ARI SHAPIRO, HOST:
In India, there is money in the air, specifically there's money to be made fighting air pollution. New Delhi has some of the worst air of any city in the world. The other day, I met a man in Delhi selling an American-made product, a necklace that he said would protect its owner from air pollution - the secret, negative ions.
It's negative ions?
UNIDENTIFIED MAN: Yes.
SHAPIRO: And how does that filter out particles from the air?
UNIDENTIFIED MAN: So basically negative ions are emitting from this particular black brush.
SHAPIRO: But does it actually take particles out of the air?
UNIDENTIFIED MAN: Yes. It will with the help of negative ions it will distract all the viruses, VOCs in your breathing space.
SHAPIRO: Is that really scientifically true?
UNIDENTIFIED MAN: Yes.
SHAPIRO: That sounds very suspicious to me - the negative ions filter the...
UNIDENTIFIED MAN: See negative ions is emitting negative ions from this black brush. It is distracting viruses, bacterias for entering your breathing space. This is how it happens.
SHAPIRO: As you can hear, I was not exactly convinced, and these necklaces are for sale all over the place, not just in India. So we've asked NPR science correspondent Geoff Brumfiel to come into the studio for a bit of a fact check.
GEOFF BRUMFIEL, BYLINE: Hi there.
SHAPIRO: What exactly is a negative ion in the first place?
BRUMFIEL: So basically it's when you take a particulate that's in the air and you add a negative charge to it so it's got a static charge on it.
SHAPIRO: And does it have any air-filtering properties that are grounded in science?
BRUMFIEL: So I actually went to an air quality expert, a guy named Sergey Nizkorodov at UC, Irvine - I asked him that. And his answer was yes. Actually there is some scientific fact to this. If you charge particles and then you pass them through a filter, it's easier to catch them in a filter. It's not quite as effective as some other types of filtration, but negative ion filters - you see them advertised like in airplane catalogs and stuff. And they can provide some help especially in an enclosed environment.
SHAPIRO: OK. So I can imagine one room getting filtered with one of these devices that's a bit larger, but wearing a pendant on your neck as you're just walking around outside. How can that have any positive impact on the air that you're breathing in?
BRUMFIEL: Well, yeah, I mean, that's the bottom line. A big tower like some of our listeners might have in a room works. Wearing it around your neck, though, our experts say that's not going to do much of anything. I mean, the fact is without something directly over your face - you know, a mask - you're not going to filter much in the way of city pollution now.
And, in fact, I mean, if this thing actually does work as advertised, the expert I contacted said it might not be a good thing. It might actually be generating small amounts of ozone which is hazardous to breathe in. Compared to Delhi air, I doubt it's much of a problem, but basically it doesn't work. And if it does, it probably isn't the best thing to wear around your neck.
SHAPIRO: NPR's Geoff Brumfiel, thanks a lot.
BRUMFIEL: Thank you. Transcript provided by NPR, Copyright NPR.