosphere has been declining mostly because of emissions of
CFC and
similar chlorinated and brominated organic molecules, which have
increased the concentration of ozone-depleting catalysts above the
natural background. Ozone only makes up 0.00006% of the
atmosphere.
Low level ozone
Low level ozone (or tropospheric ozone) is regarded as a pollutant
by the
World Health
OrganizationWHO-Europe reports:
Health
Aspects of Air Pollution (2003) (PDF) and the
United States
Environmental Protection Agency (EPA). It is not emitted
directly by
car engines
or by industrial operations, but formed by the reaction of sunlight
on air containing
hydrocarbon and
nitrogen oxides that react to form ozone
directly at the source of the pollution or many kilometers down
wind.
Ozone reacts directly with some hydrocarbons such as
aldehydes and thus begins their removal from the
air, but the products are themselves key components of
smog. Ozone
photolysis by UV light leads to production of the
hydroxyl radical OH and this plays
a part in the removal of hydrocarbons from the air, but is also the
first step in the creation of components of smog such as
peroxyacyl nitrates which can be
powerful eye irritants. The atmospheric lifetime of tropospheric
ozone is about 22 days; its main removal mechanisms are being
deposited to the ground, the above mentioned reaction giving OH,
and by reactions with OH and the peroxy radical HO
2·
(Stevenson et al., 2006).
There is evidence of significant reduction in agricultural yields
because of increased ground-level ozone and pollution which
interferes with
photosynthesis and
stunts overall growth of some plant species.
Certain
examples of cities with elevated ozone readings are Houston, Texas
, and Mexico City, Mexico
. Houston has a reading of around 41 ppb,
while Mexico City is far more hazardous, with a reading of about
125 ppb.
Ozone cracking
Ozone gas attacks any
polymer possessing
olefinic or
double bonds within its
chain structure, such materials including
natural rubber,
nitrile rubber, and
Styrene-butadiene rubber. Products made
using these polymers are especially susceptible to attack, which
causes cracks to grow longer and deeper with time, the rate of
crack growth depending on the load carried by the product and the
concentration of ozone in the atmosphere. Such materials can be
protected by adding
antiozonants, such
as waxes, which bond to the surface to create a protective film or
blend with the material and provide long term protection.
Ozone cracking used to be a serious problem
in car tires for example, but the problem is now seen only in very
old tires. On the other hand, many critical products like
gaskets and
O-rings may be
attacked by ozone produced within compressed air systems.
Fuel lines are often made from reinforced rubber
tubing and may also be susceptible to attack, especially within
engine compartments where low levels of ozone are produced from
electrical equipment. Storing rubber products in close proximity to
DC electric motors can accelerate the rate at
which ozone cracking occurs. The
commutator of the motor creates sparks
which in turn produce ozone.
Ozone as a greenhouse gas
Although ozone was present at ground level before the
Industrial Revolution, peak
concentrations are now far higher than the pre-industrial levels,
and even background concentrations well away from sources of
pollution are substantially higher. This increase in ozone is of
further concern because ozone present in the upper
troposphere acts as a
greenhouse gas, absorbing some of the
infrared energy emitted by the earth.
Quantifying the greenhouse gas potency of ozone is difficult
because it is not present in uniform concentrations across the
globe. However, the scientific review on the
climate change (the
IPCC Third Assessment Report) suggests
that the
radiative forcing of
tropospheric ozone is about 25% that of
carbon dioxide.
Health effects
Air pollution
There is a great deal of evidence to show that high concentrations
of ozone, created by high concentrations of pollution and daylight
UV rays at the Earth's surface, can harm lung function and irritate
the
respiratory system. A
connection has also been known to exist between increased ozone
caused by thunderstorms and hospital admissions of
asthma sufferers. Air quality guidelines such as
those from the World Health Organization are based on detailed
studies of what levels can cause measurable
health effects. Exposure to ozone and the
pollutants that produce it has been linked to premature death,
asthma,
bronchitis,
heart attack, and other cardiopulmonary
problems. According to scientists with the
United States
Environmental Protection Agency (EPA), susceptible people can
be adversely effected by ozone levels as low as 40 ppb.
The
Clean Air Act directs the EPA to
set
National
Ambient Air Quality Standards for several pollutants, including
ground-level ozone, and counties out of compliance with these
standards are required to take steps to reduce their levels. In May
2008, the EPA lowered its ozone standard from 80 ppb to 75 ppb.
