PRESENTER: Today I'm going to show you how particles can come from gases. So what I have here is I have an artificial atmosphere right here, a glass jar. I have a light source in there, which will act like the sun, so here's the sun right here. I'll set the sun. Sun's off right now. And then I have a source of gases, an orange. So let me first peel the orange. Let's peel the orange here. A little bit of orange. Take some peel off the orange. OK, that's enough.

So now here we have some orange peel. That smells really good. So what I'm going to do is take some orange peel and squeeze it a little bit, and I'm going to drop it in the atmosphere. Squeeze some more and drop it in the atmosphere. Now I'll put the lid on the atmosphere. OK. There we go. Now you see I have orange peel here and so there's some gases that smell really good, these volatile organic compounds. So I can smell, and they smell great.

And I'm going to show you that even though I put that in there, I have a light source. Here's a little laser, just a laser pointer, and you see I'm shining it in there and you don't really see any particles at all in here. So look in here and there are no particles. See that? No particles.

OK, now I'm going to turn on the sun, which is this nice ultraviolet light here. So I'll turn on the sun, and we're just going to wait a little bit. So the sun is on. You can see it glowing here and here. And so what that's doing is that's producing lots and lots and lots of OH, the hydroxyl radical. And it's also producing lots of ozone, and so it's doing what the atmosphere does, which is oxidizing the volatile organic compounds that came from the orange peel.

Those volatile organic compounds, one of the main ones is called limonene, which is of course also in lemons and limes. And so we are just going to let that cook a little bit and let the day go on a little bit. And then what we can do is we can see if we're making any particles.

So let me shake it up a little bit like there's a little bit of a wind. There we go. So now you see we have a very bright light from the lamp. It's really gotten bright. And we can see that it's doing a lot. Heat it up a little bit more. Now we'll just take a quick look and see if we see anything. So the laser light here we can't see anything in the atmosphere outside of the chamber, so I'm shining it. Right now this is hitting my hand, as you see here. And there's no sort of scattering.

But I've turned off the light now. Now we shine this in here, and we see a tremendous beam. And so all this is small particles that we made which are now scattering that light. See you can see that very strong beam. And all those particles came from the volatile organic compounds, limonene and others, that came out of the orange peel and then they were oxidized in the atmosphere to make less volatile compounds, one that had lower vapor pressure, and then those all stuck and made these nice little particles that you see here. So there's a demonstration of gas to particle conversion.