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’t hang around for long. “Indoor ozone tends to be much lower concentration than outdoor ozone, but that’s because it reacts with so many things indoors,” says at the University of Texas. “So there’s a lot of interest in ozone reaction products.”
Advertisement
Ozone reacts with anything scented, such as air fresheners and cleaners. “All of those scented compounds have carbon-carbon double bonds and ozone loves to attack those things,” says Corsi.
The proliferation of fragrances in our homes means that, in some cases, the chemistry is unknown. “We are using so many scents indoors these days and when they oxidise they form things we just don’t find outdoors,” says Corsi. “No one has done the toxicology on them.” 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. “There are red flags flying all over the place,” he says.
Ozone attacks the carbon-carbon double bonds elsewhere too – 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. “In high enough levels it can cause upper respiratory problems and eye irritation, that kind of thing,” 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’t help. Many “natural” cleaning products contain terpenes or terpenoids, organic molecules found in plants that are highly reactive with ozone. “Tighter, more draft-resistant homes and more green products have led to our homes becoming intense chemical reactors,” 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’s 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’s been released and the products of indoor chemistry. “The polyurethane foam that’s often used in furniture and as foam padding beneath carpet is a tremendous sink for pollutants,” says Corsi. As is the gypsum plasterboard that lines many of our walls.
The weather inside our homes (see “Cold front in the kitchen“) has a big impact on pollution levels. The high temperatures sometimes found in the spaces between walls speed up the rate of chemical reactions. “As a really rough rule, if you increase the temperature of a material by 10 °C, you are going to double the emission rates from it,” Corsi says. And when the temperature rises, so does the pressure in the spaces – pushing the dirty air into our rooms. “Electrical outlets and cracks in the walls are really leaky,” says Corsi.
Read more: “The secret life of your home“
Not so fresh air
Three unexpected pollutants
Dishwashers
Dishwasher detergent can contain sodium hypochlorite and when it reacts with some foods, particularly meat and tomatoes, the result is chloroform.
Scented candles
The slow-burning scenting agents only have a millisecond to burn in the flame and often don’t burn completely. Many lead to the formation of ultra-fine particles that can find their way into our lungs.
Vacuum cleaners
The wheels flick up particles that contain allergens and pollutants into the air.
This article appeared in print under the headline “Indoor chemistry”
