What is this carbon dioxide stuff anyway?

by Simon Handby in At home on 20.03.08

While writing our earlier Lotus post, it occurred to us that everybody does a lot of talking about carbon dioxide, without ever really reminding us what the stuff is. So, for anyone who was having a quiet doze during school chemistry lessons, here’s a quick refresher.

Carbon dioxide is a colourless, odourless gas that’s present in the air we breathe, although it makes up just a tiny fraction of it. There’s rather more of it dissolved into a fizzy drink – it’s what unruly children burp up if they drink too much pop.

Most organic matter (and the fuels derived from it) contains large quantities of carbon, and when it burns this gets combined with oxygen to produce a lot of CO2. The gas’ moniker comes from the fact that each of its molecules is made up from one carbon (C) atom, bonded to two oxygen (O) atoms. It’s not to be confused with toxic carbon monoxide which is produced when there’s not enough oxygen around - its molecules contain only one oxygen atom.

Carbon dioxide is also released as waste when living things extract energy from their food, which is why we breath the stuff out in higher concentrations than we breath it in. With so many of us belching it out, levels would quickly build up, but plants use the gas as a building block for the sugars they produce during photosynthesis, removing it from the atmosphere almost as quickly as it’s produced.

Still with us?

CO2 also has a couple of unusual properties. Unlike most other gases, it’s never found as a liquid at normal pressures. Dry ice – beloved backdrop to 80s photo shoots – is frozen carbon dioxide. The groovy vapour is produced as it heats up and turns directly into a gas - a process known as sublimation.

In the atmosphere it’s also a greenhouse gas; absorbing heat from the sun that bounces back off the earth’s surface, and reflecting some of it back downwards. Without this effect, the earth would be too cool for us to live on, but CO2 levels have increased markedly since the industrial revolution, increasing the amount of heat that gets trapped by the atmosphere - it’s one of the main factors thought to cause global warming.

IMAGES

While looking for pictures to illustrate this post, we happened on these amazing shots by Flickr user jurvetson. They’re pictures of an art-come-science exhibit by Shawn Lani that pitched chips of dry ice into a bowl of water. There’s some stunning video of Icy Bodies on the Shawn Lani Studios website.