"Step back"

Traffic is queuing at the lights. Engines idle, then accelerate away. This is where exhaust pollution, nitrogen dioxide and ultrafine particles, is at its thickest.

You just can't see it.

Part one - where you stand

Waiting right at the kerb puts you in the densest part of the cloud. It's where most of us stand: toes on the kerb, watching for the green man.

Now take a step or two back.

Concentrations fall fastest in the first couple of metres, so standing just two metres from the kerb cuts what you breathe by roughly a quarter.

The back of the pavement is better still...

Exhaust pipes sit closer to buggy height. A child at the kerb breathes a more concentrated dose than the adult pushing them, and their lungs are still developing.

The same step back works doubly so here.

Stand back from the kerb, and keep the buggy back with you.

Part two - what's driving through

But standing back only moves you within the cloud. The cloud itself comes from the queue. Every idling engine feeds it, right where people stand waiting.

Switching off while you wait cuts the plume at exactly the place people breathe it. Many modern cars do this automatically. The rest have a button / key.

Electric vehicles remove the exhaust entirely, though tyres and brakes still shed particles, and every passing vehicle stirs road dust and residue from petrol and diesel traffic back into the air.

Fewer, slower vehicles beat cleaner vehicles. But cleaner helps, and it helps most at the kerb.

Part three - the bigger picture

This gradient runs along every busy road, all day. Pedestrians can step back from it. Drivers can shrink it. Planners can design to reduce its impact, with setbacks, barriers and space between traffic and people.

And bear in mind that, in England, most car trips are under five miles; consider avoiding short drives in built-up areas.