About O3

About O3

Ozone (O3) is a tri atomic form of oxygen, three oxygen atoms together to form one molecule.

Ozone Imagee

What is Ozone?

The oxygen atom is unstable in the atomic form. Oxygen is stable in the diatomic form as O2. The air we breathe today is made up of about 21% oxygen, this makes oxygen one of the most common molecules found in nature today.

Ozone is a triatomic form of oxygen, meaning that the molecule, ozone, is made up of 3 oxygen atoms. Unlike oxygen, ozone is a visible gas with a light blue color at very high concentrations. At low concentrations ozone is colorless. Ozone also has a distinct odor that is noticeable at very low levels and may be associated with a “clean” smell, at higher levels ozone has a very pungent odor. Ozone is an unstable gas that readily decomposes to oxygen naturally. Ozone is also a highly reactive gas that acts as a very strong chemical oxidant.


 Physical Properties of Oxygen and Ozone

Molecular FormulaO3O2
Molecular Weight48 g/mol32 g/mol
ColorLight blueColorless
SmellOdor threshold of 0.001 ppm, pungent at high levelsOdorless
Melting Point-192.5 deg C-218.79 deg C
Boiling point-111.9 deg C-1892.95 deg C
Critical Temperature-121 deg C-118.56 deg C
Critical Pressure54.5 atm5.043 atm
Density2.144 g/l @ 0 deg C1.429 g/l @ 0 deg C
Solubility @ 0 deg C0.64 g/100 ml0.049 g/100 ml
Electrochemical Potential2.07 V1.23 V

While ozone is the triatomic form of oxygen the differences in physical properties are vast.  While oxygen is not detectable by the human nose, ozone has an extremely low odor threshold.  Humans have the ability to detect ozone before many expensive measuring devices.  Also, ozone in air at high levels (greater than 0.1 ppm) is hazardous to human health.

The solubility of ozone is 13 times greater than oxygen.  While ozone still requires mechanical mixing devices to be dissolved into the water the ability to be dissolved into water is much greater than oxygen, and therefore lends ozone to be useful in many water treatment applications.

The electrochemical potential of ozone is much higher than oxygen which leads it to be one of the most powerful oxidants on earth.  This oxidation potential allows ozone to break down contaminates and kill bacteria faster than most every chemical alternative.

Chemical structure of ozone

Three molecules of oxygen will recombine to form two molecules of ozone. Two of an ozone molecule’s three atoms are bonded strongly, as in oxygen. The third atom is loosely bonded, making ozone gas 10 times more soluble in water than oxygen. Ozone has 24 protons, 24 neutrons, 24 electrons, and an atomic weight of 48. In
comparison to oxygen, where atoms are linked in a straight line, the ozone molecule is bent at a bond angle of 116.8°, a configuration that makes the ozone molecule more electrically active.

Consequences of Ozone Properties


  • Short half-life; Must generate ozone on site with ozone generating equipment. 
  • Ozone must be used shortly after it is produced.  Therefore, the ozone equipment must be sized for the peak ozone demand.  In systems where high levels of ozone are required for short periods of time the ozone equipment must be sized for that peak demands as no buffer, or storage of ozone is possible.

Partially Soluble Gas

  • Requires mechanical gas/liquid contacting.  While ozone is more soluble in a liquid than oxygen, it will still require contact basins, venturis, or other devices to mix ozone into water. 
  • Ozone has the tendency to off-gas back out of liquid causing safety concerns.  Ozone Solubility Info Here

Strong Oxidant

  • Material compatibility can cause problems – list of acceptable materials is short
  • Secondary reactions must be considered

Detection – difficult to monitor

  • Ozone breaks down upon contact with sensor cell.
  • Ozone has low vapor tension, does not fill room uniformly
  • Leaks can be difficult to find


  • Short-term health hazards with ambient ozone

Due to the unique properties of ozone, there are distinct advantages and disadvantages of ozone use in the industry.

Advantages of Ozone

  • Strongest disinfectant available
  • Strongest oxidizing agent available
  • Is environmentally friendly
  • Adds no chemicals (no chemical storage)
  • Unstable – Leaves no residual (only oxygen)
  • Allows ozone-advanced oxidation OH-
  • Can lower overall operating costs

Disadvantages of Ozone

  • Unstable – must produce as needed (makes advantage to Health care)
  • Gas-liquid contacting equipment is required
  • Generation/contacting can be complex, difficult to control
  • System must be designed with personnel safety in mind