Runners are being encouraged to do their bit for clean air on Saturday as part of the third annual Running Up For Air event.
To raise awareness about air pollution, runners take part by logging ascent on a run between one and 24 hours long. It could be over hills, on a ski slope or even up stairs.
The Patagonia-supported event helps raise funds for 18 environmental groups which are campaigning for better air quality. The original event was created by US ultra runner Jared Campbell in 2012 and has since gained traction in Europe.
You can sign up by joining the more than 119,000 runners on the Strava challenge and optionally creating a fund-raising page. Special events such as this one in Bristol are being set up or you can take part solo.
Pic: Olly Bowman