Just before this BBC podcast gets underway, here's something you may not know.

My name's Linda Davies and I Commission Podcasts for BBC Sounds.

As you'd expect, at the BBC we make podcasts of the very highest quality featuring the most knowledgeable

experts and genuinely engaging voices. What you may not know is that the BBC

makes podcasts about all kinds of things like pop stars,

poltergeist, cricket, and conspiracy theories and that's just a few examples.

If you'd like to discover something a little bit unexpected, find your next podcast over at BBC Sounds.

Hello and welcome to more or less your guide to the numbers in the news and in the world around us.

I'm Kate Lamble.

On this show we always welcome your attempts to stump us with stup

with stup with stupendous statistics and you can get in touch

by tweeting us at BBC more or less or email your questions to more or less at

BBC.co. UK. That's where Adam Dawson sent us a stat he'd read which he thought sounded extraordinary.

92% of those in cities breathe unsafe air.

The figure originates from the World Health Organization who actually

say it's 92% of the total global population and 95% of those living in cities who are

breathing unsafe air. But whatever the exact percentage, it's initially really

unclear what they mean by unsafe. What are they even measuring here?

Gavin Shaddick is chair of data science and statistics at the University of Exeter in England.

Unsafe air in that case refers to levels of fine particulate matter,

which are very, very small particles in the air,

less than 2.5 microns in diameter, so small enough to go through our noses

...