This proved controversial, since the Agency's own scientists and
advisory board had recommended lowering the standard to 60 ppb, and
the
World Health
Organization recommends 51 ppb. Many public health and
environmental groups also supported the 60 ppb standard. On the
other hand, the EPA had already designated over 300 mostly urban
counties as out of compliance, and lowering the standard to 75 ppb
put hundreds more in non-compliance. Lowering it further to 60 ppb
would likely have left most of the US in non-compliance.
Manufacturers, employers, and others argued that the cost of
compliance with the lower standard would be prohibitive. The EPA
has also developed an Air Quality Index to help explain air
pollution levels to the general public. Eight-hour average ozone
concentrations of 85 to 104
ppb
are described as "Unhealthy for Sensitive Groups", 105 ppb to 124
ppb as "unhealthy" and 125 ppb to 404 ppb as "very
unhealthy".
Ozone can also be present in
indoor
air pollution, partly as a result of electronic equipment such
as photocopiers.
A common British folk myth dating back to the
Victorian era holds that the smell of the sea
is caused by ozone, and that this smell has "bracing" health
benefits. Neither of these is true. The characteristic "smell of
the sea" is not caused by ozone but by the presence of
dimethyl sulfide generated by
phytoplankton, and dimethyl sulfide, like
ozone, is toxic in high concentrations.
Long-term exposure to ozone has been shown to increase risk of
death from
respiratory illness.
A study of 450,000 people living in United States cities showed a
significant correlation between ozone levels and respiratory
illness over the 18-year follow-up period. The study revealed that
people living in cities with high ozone levels such as Houston or
Los Angeles had an over 30% increased risk of dying from lung
disease.
Physiology
Ozone, along with reactive forms of oxygen such as
superoxide,
singlet
oxygen,
hydrogen peroxide, and
hypochlorite ions, is naturally
produced by
white blood cells and
other biological systems (such as the roots of
marigolds) as a means of destroying foreign bodies.
Ozone reacts directly with organic double bonds. Also, when ozone
breaks down to dioxygen it gives rise to oxygen
free radicals, which are highly reactive and
capable of damaging many
organic
molecules. Ozone has been found to convert
cholesterol in the
blood
stream to plaque (which causes hardening and narrowing of
arteries). Moreover, it is believed that the powerful oxidizing
properties of ozone may be a contributing factor of
inflammation. The cause-and-effect relationship
of how the ozone is created in the body and what it does is still
under consideration and still subject to various interpretations,
since other body chemical processes can trigger some of the same
reactions. A team headed by Dr.
Paul Wentworth Jr. of the Department of Chemistry at
the
Scripps Research
Institute has shown evidence linking the antibody-catalyzed
water-oxidation pathway of the human
immune response to the production of ozone. In
this system, ozone is produced by antibody-catalyzed production of
trioxidane from water and
neutrophil-produced singlet oxygen.
When inhaled, ozone reacts with compounds lining the lungs to form
specific, cholesterol-derived metabolites that are thought to
facilitate the build-up and pathogenesis of
atherosclerotic plaques (a form of
heart disease). These metabolites have
been confirmed as naturally occurring in human atherosclerotic
arteries and are categorized into a class of secosterols termed
“Atheronals”, generated by
ozonolysis of
cholesterol's double bond to form a 5,6 secosterol as well as a
secondary condensation product via aldolization.
Ozone has been implicated to have an adverse effect on plant
growth, "...Ozone reduced total chlorophylls, carotenoid and
carbohydrate concentration, and increased
1-aminocyclopropane-1-carboxylic acid (ACC) content and ethylene
production. In treated plants, the ascorbate leaf pool was
decreased, while lipid peroxidation and solute leakage were
significantly higher than in ozone-free controls. The data
indicated that ozone triggered protective mechanisms against
oxidative stress in citrus."
Safety regulations
Due to the strongly oxidizing properties of ozone, ozone is a
primary irritant, affecting especially the eyes and respiratory
systems and can be hazardous at even low concentrations. The
Canadian Center for Occupation Safety and Health reports that:
"Even very low concentrations of ozone can be harmful
to the upper respiratory tract and the lungs.
The severity of injury depends on both by the
concentration of ozone and the duration of exposure.
Severe and permanent lung injury or death could result
from even a very short-term exposure to relatively low
concentrations."
To protect workers potentially exposed to ozone, OSHA has
established a permissible exposure limit (PEL) of 0.1 ppm (29 CFR
1910.1000 table Z-1), calculated as an 8 hour time weighted
average. Higher concentrations are especially hazardous and NIOSH
has established an Immediately Dangerous to Life and Health Limit
(IDLH) of 5 ppm. Work environments where ozone is used or where it
is likely to be produced should have adequate ventilation and it is
prudent to have a monitor for ozone that will alarm if the
concentration exceeds the OSHA PEL. Continuous monitors for ozone
are available from several suppliers.
