I have a little gadget on my kitchen shelf. It measures levels of a particle known as PM2.5 - the tiny, invisible, sooty bits of combustion that are key culprits in the air pollution health crisis.

Produced by diesel and petrol fumes, log burners and even conventional ovens, PM2.5s are small enough to make it deep into the lungs and from there into the bloodstream. They’ve been linked to diseases ranging from cancer to high blood pressure and, as the World Health Organisation (WHO) puts it, “increased mortality or morbidity”.

When I pop two slices of bread into the toaster for my six and four year old, the monitor goes bananas. The PM count in micrograms per cubic metre races up from 9 or 10...