What is ozone?

11 September 2018

Question

What is ozone? We also hear that it’s bad for the environment, but does it have any benefits?

Answer

Chemist Pether Wothers takes a sniff at this question from listener, Garth. 

Peter: Ozone is a form of oxygen. Now of course, we breathe in oxygen every day, all the time to stay alive. But the gas that we are breathing in is composed of two oxygen atoms united. So this is an oxygen molecule with the formula: 02.

Ozone is a different form of oxygen where actually three of these atoms of oxygen are united together. And this has completely different properties. This is poisonous and it's poisonous because it's too reactive for us.

Ozone can be used as a disinfectant, for instance. It is incredibly reactive, in the same way that bleach is very reactive; it can destroy tissue and so on. This is the sort of action that ozone will have on our bodies if we breathe this in or are exposed to it in high concentrations. But it can be useful. Of course everyone's heard about the ozone layer and that's a slightly different thing. This is actually partly used to protect our environment from ultraviolet light that would otherwise be hitting the earth. But ozone itself in low concentrations can be used. So, for instance I was walking into a toilet the other day and there was this very strange smell, and I thought, this must I must be ozone! I thought, am I going mad here or is this really ozone that I can smell?

Chris: Well, it was a toilet Peter.

Peter: (laughter) Well indeed! It was a toilet, yes but eventually I looked around and found at long last, this ozoniser that had been stuck on the wall. There are now companies that are making these things because it's actually a very easy form of disinfectant, because you can produce ozone in small concentrations, simply by passing an electrical discharge through oxygen -a spark

Chris: And what does that do to make the ozone, then?

Peter:  The energy from the spark will rip apart O2 molecules and then you will, for a short period of time, get these incredibly reactive oxygen atoms. Now they don't want to stay like that, which is why we would of course, be normally breathing in O2 where two of them have bonded together, and maybe, if these two oxygen atoms find each other, they will reform an O2 molecule. But of course it's far more likely that one little oxygen atom will bump into another oxygen molecule rather than the other part that just fell apart. And so that would then form an O3 molecule. And so actually this is why anywhere that there’s a spark, regular sparks, you can sometimes smell this sort of slightly peculiar smell...

Chris: Like when you use power tools for example, a drill, or a hand blender, or hair dryer.

Peter: Or dodgem cars.

Chris: Dodgem cars! Yes, you get that very distinctive smell and that’s ozone is it?

Peter: It could be ozone, It could also be... so when you spark through air, of course air that we breathe in is not just O2 molecules, there’s a lot of nitrogen in there. The main gas is nitrogen, and so the other thing that you can easily form are oxides of nitrogen and those also have a rather peculiar smell. So sometimes, it’s not quite clear whether we are smelling the ozone or the nitrogen oxides.

Chris: and just returning to your former example: Did the ozoniser in the toilet help to neutralise nasty niffs or not?

Peter: I’m not sure whether it was for nasty niffs, or for any potential pathogens to some degree, if they are sort of just on the surfaces. But it certainly smelt better than usual!


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