The Color of Ozone

Does ozone gas have a color? Yes, the color is blue. The problem is, ozone is normally found in gas, or in water at such low concentrations that the color is not visible.

Recently we performed some lab testing that required ozone levels in water greater than 100 ppm. The picture below provide some great examples of the color of ozone.


ozone color
0 ppm ozone on left vs >100 ppm ozone on right


Ozone in water
The Color of Ozone is visible in this image


ozone in water
An ATI Q45 Dissolved Ozone Monitor was used to measure dissolved ozone in water. The blue color of the water is even slightly visible in the flow cell used to measure ozone.


Dissolved Ozone in water
AS the dissolved ozone level increases the color of the water gets darker. The blue color in the water starts to become visually evident above 50 ppm.


Ozone levels in water turn water blue
The blue color of ozone is more visual in larger containers like this 1-gallon water jug.


Ozone Properties

The table below provides additional information on the properties of ozone. This shows the color of ozone is light blue, which is true. It is only visibly blue when ozone gas or ozone in water is at a very high concentration.

Property Ozone Oxygen
Molecular Formula O3 O2
Molecular Weight 48 g/mol 32 g/mol
Color Light blue Colorless
Smell Odor threshold of 0.001 ppm, pungent at high levels Odorless
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 Pressure 54.5 atm 5.043 atm
Density 2.144 g/l @ 0 deg C 1.429 g/l @ 0 deg C
Solubility @ 0 deg C 0.64 g/100 ml 0.049 g/100 ml
Electrochemical Potential 2.07 V 1.23 V


Ozone Solubility

Ozone is only partially soluble into water. The graph below shows the solubility of ozone into water based on water temperature and ozone gas concentration. As the water temperature decreases and ozone concentration increases ozone becomes more soluble into water.

Water pressure is the third and final factor in determining ozone solubility into water. However, as these images were taken of water at ambient pressure, this was not a factor used, and is not a required factor in achieving high ozone levels into water.

Do you have a need to achieve higher ozone levels into water? Or lab testing that requires dissolved ozone levels higher than off-the-shelf equipment can provide? Give us a call, we would be glad to help.


Tech Tip – How to dissolve ozone into water – solubility

Ozone is commonly dissolved into water for water treatment, or for water to carry ozone for other jobs like sanitizing surfaces or produce.  In fact, many of the applications of ozone require ozone to be dissolved into water.

Ozone is normally produced as a gas from oxygen in air, or concentrated oxygen.  That gas must then be dissolved into water.  As ozone is partially soluble into water it is possible to dissolve ozone into water but does require the proper equipment to be efficient.

As producing ozone requires equipment and electricity, there is a cost for every gram of ozone produced.  Therefore, there is value tin ensuring every gram possible is dissolved efficiently into water with as few losses as possible.

How easily ozone dissolves into water is based on the solubility of ozone into water.  Learn more about ozone solubility here.

The solubility of ozone into water is the ratio of ozone that will dissolve into water, and the overall capacity to dissolve ozone into water.  The solubility of ozone into water is based on Water Temperature, Ozone Concentration, and Water Pressure.  See image below for a visual example of how ozone concentration and temperature affect ozone solubility.

Ozone dissolves into water based on solubility
Ozone Solubility into water based on water temperature and ozone concentration

The chart above shows the maximum ozone concentration in water possible for a given water temperature and ozone concentration.  The higher the max ozone concentration, the easier it will be to dissolve ozone into water.  The lower the max concentration (solubility) the harder it will be to dissolve ozone into water as the excess ozone will simply off-gas and be wasted.

See this information in chart form:

chart of ozone solubilty into water
Chart of ozone solubility based on water temp and ozone concencentration

Pressure also affects ozone solubility.  Increased water pressure will push ozone gas into the water more efficiently.  This is a linear affect, more pressure =  higher solubility factors.  See chart below for visual example.

how water pressure affects ozone solubility
Ozone Solubility based on water pressure


  • Higher ozone concentrations = higher dissolved ozone levels in water
    • ozone generators that produce ozone at higher concentrations will dissolve ozone into water more efficiently than those that produce the same amount of ozone at a lower concentrations
    • ozone production in g/hr is not as important as concentration
    • Look for higher % by weight, or g/m3 numbers
  • Lower water temperatures = higher dissolved ozone levels in water
    • Colder water dissolves ozone easier
    • adding ice cubes to small volumes of water will increase dissolved ozone levels
  • Higher water pressure = higher dissolved ozone levels in water
    • If bubbling ozone into water use taller columns, the water at the bottom of the column (where the diffuser is) will be under higher pressures
    • when using venturi systems ensure the contact tank is under some pressure.

Learn more about ozone solubility and how you can apply this information to your application at the link below:

Ozone Solubility into water