I am trying to understand what happens inside various types of air ionisers.

Some of them are sold for their purported health effects (which I do not want to discuss here), another type are used in industry to control electrostatic charges on surface of materials. Also there are some natural processes where oxygen form is modified by electric current namely thunderstorms.

Can an oxygen molecule be broken by placing it into a strong external electric field?

If yes how is it possible because as we know the oxygen atoms in molecules are bonded by a non-polar bond?

What are possible by products of this process (even temporary one)?

I assume that air is composed only from oxygen (no nitrogen, argon, carbon dioxide etc.).

  • $\begingroup$ Why negative vote ? These kinds of things happen in real world during thunderstorm, also in laser printer. As we know quite well ozone is enviromental toxine detrimental to health. I want to understand whole process leading to production of ozone (and potential other by products even temporary ones if there are some) to be able to control it. It is of uttermost practical importance. Sorry that I have not master degree in chemistry like most of you and 20 years of practice. This is interdisciplinary question related to electromagnetics which I am more familiar with. $\endgroup$ Commented Jul 17, 2016 at 8:46
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    $\begingroup$ It was probably downvoted because it is just a big wall of text. Consider formatting it into paragraphs and using better punctuation and grammar. Also, add some better tags. It is also a rather broad question. Consider breaking it down into several more focused questions. $\endgroup$
    – bon
    Commented Jul 17, 2016 at 8:52

2 Answers 2

  1. Yes, an oxygen molecule (much like any other molecule) can be broken by electric field alone.
  2. No, it won't be broken into separate oxygen atoms, precisely because the atoms are neutral and the bond between them non-polar, like you said. Instead, it would be broken into $\ce{O2+}$ and an electron.
  3. This is not important anyway, since it would require electric field much stronger than those present in air ionizers.

What happens in air under voltage, then? Well, air always contains some ions from whatever sources (cosmic rays, background radiation, etc). As you apply voltage, your positive and negative ions start speeding up in the opposite directions. Once the voltage is high enough, they accelerate to the point that they might break neutral molecules by bumping into them. In doing so, they produce more ions, and those do the same, so pretty soon there is a breakdown going on. You see a blinding spark, the fuses blow up, the voltage shuts off, and the ions start to recombine into molecules. As luck would have it, sometimes they combine into $\ce{O3}$ - that's an important source of ozone both in nature and in the lab.

In fact, the situation is much more complicated. Gas discharge does not have to be that dramatic. It comes in various forms, some of them pretty controllable.


Several things can happen to O2 molecule when it is placed in electric field.
(1) Two ozone molecules can form from three dioxygen molecules. Ozone is more deadly than chlorine, so the resulting gas can be used as a bactericide.
(2) A needle under high negative voltage will leak electrons in the air. Some of these electrons will bind to O2 forming an anion-radical O2*-. This is a reactive oxygen species (ROS) that allegedly have some good health effects.


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