Production
Ozone often forms in nature under conditions where O
2
will not react. Ozone used in industry is measured in g/nm³ or
weight percent. The regime of applied concentrations ranges from 1
to 5 weight percent in air and from 6 to 14 weight percent in
oxygen.
Corona discharge method
This is the most popular type of ozone generator for most
industrial and personal uses. While variations of the "hot spark"
coronal discharge method of ozone production exist, including
medical grade and industrial grade ozone generators, these units
usually work by means of a
corona
discharge tube. They are typically very cost-effective and do
not require an oxygen source other than the ambient air. However,
they also produce
nitrogen oxides as
a by-product. Use of an
air dryer can
reduce or eliminate nitric acid formation by removing water vapor
and increase ozone production. Use of an
oxygen concentrator can further increase
the ozone production and further reduce the risk of nitric acid
formation by removing not only the water vapor, but also the bulk
of the nitrogen.
Ultraviolet light
UV ozone generators employ a light source that generates a
narrow-band ultraviolet light, a subset of that produced by the
Sun. The Sun's UV sustains the ozone layer in the stratosphere of
Earth.While standard UV ozone generators tend to be less expensive,
they usually produce ozone with a concentration of about 0.5% or
lower. Another disadvantage of this method is that it requires the
air (oxygen) to be exposed to the UV source for a longer amount of
time, and any gas that is not exposed to the UV source will not be
treated. This makes UV generators impractical for use in situations
that deal with rapidly moving air or water streams (in-duct air
sterilization, for
example). Production of ozone is one of the
potential
dangers of
ultraviolet germicidal
irradiation.VUV Ozone generators are used in swimming pool and
spa applications ranging to millions of gallons of water. VUV Ozone
generators, unlike Corona Discharge generators) do not produce
harmful nitrogen by-products and also unlike Corona Discharge
systems, VUV Ozone generators work extremely well in humid air
environments. There is also not normally a need for expensive
off-gas mechanisms, and no need for air driers or oxygen
concentrators which require extra costs and maintenance.
Cold plasma
In the cold plasma method, pure oxygen gas is exposed to a
plasma created by
dielectric barrier discharge.
The diatomic oxygen is split into single atoms, which then
recombine in triplets to form ozone.
Cold plasma machines utilize pure oxygen as the input source and
produce a maximum concentration of about 5% ozone. They produce far
greater quantities of ozone in a given space of time compared to
ultraviolet production. However, because cold plasma ozone
generators are very expensive, they are found less frequently than
the previous two types.
The discharges manifest as filamentary transfer of electrons (micro
discharges) in a gap between two electrodes. In order to evenly
distribute the micro discharges, a dielectric
insulator must be used to separate the
metallic electrodes and to prevent arcing.
Some cold plasma units also have the capability of producing
short-lived allotropes of oxygen which include O
4,
O
5, O
6, O
7, etc. These anions are
even more reactive than ordinary O
3.
Special considerations
Ozone cannot be stored and transported like other industrial gases
(because it quickly decays into diatomic oxygen) and must therefore
be produced on site. Available ozone generators vary in the
arrangement and design of the high-voltage electrodes. At
production capacities higher than 20 kg per hour, a gas/water
tube heat-exchanger may be utilized as ground electrode and
assembled with tubular high-voltage electrodes on the gas-side. The
regime of typical gas pressures is around 2
bar absolute in oxygen and 3 bar absolute in air.
Several megawatts of
electrical power
may be installed in large facilities, applied as one phase AC
current at 50 to 8000 Hz and
peak
voltages between 3,000 and 20,000
volts. Applied voltage is usually inversely related to the applied
frequency.
The dominating parameter influencing ozone generation efficiency is
the gas temperature, which is controlled by cooling water
temperature and/or gas velocity. The cooler the water, the better
the ozone synthesis. The lower the gas velocity, the higher the
concentration (but the lower the net ozone produced). At typical
industrial conditions, almost 90% of the effective power is
dissipated as heat and needs to be removed by a sufficient cooling
water flow.
Because of the high reactivity of ozone, only few materials may be
used like
stainless steel (quality
316L),
titanium,
aluminium (as long as no moisture is present),
glass,
polytetrafluorethylene, or
polyvinylidene fluoride.
