Michael Mosley

Focus-Science and Technology - - CONTENTS -

Air­borne pol­lu­tion: the silent killer.

Much of my work­ing life is spent in Lon­don and I cy­cle ev­ery­where. It’s a fast, con­ve­nient way to get around, but I do worry about the air I’m breath­ing. When it comes to air pol­lu­tion, Lon­don comes out badly. So what is the best way to get around a busy city if you want to min­imise your ex­po­sure? Walk­ing, driv­ing, cy­cling, or the Un­der­ground?

The story around air pol­lu­tion is con­fus­ing. Six years ago I bought a diesel car. I’d read that diesel pro­duces less car­bon diox­ide per mile than petrol, so I thought I was do­ing my bit for the en­vi­ron­ment. It turns out that I’ve been con­tribut­ing to the nearly 40,000 pre­ma­ture deaths that hap­pen ev­ery year in the UK as a re­sult of air pol­lu­tion. This is more than 20 times the num­ber of peo­ple that die in road ac­ci­dents and is only ex­ceeded by the 80,000 who die ev­ery year as a re­sult of smok­ing.

The trou­ble with diesel is that it pro­duces a lot of ni­trous ox­ide, which ir­ri­tates the lungs, and ozone, which is also bad for the lungs. Ozone is formed when ni­trous ox­ides and other volatile or­ganic com­pounds re­act with sun­light, so lev­els can get spec­tac­u­larly high dur­ing the sum­mer.

As well as these gases, diesel en­gines pro­duce lots of tiny specks of par­tic­u­late mat­ter (PM). These specks are so small that they can pen­e­trate deep into your lungs, car­ry­ing with them a host of un­burnt com­bus­tion com­po­nents. These in turn trig­ger re­ac­tions that dam­age your blood ves­sel walls, con­tribut­ing to heart dis­ease, type 2 di­a­betes and Alzheimer’s.

So when I’m cy­cling around Lon­don I’m in­hal­ing all this stuff, which has to be bad for me. But how bad is bad? To find out I took to the streets of Lon­don wear­ing a pol­lu­tion mon­i­tor­ing de­vice. I walked from the Strand to Mar­ble Arch, a dis­tance of about five kilo­me­tres (three miles). Then I cy­cled back, but tak­ing qui­eter back streets.

Fi­nally, I jumped into the back of a taxi and went an­other five kilo­me­tres, this time through rel­a­tively heavy traf­fic.

So what hap­pened? Well, when I walked to Mar­ble Arch the route I took was con­gested with buses and taxis, and the de­vice I was wear­ing recorded an im­pres­sive rise in the lev­els of pol­lu­tants in the air I was breath­ing. When I re­turned down the back streets on my bike I was re­as­sured to see that the lev­els dropped off re­ally dra­mat­i­cally.

But the high­est spikes, sug­gest­ing the worst lev­els of pol­lu­tion, were when I was sit­ting in the back of the taxi. That’s be­cause if you are sit­ting in a car in traf­fic then the air in­let of your ve­hi­cle is go­ing to be right be­hind the ex­haust pipe of the ve­hi­cles in front.

You can turn off the air in­lets and close the win­dows, which will make some difference, but the fact is that when you are stuck in traf­fic you are sit­ting in a gi­ant pool of in­vis­i­ble pol­lu­tion to which you are also con­tribut­ing.

I didn’t try trav­el­ling on the Lon­don Un­der­ground, but I sus­pect that if I had then the re­sults would have been even worse. A study last year by the Uni­ver­sity of Sur­rey found that peo­ple trav­el­ling by the Un­der­ground were breath­ing in far larger amounts of dam­ag­ing PMs than those who were trav­el­ling by bus or car. So I am de­lighted to say that cy­cling is not only in­cred­i­bly con­ve­nient but also one of the best ways of trav­el­ling around while avoid­ing air pol­lu­tion.

You could spend a lot of money on a so­phis­ti­cated mask with ac­tive char­coal fil­ters that will take out the gases, but you’ll still be breath­ing in tiny par­ti­cles. My best ad­vice is to do what I do now, and take the quiet back streets. It takes a lit­tle longer, but it makes me ap­pre­ci­ate what a won­der­ful city Lon­don is. De­spite the pol­lu­tion.


Michael Mosley is a sci­ence writer and broad­caster, who presents Trust Me, I’m A Doc­tor on BBC Two. His lat­est book is The Clever Guts Diet (£8.99, Short Books).

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