I live about 15km/9miles from central London, which is about an hour by the fastest public transport and about 35minutes by bicycle. The bike's free, and it's a helluva lot more flexible – you can pretty much just rock up right outside wherever you're going, no parking fee, no walking, plenty of exercise. Sweet.

So what's the catch? The air. You breath a lot of it, and it's full of shit. To give you some idea exactly how foul it is, check out a brand new cycling filter, and one that's had about 500km-worth of air sucked through it.

When it's new the air tastes better; there's no doubt it's working. A pleasant side-effect of having a mask is keeping warm in winter. Diffusing the air through the (slightly moist) mask seems less harsh on the throat too.

Here's a cut-away of the one on the right. Look closely at the left-hand edge how toward the bottom where the filter meets your cheek there's no airflow it's pretty much white, whereas toward the middle breathing area it's clogged with collected vehicle exhaust fumes.

The thin black line is a carbon filter that's fitted to the top-end Techno Gold filters from Respro. These filters "work on the basis of adsorption and chemisorption of organic vapours and acid gases" like hydrocarbons, the various nitrogen oxides, etc.

So, reckon it's worth wearing one of these then?

And finally...

As seen on the A12, few hundred meters from 88 Poppleton Rd.