Viton may be used with the restriction of constant
mechanical forces and absence of humidity (humidity limitations
apply depending on the formulation).
Hypalon
may be used with the restriction that no water come in contact with
it, except for normal atmospheric levels.
Embrittlement or shrinkage is the common mode
of failure of elastomers with exposure to ozone. Ozone cracking is
the common mode of failure of elastomer seals like
O-rings.
Silicone rubbers are usually
adequate for use as
gaskets in ozone
concentrations below 1 wt%, such as in equipment for accelerated
ageing of rubber samples.
Incidental production
Ozone may be formed from O
2 by electrical discharges and
by action of high energy
electromagnetic radiation. Certain
electrical equipment generate
significant levels of ozone. This is especially true of devices
using
high voltages, such as
ionic air purifiers,
laser printers,
photocopiers,
tasers and
arc
welders.
Electric motors using
brush can generate ozone from
repeated
spark inside the unit. Large
motors that use brushes, such as those used by elevators or
hydraulic pumps, will generate more ozone than smaller
motors.
Ozone is similarly formed in the Catatumbo lightning storms phenomenon on
the Catatumbo River in Venezuela
, which helps to replenish ozone in the upper
troposhere. It is the world's
largest single natural generator of ozone, lending calls for it to
be designated a
UNESCO World
Heritage Site.
Laboratory production
In the laboratory, ozone can be produced by
electrolysis using a
9 volt battery, a pencil graphite rod
cathode, a
platinum
wire
anode and a 3
molar sulfuric acid electrolyte. The
half
cell reactions taking place are:
- 3 H2O → O3 + 6 H+ + 6
e− (ΔEo =
−1.53 V)
- 6 H+ + 6 e− → 3 H2
(ΔEo = 0 V)
- 2 H2O → O2 + 4 H+ + 4
e− (ΔEo = −1.23 V)
In the net reaction, three equivalents of water are converted into
one equivalent of ozone and three equivalents of
hydrogen. Oxygen formation is a competing
reaction.
It can also be prepared by passing 10,000-20,000 volts
DC through dry O
2. This can be
done with an apparatus consisting of two concentric glass tubes
sealed together at the top, with in and out spigots at the top and
bottom of the outer tube. The inner core should have a length of
metal foil inserted into it connected to one side of the power
source. The other side of the power source should be connected to
another piece of foil wrapped around the outer tube. Dry
O
2 should be run through the tube in one spigot. As the
O
2 is run through one spigot into the apparatus and
10,000-20,000
volts DC are applied to the foil leads,
electricity will discharge between the dry
dioxygen in the middle and form O
3 and O
2 out
the other spigot. The reaction can be summarized as follows:
- 3 O2 — electricity → 2 O3
Ionic air purifiers
Some air purifiers create ozone.
Applications
Industry
The largest use of ozone is in the preparation of
pharmaceuticals,
synthetic lubricants, as well as many
other commercially useful
organic
compounds, where it is used to sever
carbon-carbon bonds. It can also be used for
bleach substances and for killing
microorganisms in air and water sources. Many municipal drinking
water systems kill bacteria with ozone instead of the more common
chlorine. Ozone has a very high
oxidation potential. Ozone does not form
organochlorine compounds, nor does it
remain in the water after treatment. The Safe Drinking Water Act
mandate that these systems introduce an amount of chlorine to
maintain a minimum of 0.2 ppm residual Free Chlorine in the pipes,
based on results of regular testing. Where
electrical power is abundant, ozone is a
cost-effective method of treating water, since it is produced on
demand and does not require transportation and storage of hazardous
chemicals. Once it has decayed, it leaves no taste or odor in
drinking water.
Although low levels of ozone have been advertised to be of some
disinfectant use in residential homes, the concentration of ozone
in dry air required to have a rapid, substantial effect on airborne
pathogens exceeds safe levels recommended by the U.S.
Occupational
Safety and Health Administration and
Environmental
Protection Agency. Humidity control can vastly improve both the
killing power of the ozone and the rate at which it decays back to
oxygen (more humidity allows more effectiveness).
Spore forms of most pathogens are very tolerant of
atmospheric ozone in concentrations where asthma patients start to
have issues.
