One of the tiny, poisonous particles pumped out by vehicle exhausts is called magnetite. UK scientists have found it in the brain tissue of 37 people, and raised concerns about whether air pollution is contributing to causing Alzheimer’s disease.

We’ve known for a while that air pollution can trigger heart attacks and strokes, as well as worsen lung conditions like asthma. But the suggestion that it could also be linked to degenerative brain diseases is new, and deeply disturbing.

Yet we report today that legal air pollution limits meant to protect public health are being breached on 14 busy streets across Scotland. This is the sixth year running that the limits, which came into force in 2010, have been exceeded - and the problem doesn’t seem to be getting much better.

The number of air pollution zones – euphemistically known as air quality management areas – designated by local authorities in Scotland has increased from 33 to 38. Yet councils are squeezed for money, and can only do a certain amount on their own.

Neither councils nor the Scottish Government have much control over the multinational car manufacturers who flagrantly fiddled the tests designed to limit pollution from diesel engines. They also don’t have much say on clean engine standards or fuel taxes.

But there are a raft of key things they can do to try and limit excessive car use. They can encourage walking and cycling for short journeys, boost low-polluting public transport and introduce restrictions on high-polluting vehicles.

The Scottish Government has promised new “low emission zones” to cut pollution by 2018. But unless it also gives councils the money to help set up such zones, none are likely to commit to implementing them in the run-up to the local elections in May.

Elsewhere others are being more ambitious. In Seville pollution has been halved by an 80-kilometre network of cycle lanes, while in Paris the mayor has plans to half the number of polluting cars. London’s mayor, Sadiq Khan, wants to charge polluting motorists £10 a day from October 2017.

Scottish ministers claim to be leading the world on combating climate pollution. But if they fail to tackle the pollution on our streets that is killing more than 2,500 people a year, it’s hard to see how they could claim any kind of green crown. Or, indeed, how they could maintain their wider political credibility.