Air pollution. “Pea souper” smog may be a thing of the past, but less visible pollution is still 

exacting a toll on the health of commuters and city dwellers. And it’s not just our lungs that 

are affected. A landmark European study published just last month found a link between 

invisible particles of soot and the risk of heart attack.

Frank Kelly is Professor of Environmental Health at King’s College London.

Kelly
It builds on a very large literature which indicates that there is an association between living 

in an area which has got higher air pollution and a major health outcome, which is heart 

attacks. So the study was done across five European countries, it ran for 12 years and it 

involved over 100,000 people.

Porter
And that increased risk was how much?

Kelly
That increased risk was relatively small, it was the order of between 5 and 10% but it’s still 

a risk and…

Porter
Heart attacks are common as well.

Kelly
… there’s 45,000 people die from heart attacks in the UK every year and if we can help that 

component of that sector by minimising the risk then I think everybody would be very 

grateful.

Porter
So a small increase but in a common thing?

Kelly
Yes, we all have to breathe.

Porter
Looking at the pollutants themselves, I mean with the advent of the catalytic converter of 

course petrol engines were cleaned up and you can’t smell the fumes like you used to be 

able to but there’s a new danger emerged?

Kelly
Yes, Europeans have got a great love for the diesel engine because we thought it was a 

more efficient than the petrol engine, we could get more miles to the gallon. That’s not really

 true anymore and we’re left really with the problem of diesel being much more of a polluting

 fuel than petrol is. A typical figure that’s usually used is that you’ll get 20 times more 

particles from a diesel exhaust engine than you will from a petrol engine.

Porter
And explain what these particles are.

Kelly
So these are small carbon particles, so small you can’t see them. And to try and put that 

into context – a human hair, which you can just see, is 60 micrometres in diameter, the 

largest of these particles that can get into your lung are only 10 but the majority of them are 

much, much smaller than that. So they’re invisible to the naked eye but they’re produced in 

very large quantities from all our transport systems and in urban environments.

Porter
Are modern cars with all of the latest emissions are they still producing these particles?

Kelly
Modern cars – they have become cleaner but they haven’t become clean enough. And 

what has unfortunately has become apparent, just in the last 12 months is, is that these 

fantastic exhaust systems work beautifully in the factory whenever the car is running to a 

very set cycle but the technology, it turns out, doesn’t work that well in real life. So if you 

have a vehicle on a London road, which is running at maybe 12 or 13 miles an hour 

because of congestion, it never gets up to the right temperature to effectively work properly. 

So we’re getting a lot more pollution from a vehicle which is meant to be very clean.

Porter
And how are these particles actually harming us?

Kelly
The difference about these modern vehicle exhaust particles are that they’re very small, so 

they’re actually getting to parts of our bodies, deep parts of our lung, which particles have 

never been able to get to before because we’ve always had the larger ones associated with 

burning wood and coal. But these modern diesel associated particles are so small that 

some of them can actually get across our lung into our circulation. Now that’s never 

happened to the human lung before but if you get this happening day in, month in, year in 

over decades then clearly it can build up to a big problem.

Porter
This new study looked at a link between pollution and heart attack, do we think that these 

small particles getting into the bloodstream are affecting the heart that way, is that how…?

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part 2

Kelly
There are two main theories. One is that yes they are transferring across from the lung into 

the circulation and affecting blood vessels and the heart directly. The other theory is that it’s 

not the particles themselves but it’s what they carry on their surface, so they carry these 

complex chemicals of metals and organic compounds which you get from combustion and

 then when they get into the deep lung they leach off and they move across the cells into the circulation – that’s the chemicals. And it doesn’t really matter, the bottom line is that they’re getting across whether they’re on the particle’s surface or not.

Porter
What happens to these particles once they come out the back of an exhaust pipe, are they 

dispersed like gases would be?

Kelly
Absolutely. So immediately beside a busy road there’ll be a high concentration of them and

if you happen to be moving along that pavement or whatever you’ll be breathing them in

 fresh. But very quickly they do move up into the air and depending on the weather 

conditions they’ll be mixed with older particles and they may, if there’s not high buildings on 

the road, they may be cleared across out of the city very quickly.

Porter
What about people who are cycling and pedestrians who are commuting, the children who 

are walking to school, presumably the more vigorous the activity that you’re doing in this 

polluted air the more likely you are to draw these particles in?

Kelly
Absolutely, so everything I’ve been talking about so far is to do with concentration of 

particles in the air. Obviously someone who’s cycling they’re breathing much harder, or if 

they’re running they’re breathing much harder, if it’s a child playing they’re breathing much 

deeper and longer. So it’s that volume of air and the concentration of pollution in the air 

which gives you the ultimate figure which we all need to pay attention to.

Porter
What about filtering these particles out? First of all let’s talk about the cyclist then – we see 

lots of cyclists in London wearing masks, do any masks work?

Kelly
Certainly the relatively cheap disposable masks they will not prevent the particles entering 

the lung because they are too small. So effectively if you’re going to stop those you would 

have to have something which basically stopped you being able to breathe. There are 

some higher end masks which have activated charcoal as part of their makeup and they will

trap some of the gases which we worry about – we haven’t talked about those, like nitrogen 

dioxide which also has health effects – though actually to stop these very small particles 

you have a big challenge on your hands.

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Porter
If it’s not practical to wear that sort of mask what would your advice to cyclists be?

Kelly
So unfortunately many of the major cycle routes are along our busiest roads and that’s where
the most pollution is. So there are now apps and maps available which will allow cyclists to
plot their route from A to B by maybe adding two or three minutes to their journey but just going
down some side roads, some back roads, through parks and they’ll have a much pleasanter
experience and they can drop their exposure level to this pollution considerably, I mean many fold.

Porter
And to put diesel cars in context, I mean we haven’t talked about buses and other – the heavy
goods vehicles, but look at the cars – a modern diesel car compared to the equivalent modern petrol car, how clean is petrol now?

Kelly
Very, very clean, the technology for the petrol car has really led to a much improved combustion
of the fuel and as a result some of the new Euro Six petrol engines are producing very, very small
amounts of particles and very, very small amounts of oxides and nitrogen in the gas. If you want
to drop pollution with the technology that’s available at the moment then a small engine petrol
vehicle is ideal.

Porter
Professor Frank Kelly. And don’t think you are protected because you are sitting in a car – most
modern automotive filters are not fine enough to remove diesel particulates, and you are breathing
the same air as the cyclists and pedestrians.

Diesels can be run perfectly safely on vegetable oil, which they were designed for in the first place.