Brake dust a little recognised cause of air pollution

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Words: NZ Autocar
17 Sep 2020

It is becoming increasingly apparent that exhaust fumes from diesel and petrol powered vehicles are not the only cause of transport-related air pollution - brake dust may be as harmful as diesel emissions on immune cells.

Air pollution is known to cause health issues that kill up to nine million people annually. Included are respiratory and heart problems, dementia and certain cancers.

But exhaust fumes are not the only cause of foul air, with a bit over one-half of roadside traffic pollution comprising non-exhaust particles. One fifth of those come from brake dust, and these particles are evidently just as damaging to health as exhaust fumes. Much of the remainder comes from road components as they are driven over and degrade, and from tyres themselves.

Brake dust is composed primarily of iron particles, the result of pads rubbing on discs. These particles can trigger an inflammatory reaction in lung cells called macrophages, just as diesel particles do.

Moreover, brake dust prevents the immune cells from destroying certain bacteria, some of which are responsible for pneumonia. Therefore, pollution from brake dust might be contributing to the high numbers of chest infections and throat irritation that afflict people living in urban areas.

Traffic pollution particles contain thousands of materials, including carbon, hydrocarbons and bacterial toxins. Brake dust is highly metallic, containing iron, copper, titanium and magnesium, all of which can harm human cells.

When these metals are removed, the macrophages go about destroying bacteria but do not ramp up their inflammatory response, after exposure to both brake dust and diesel fumes. The latter contain far fewer metallic ions than brake dust, suggesting something else is triggering the response.

While reductions in exhaust emissions are important for public health, it would seem the auto industry needs to be concentrating on reducing brake dust as well. Designing technologies that are resistant to friction and wear may be important in reducing these harmful pollutants.

And that’s just what a Bosch subsidiary is doing, a new disc reducing dust production by up to 90 per cent. The cast iron disc ring is heated, rust treated and then given a tungsten-carbide coating. Called the iDisc it is more expensive than a cast iron unit, but nothing like as expensive as a carbon ceramic disc.

Given the morbidity caused by air pollution, anything that can limit the industry-wide production of brake dust should be welcomed.

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