Hydroxyls vs. Ozone

Pyure Safety

Maintaining Safe Levels

Why Ozone Levels Plateau

Hydroxyls vs. Ozone

Pyure Technology uses UV energy to produce hydroxyls from water vapour, a process that also produces very small quantities of ozone as a byproduct. The sanitization power of Pyure Technology is driven by hydroxyls, not ozone. Hydroxyls are a million times more reactive than ozone.

Pyure Hydroxyl Production

It takes only a few parts per billion of hydroxyls to rapidly sanitize a space. Pyure devices produce hydroxyls at the same rate as nature.

Organic oxidants are formed when hydroxyls react with ambient volatile organic compounds (VOC) and oxygen. Organic oxidants are more stable than hydroxyls, allowing them to circulate through a treated space.

Hydroxyl Production Levels

Pyure Ozone Production

The quantity of ozone produced by a powerful Pyure portable device (The Odorox® Boss™ model) is 0.041g per hour.

To put this ozone production level in perspective, commercial ozone generators typically produce
40 to 400 grams of ozone per hour, which is 1,000 to 10,000 times more ozone than the Pyure unit.

Ozone Production Levels

Reaction Rates

Hydroxyls are the most powerful naturally occurring oxidant on earth. The sanitizing organic oxidants Pyure produces are also powerful, reacting much faster than ozone. Ozone concentrations would need to be much higher than the levels Pyure produces to have a sanitization effect.

Pyure Safety

Pyure Portable, In-Duct and Wall-Mounted products are engineered to produce safe levels of total oxidants (including ozone) when operating guidelines are followed. Pyure custom solutions continuously monitor and control oxidant production through the use of electrochemical sensors.

Maximum Ozone Levels

Pyure sets the total oxidant (ozone + other organic oxidants) limit for its portable, In-Duct and Wall-Mounted devices at 50 parts per billion for three reasons:


The limit for continuous, 8-hour exposure to ozone is 100 parts per billion, according to OSHA

2Pathogen Protection

At these safe levels, Pyure has proven that the hydroxyls and organic oxidants produced kill pathogens and neutralize VOC

3Ozone’s Inertness

At these safe levels, ozone has no effect on VOC or pathogens

Maintaining Safe Levels

Pyure Operating Guidelines - Minimum Treatment Area

For portable, In-Duct and Wall-Mounted units that have no built-in sensors or controls, Pyure has conducted extensive testing to determine the volume of space that each device can treat safely and effectively. The concentration of ozone is a function of the volume of treated space: the smaller the volume, the higher ozone levels will be.

While Pyure recommends only using its devices in well ventilated areas, these operating guidelines indicate the minimum size room, in the absence of any ventilation, that will ensure ozone levels stay below 50 parts per billion.

Pyure Operating Guidelines - Optimal Treatment Area

Pyure has operating guidelines for each of its portable, In-Duct and Wall-Mounted units that provide a range of safe and effective volumes to treat. These guidelines are based on:

  • Measurement of ozone levels in various sized spaces
  • Hydroxyl production of each Pyure device
  • Published reaction rates of hydroxyls with VOC
  • Ventilation rate of three air exchanges per hour

Pyure Custom Solutions

Pyure does not provide operating guidelines for its custom solutions because they have interactive process controls that ensure ozone levels are always safe and organic oxidant levels are always effective.

  • Custom solutions are equipped with ozone sensors in various locations within a treated space.
  • Sensors communicate with a control system that ensures that total oxidant levels (including ozone) stay within a narrow band set by the user.
  • The system monitors total oxidant levels continuously: if levels approach the maximum, the hydroxyl generator output is cut back or shut off. If the total oxidant levels approach the minimum, the hydroxyl generators increase their output to raise levels.

Note that indoor ozone levels alone are not an accurate measure of hydroxyl production because they are a blend of ozone generated from the Pyure device and ozone introduced from outdoors. In urban areas, ambient ozone levels can exceed the limit set for the Pyure device. In these circumstances, end users should consult Pyure specialists to determine the appropriate operating conditions and limits to set on custom solutions.

Why Ozone Levels Plateau

Because Pyure devices produce ozone at a constant rate, and ozone is very slow to react with VOC, it is sometimes falsely assumed that ozone levels will progressively build up in a treated space over time and reach unsafe levels if the device is operated continuously.

Ozone Plateau Effect

  • MySpace
  • MDU/Rx™
  • Slimline
  • Boss™
  • Boss XL3™

This is not the case: ozone levels quickly reach a plateau, after which time they no longer increase.

There are two reasons for this plateau:

  • Pyure devices produce very low levels of ozone
  • Ozone loss rates from surface deposition are approximately 70%

Numerous Pyure studies have demonstrated that ozone levels reach a steady state plateau where ozone levels no longer increase, even in the absence of any ventilation. This is because ozone loss modes due to surface deposition are high and continuous. Air exchange will further reduce ozone levels. Ozone losses due to adsorption occur when ozone comes into contact with carpets, furniture, painted surfaces, floor and ceiling tiles, clothing, and other materials. This ozone loss mode is continuous at a rate proportional to the total surface area within the treated space. For each Pyure device in a room of sufficient size, the production rate and loss rate will be equal, resulting in a plateau where ozone levels no longer increase.

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