What is Ozone.
Ozone is a naturally occurring gas, produced in the upper atmosphere by ultraviolet light from the sun. It comprises of nothing but oxygen in the form O3, that is to say that each molecule contains 3 atoms of oxygen (Tri-oxygen). Oxygen in this form is a very unstable gas, as three atoms of oxygen will not bond properly, and it looks to shed the extra atom at the earliest possible opportunity, it is this that make ozone good at killing odours, bacteria, and fungi spore etc., but this also makes it very corrosive if concentrations are too high. In its normal state high in the atmosphere it is the only thing that protects the earth from the very harmful ultraviolet rays from the sun, the very thing that creates it. It can of course also be created artificially, either by ultraviolet light, or high voltage electrical corona.
How does ozone work?
Because of its instability, ozone is a very powerful oxidant, it readily decays into O2, releasing a single oxygen atom from each of its molecules. As oxygen cannot exist as O1, this loose oxygen atom must instantly bond with any other molecule that will accept it. These other molecules can be from bacteria (resulting in it's destruction), or an odour. Oxygen atoms can also bond with many other things like metal surfaces, volatile compounds, and other gasses. Finally of course 2 loose oxygen atoms can combine to revert back to their original state 02. If we have an ozone generator running in a room, the ozone will only build up to a certain level, at this point the ozone will deplete as fast as it is generated, either reverting back to oxygen or oxidizing surroundings. Thus the level of ozone will vary depending on the surroundings e.g. room size, air changes, temperature, humidity, level of bacteria/volatile substances/odour, and reaction with surrounding surfaces. It is therefore important to be able to control the output of any ozone generator.
What is the right level of ozone?
Ozone has been shown by extensive laboratory trials to be effective at reducing bacteria and odour when used at levels no higher than 0.05ppm. These levels are considered safe to breathe 24 hours per day. Tests have also shown that at these levels there is no harmful effect on plants. By controlling the amount of ozone generated it can be used safely and effectively to destroy unpleasant odours and control bacteria.
In the UK there is no time limit of occupational exposure to ozone levels of below 0.2ppm. In many European countries there is an eight hour time weighted average exposure limit of 0.1ppm while in the U.S.A. the comparable level is 0.08ppm. The World Health Organization has an average Air Quality Guideline of 0.05 - 0.06ppm measured over an eight hour period.
Obviously without some very sophisticated and expensive equipment it is difficult to determine these levels very accurately if at all. As a rough guide, a pleasant fresh smell would indicate levels of around 0.025ppm. When the smell becomes unpleasant then levels would probably be reaching about 0.10ppm. By the time it is becoming uncomfortable and irritating the throat, this would be about 0.50ppm, and by the time it starts to make you feel really ill with breathing difficulties, bad throat and nausea levels could be reaching 5ppm, at this level it can also be harmful to plants. At higher levels than this (generally about 25ppm or more) it can become toxic.