Stephen Rees's blog

BBC on Harvard School of Public Health Report

Breathing in air pollution from traffic fumes can raise the risk of potentially deadly blood clots, a US study says.

Exposure to small particulates – tiny chemicals caused by burning fossil fuels – is known to increase the chances of heart disease and stroke.

But the Harvard School of Public Health found it also affected development of deep vein thrombosis – blood clots in the legs – in a study of 2,000 people.

Particulates are nasty little things, but their chemistry is horribly complicated and they are difficult to measure and quantify because they are so small. A lot of attention is paid to diesel emissions because they contain small particulates: in fact the number of very small particles has been increasing as the technology to reduce the total weight of emitted particles has been improving. And the smaller the particle the further it can penetrate into the lung. So the links to asthma, lung and heart disease are fairly clear.

What this research does is provide an understanding of how particulates have even wider impacts than we used to think. And these particles may not be directly emitted, but form in the chemical soup that the air we breathe in our car oriented urban areas has become. There are chemical reactions that lead to the creation of more particles as the various pollutants interact with the nitrogen, oxygen and hydrocarbons that are in the air naturally. I have long suspected that more attention was being paid to trucks and buses, because that way car drivers can point the finger elesewhere. In this region, where cars have to pass regular emissions testing (but not, of course basic roadworthiness or safety checks) people believe their cars are clean becuase they have a certificate that tells them so. And every time a heavily loaded bus accelerates away from a stop there is the tell tale plume of smoke. So obviously that convinces the car drivers that air pollution is not their fault.

In truth, of course, the huge volume of vehicles means that the impact of cars as a whole is much greater than the relatively small number of buses and trucks. And while those cars  generally have passed Air Care, they are far from zero emission, and the total volume of emissions is very significant.

What is also not said in the BBC piece, but I think may also be worth looking at is the fact that air quality inside vehicles is usually much worse than the air in general. And many people are inactive, since they are sitting in their vehicles for long periods. Taxi drivers should be concerned. But I would also like to see studies done in North America since the use of diesel cars is much greater in Italy (where this study was done) than it is here.