Industrially, ozone is used to:
- Disinfect laundry in hospitals, food factories, care homes
etc;
- Disinfect water in place of chlorine
- Deodorize air and objects, such as
after a fire. This process is extensively used in Fabric Restoration
- Kill bacteria on food or on contact surfaces;
- Sanitize swimming pools and spas
- Kill insects in stored grain
- Scrub yeast and mold spores from the air in food processing
plants;
- Wash fresh fruits and vegetables to kill yeast, mold and
bacteria;
- Chemically attack contaminants in water (iron, arsenic, hydrogen sulfide, nitrites, and complex organics lumped together as
"colour");
- Provide an aid to flocculation
(agglomeration of molecules, which aids in filtration, where the
iron and arsenic are removed);
- Manufacture chemical compounds via chemical synthesis
- Clean and bleach fabrics (the former use is utilized in Fabric
Restoration; the latter use is patented);
- Assist in processing plastics to allow adhesion of inks;
- Age rubber samples to determine the useful life of a batch of
rubber;
- Eradicate water borne parasites such as Giardia lamblia and Cryptosporidium in surface water
treatment plants.
Ozone is a
reagent in many
organic reactions in the laboratory and in
industry.
Ozonolysis is the cleavage of
an
alkene to
carbonyl
compounds.
Many hospitals in the U.S. and around the world use large ozone
generators to decontaminate operating rooms between surgeries. The
rooms are cleaned and then sealed airtight before being filled with
ozone which effectively kills or neutralizes all remaining
bacteria.
Ozone is used as an alternative to
chlorine
or
chlorine dioxide in the
bleaching of wood pulp . It is often
used in conjunction with oxygen and hydrogen peroxide to eliminate
the need for chlorine-containing compounds in the manufacture of
high-quality, white
paper
Ozone can be used to detoxify
cyanide wastes
(for example from
gold and
silver mining) by oxidizing
cyanide to
cyanate and eventually to
carbon dioxide.
Consumers
Devices generating high levels of ozone, some of which use
ionization, are used to sanitize and deodorize uninhabited
buildings, rooms, ductwork, woodsheds, and boats and other
vehicles.
In the U.S.,
air purifiers emitting
lower levels of ozone have been sold. This kind of air purifier is
sometimes claimed to imitate nature's way of purifying the air
without filters and to sanitize both it and household surfaces. The
United
States Environmental Protection Agency (EPA) has declared that
there is "evidence to show that at concentrations that do not
exceed public health standards, ozone is not effective at removing
many odor-causing chemicals" or "viruses, bacteria, mold, or other
biological pollutants." Furthermore, its report states that
"results of some controlled studies show that concentrations of
ozone considerably higher than these [human safety] standards are
possible even when a user follows the manufacturer’s operating
instructions." The government successfully sued one company in
1995, ordering it to stop repeating health claims without
supporting scientific studies.
Ozonated water is used to launder clothes and to sanitize food,
drinking water, and surfaces in the home. According to the
U.S. Food and Drug
Administration (FDA), it is "amending the
food additive regulations to provide for the
safe use of ozone in gaseous and aqueous phases as an
antimicrobial agent on food, including meat
and poultry." Studies at
California Polytechnic
University demonstrated that 0.3 ppm levels of ozone dissolved
in filtered tapwater can produce a reduction of more than 99.99% in
such food-borne microorganisms as salmonella, E. coli 0157:H7, and
Campylobacter. This quantity exceeds 20,000 times the WHO
recommended limits stated above.Ozone can be used to remove
pesticide residues from
fruits and
vegetables.
Ozone is used in homes and
hot tubs to kill
bacteria in the water and to reduce the amount of chlorine or
bromine required by reactivating them to their free state. Since
ozone does not remain in the water long enough, ozone by itself is
ineffective at preventing cross-contamination among bathers and
must be used in conjunction with these
halogens. Gaseous ozone created by ultraviolet
light or by corona discharge is injected into the water.
Ozone is also widely used in treatment of water in aquariums and
fish ponds. Its use can minimize bacterial growth, control
parasites, eliminate transmission of some diseases, and reduce or
eliminate "yellowing" of the water. Ozone must not come in contact
with fish's gill structures. Natural salt water (with life forms)
provides enough "instantaneous demand" that controlled amounts of
ozone activate bromide ion to
hypobromous acid, and the ozone entirely
decays in a few seconds to minutes. If oxygen fed ozone is used,
the water will be higher in dissolved oxygen, fish's gill
structures will atrophy and they will become dependent on higher
dissolved oxygen levels.
See also
References
Further reading
- Series in Plasma Physics: Non-Equilibrium Air Plasmas at
Atmospheric Pressure. Edited by K.H. Becker, U. Kogelschatz, K.H.
Schoenbach, R.J. Barker; Bristol and Philadelphia: Institute of
Physics Publishing Ltd; ISBN 0-7503-0962-8; 2005
External links