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This question regarding an ionizer in an Asus laptop has a little bit of information about air ionizers (air ionisers for those using UK English), but not a lot at the time of writing.

There are various claims around the place about the benefits of using an air ionizers, such has helping people sleep better, being "vitamins of the air", and cleaning particulates from the air.

I also found a claim that ionizers will turn your walls black, and a warning that "spark discharges may cause dangerous ignitions" in some circumstances.

Are there any substantial benefits or risks to using an air ionizer, supported with good evidence?

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This question is little broad at the moment. If someone finds evidence that, say, people do sleep better, but fails to find out that, say, one brand has a habit of exploding in a ball of flame, would you accept that as an answer? Is that better or worse than someone answering with the opposite info? Requiring people to establish ALL of the benefits and ALL of the risks is probably too broad. Alternatively (preferably!?), choose one of the claims, and put each other one in a separate question. –  Oddthinking Feb 10 '12 at 4:26
    
I just looked at the "spark discharges" page. It was referring to "explosive or flammable atmospheres" - running any electric motor not made for those conditions is probably a bad idea. Running a moving plastic (?) rotor that builds a static charge is even worse. Hardly counts as a substantial risk though. –  Oddthinking Feb 10 '12 at 4:32
    
@Oddthinking, to start with, I'd be pretty happy to find a single benefit of substance - eg an effect that's shows enough benefit to buy a machine, at least under some circumstances. Clarifying individual benefits separately is detail that should come later, in my view. –  Highly Irregular Feb 10 '12 at 5:06
    
Regarding sparks, it's hard to know just how explosive a substance would need to be before there's a risk. A kitchen that's dusty with flour might be a relevant example in a home situation. Given the nature of the device (has an exposed, charged surface), I'd worry that risk would be higher than with, say, use of an electric mixer (staying with the kitchen example!). –  Highly Irregular Feb 10 '12 at 5:09
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The ionizer actually reduces the chances of static sparking by making the air dissipative (that is, conductive at a low level). Ionizers were always a standard appliance on the ESD-sensitive workbenches I worked on in aerospace labs (along with the humidifiers, bracelets, static mats, bonding straps everywhere and so forth). –  Stan Rogers Feb 10 '12 at 20:36

1 Answer 1

I am somewhat surprised by the findings, but there is a lot of published research on this topic.

A paper published in Science in 1976 maintains that:

There is convincing evidence that both negative and positive ions (i) inhibit growth of bacteria and fungi on solid media; (ii) exert a lethal effect on vegetative forms of bacteria suspended in water when opportunity is provided for contact of cells and ions; and (iii) reduce the viable count of bacterial aerosols

Moreover, the same paper concludes that "in the case of mice infected with influenza virus, ion-deprivation increases the cumulative mortality rate" and "since ion depletion is a constant concomitant of modern urban life, one reasonably may speculate about comparable inimical effects on humans."

A study published in the Journal of Applied Microbiology in 2009 finds ionization "to be an effective method for reduction in surface and airborne bacteria." In this study ionizers were installed inside refrigerators, and although effective the amount of reduction depended "the constructional layout and material properties of the ionizer housing, air circulation within the refrigerator and the interior volume" or the refrigerator.

An earlier study in the Journal of Food Protection concludes that "high levels of negative air ions can have a significant impact on the airborne microbial load, and that most of this effect is through direct killing of the organisms."

By contrast, a study done in 2007 by the School of Civil Engineering, University of Leeds suggests that "the bactericidal action attributed to negative air ions by previous researchers may have been overestimated."

To summarize then, it seems that ionizers can indeed reduce the airborne bacterial load but could also be bad for humans. A reasonable piece of advice comes from the same 1976 article in Science quoted above, which recommends to "maintain air ion concentrations and ratios approximating those existing in nature" and expresses hope that "air ion levels of urban air will approach those of clean rural air."

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Thanks for the answer! Is there any one paper in particular that says they could be bad for humans? It's not clear where you got that idea from. Thanks –  Highly Irregular Mar 11 '13 at 22:00
    
@HighlyIrregular The human stuff comes from the 1976 Science article. I added the citation explicitly. –  denten Mar 11 '13 at 22:18
    
Ok, thanks, that wasn't clear. –  Highly Irregular Mar 11 '13 at 22:52
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No problem! If you read the article you'll see that the human conclusions are speculative (based on mice). –  denten Mar 11 '13 at 23:14

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