Wendy Zuckerman

And that is not how it used to be.

In fact, London used to burn so much coal that the air turned this gross, pukey colour.

When that happened, it was known as a pea super.

So time for a bit of history, and then we'll get back to Rosamund's story.

One of the worst events where smog took over London was known, appropriately, as the Great Smog of London.

If you're a fan of The Crown, you know what I'm talking about.

It happened in December 1952.

Here's a BBC doco about it.

The smog stuck around for five days and ended up killing thousands of people.

But they could do something about it.

And they did.

Events like this kicked governments in the butt to get rid of the smog.

In places like the UK and the US, where similar events happened, they started passing clean air acts to cap how much gunk power plants, homes, and cars could spew into the air.

And these laws, they made a big difference.

Car exhaust is safer than it used to be, and many power plants now have doobie whackers on them, like scrubbers, to keep some of the pollution out of the air.

So yeah, for London, no more pea soupers.

But over the years, scientists have come to realise that the invisible stuff that is still getting pumped into our air, it can do some dangerous things to our health.

One researcher told me it scares the shit out of her.

This pollution can break down into teeny tiny pieces about the same size as bacteria.

They float in the air and when you breathe them in,