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Chemistry gets everywhere (Image: Katja Kircher/Getty)

Every moment of every day, chemical reactions are taking place in the air and on almost every surface of our homes. The primary driver of this indoor chemistry is ozone, a highly reactive molecule made up of three oxygen atoms. Most of it comes into our homes from outside, although relatively small amounts come from air purifiers, laser printers and heating, ventilation and air conditioning (HVAC) systems.

It doesn鈥檛 hang around for long. 鈥淚ndoor ozone tends to be much lower concentration than outdoor ozone, but that鈥檚 because it reacts with so many things indoors,鈥� says at the University of Texas. 鈥淪o there鈥檚 a lot of interest in ozone reaction products.鈥�

Ozone reacts with anything scented, such as air fresheners and cleaners. 鈥淎ll of those scented compounds have carbon-carbon double bonds and ozone loves to attack those things,鈥� says Corsi.

The proliferation of fragrances in our homes means that, in some cases, the chemistry is unknown. 鈥淲e are using so many scents indoors these days and when they oxidise they form things we just don鈥檛 find outdoors,鈥� says Corsi. 鈥淣o one has done the toxicology on them.鈥� He says we should be paying attention to peroxides and dicarbonyls because they have a similar structure to other chemicals known to be toxic or cause severe irritations. 鈥淭here are red flags flying all over the place,鈥� he says.

Ozone attacks the carbon-carbon double bonds elsewhere too 鈥� in the styrene in our carpets, in our soaps and even in the oils on our skin. It leads to the formation of carbonyls, including formaldehyde, the pungent gas used as a preservative in mortuaries. 鈥淚n high enough levels it can cause upper respiratory problems and eye irritation, that kind of thing,鈥� says Corsi. Other short-lived molecules called Criegee biradicals are also produced by ozone chemistry. These are extremely reactive and lead to the formation of a wide range of by-products, including some that are irritants or toxic.

A move towards greener living doesn鈥檛 help. Many 鈥渘atural鈥� cleaning products contain terpenes or terpenoids, organic molecules found in plants that are highly reactive with ozone. 鈥淭ighter, more draft-resistant homes and more green products have led to our homes becoming intense chemical reactors,鈥� says Corsi.

Many indoor pollutants are released into our homes by the things we bring into them. Formaldehyde, for example, comes from the likes of plywood and cosmetics. There鈥檚 also the release of semi-volatile organic compounds, such as the flame retardants used in furniture and bed mattresses.

However, certain materials soak up what鈥檚 been released and the products of indoor chemistry. 鈥淭he polyurethane foam that鈥檚 often used in furniture and as foam padding beneath carpet is a tremendous sink for pollutants,鈥� says Corsi. As is the gypsum plasterboard that lines many of our walls.

The weather inside our homes (see 鈥�Cold front in the kitchen鈥�) has a big impact on pollution levels. The high temperatures sometimes found in the spaces between walls speed up the rate of chemical reactions. 鈥淎s a really rough rule, if you increase the temperature of a material by 10 掳C, you are going to double the emission rates from it,鈥� Corsi says. And when the temperature rises, so does the pressure in the spaces 鈥� pushing the dirty air into our rooms. 鈥淓lectrical outlets and cracks in the walls are really leaky,鈥� says Corsi.

Read more: 鈥�The secret life of your home鈥�

This article appeared in print under the headline 鈥淚ndoor chemistry鈥