Something in the air

Dickens once described London as a city of soft, black drizzle and sooty flakes. Today, air quality is much improved, yet any jogger or cyclist taking deeper and more frequent breaths than nonexercisers can't help but ponder the effects of air pollution.

And rightly so, when the average adult inhales about 5trillion particles daily, many of which are droplets of sulphuric acid, nitric acid and black smoke generated by exhaust fumes. Wheezing in at 102 out of 215 in a global survey on cleanliness, London is dirtier than both Rome (98th) and Paris (84th).

Wheezy does it

Studies by the Department for the Environment, Food and Rural Affairs reveal that toxic air contributed to 20 to 40 per cent of deaths caused by last summer's heatwave in England and Wales.

Most harmful is diesel - breathing in an old doubledecker's fumes can damage your lungs. The discharge, composed mainly of carbon particles (thoracic particulates), has pollutants often less than one micron in size. These get into the lungs and lay in the alveoli - the lung sacs where oxygen transfers to the blood stream.

Halving your long-term exposure to these air poisons could decrease your life span by one to 11 months. And Government reports suggest that road transport, not factories, is responsible for 97 per cent of the carbon monoxide in the air.

But carbon particles aren't the only culprits. The other cause of high air pollution levels is ozone. Like carbon particles, it is a major factor in lung damage and also aggravates asthma conditions. Last year, because of higher temperatures and sunlight levels, Londoners saw the highest ozone levels since readings started in 1993.

So does this mean that the cardiovascular benefits of urban exercise are cancelled out by the impact of breathing in dirty air? A British Heart Foundation spokeswoman believes not.

'The benefits far outweigh air pollution,' she says. 'Heart problems are the biggest killers in Britain and cycling or doing other exercise for 30 minutes a day can slash the risk by half. And you can always wear a mask.'

Bill Chidley, chairman of the London Bicycle Messenger Association, suggests that as you are inflating and deflating your lungs vigorously when cycling, you flush from your system more harmful pollutants than you avoid by not exercising.

Fuming drivers

'Pollution is a problem,' he says, 'especially for car drivers. There is evidence proving that their intake is higher because they are lower to the ground. The taxi driver probably suffers more than the cycle messenger.'

Indeed, according to the Rough Guide To Cycling, motorists are exposed to three times as much pollution as cyclists. In gridlocked jams, air quality is often poorer inside the car because the air intake at the bonnet is at the same level as the exhaust.

Lucky for cyclists, then, that they don't get gridlocked.