Diesel, not just dust, has helped create this smog
Saharan winds may account for the dirt on cars, but the real problem is soaring levels of particulates in European air - The Guardian, 02.04.2014
03 April, 2014
No one doubts that the Saharan dust in the smog affecting parts of the UK is to blame for the layer of grime now sitting on cars but experts agree that the more dangerous element for people's health is the increasingly noxious pollution belching out of our vehicles and industrial plants.
Air pollution from vehicles, factories and homes is now so bad, regularly, in Britain that when it is exacerbated by a storm in the Sahara 2,500 miles away, or by high pressure over northern Europe, it can leave millions gasping, their skin itching and eyes watering.
When, as has happened this week, all three factors coincide, the outcome is a "perfect storm" for air pollution, says Helen Dacre, a meteorologist at Reading University.
First, emissions from British traffic and industry have steadily built up in the air. Then gentle easterly winds have brought more pollution from the industrial centres of continental Europe. To make matters worse the dust that has blown in from the Sahara has been whipped up by a storm that produced gale force winds in north Africa.
The pollution seen in the milky white air that has blotted out the sun and shrouded half of Britain for much of the past few days, is mostly made up of tiny particulates, such as nitrates and sulphates, mixed with fine desert dust. The particulates come from partially complete combustion processes, but diesel engines are a big culprit, and wear and tear from brake pads and tyres, as well as construction sites, all add to the problem.
Saharan dust is blown in all directions. Much is dumped in the seas. But several times a year strong southerly winds bring dust clouds as far north as Britain, mostly during spells of dry weather in Europe, which stops the dust being washed out by rain along the way.
The size of particulates is directly linked to their potential to cause health problems. The smallest particulates, those less than 2.5 micrometres, called PM2.5s, are the most dangerous because they penetrate deep inside lungs. Long-term exposure to particles is linked to higher levels of fatal heart and lung disease, including lung cancer.
According to the Committee on the Medical Effects of Air Pollutants, a rise in the PM2.5 level of 10 micrograms per cubic metre leads to a 6% increase in overall death rates.
Today's pollution mix is different from that which plagued Britain 70 years ago. The historic culprit was coal burnt in homes and factories; you could smell it and see it in the tiny bits of carbon or unburned fuel that collected on clothes.
But the pollution now is colourless, odourless and tasteless, and mainly comes in particles so small they can pass through face masks. Traffic, especially diesel engines, is the predominate pollution source in cities.
One reason for the increased pollution is that there are now far more diesel cars. Numbers have increased across Europe by 35% since 1990 and, says the Society of Motor Manufacturers, more than 50% of all cars registered in Britain are now diesel, up from 23% in 2002. One reason for this is that cities and governments give tax incentives for diesels.
What worries medical researchers at Kings college, London, is that the air is now full of nano-sized pollution particles that interact with gaseous co-pollutants and get deep into the body. The more that air pollution from traffic is researched, the more dangerous it appears to be. Last year the World Health Organisation accepted that air pollution could cause cancers. Last month it doubled its estimate of how many people die yearly from this cause. More than seven million deaths, or one in eight of all deaths, are linked to it.
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