By making your house smell nice you are also making it filthy. Though it may make a house smell clean, secretly, most air fresheners fill the house with tiny particles of dust — all thanks to limonene.

Limonene has been featured before on this site — it’s a liquid hydrocarbon that turns an orange peel into a flamethrower. This use is generally discouraged around the house, but limonene is very much a household staple, as it’s a natural insecticide and a gentle solvent for substances like paint. Mostly, though, it’s used to smell up the place. Limonene smells like oranges. (Or most of the time it does; some forms of limonene smell like pine.) Companies use it to add fragrance to cosmetics, perfumes, and air fresheners.

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Something very weird happens when limonene hits ozone — the molecule, which contains 10 carbon atoms and 16 hydrogen atoms in a roughly hexagonal structure, goes through ozonolysis. Ozone, which is a volatile trio of oxygen atoms, breaks the limonene up into secondary fragments, which then recombine with oxygen into solid particles. With gas and liquid, you are making solids.

Exactly how much dust you make depends on a lot of things, including the presence of UV radiation and the amount of nitrous oxides present. (Nitrous oxides are any of a group of molecules that combine nitrogen with one, two, three, or more oxygen atoms.) What most affects the production of these particles is the amount of ozone and limonene, and lately humans are producing a lot more of them both.

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These particles are roughly 0.1 to 0.3 micrometers wide — too small to be seen with the naked eye — but they’re there. Any time your citrus-scented air freshener squirts out fragrance on a smoggy day, you’re creating tiny particles in your air. Fortunately, when it comes to making your house smell nice, harmless submicron particles are just about the lowest price anyone could be forced to pay. It might give you a little more to do around the house, but when you clean up, at least you can take pride knowing you’re being an alchemist.

[Via The Secret Life of Dust, Secondary Organic Aerosol Formation of Limonene Ozonolysis]

Image: Shutterstock, Africa Studio.

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