Free for riders: an 11-page guide to riding in bad air.

What is inside:

• What the AQI number actually means when you are on a bike
• A 60-second check before you head out, with the right app for your country
• The worst times of day, and the bad-season calendar
• 8 ways to breathe less of the traffic around you
• What masks really stop, and what they do not

Want live readings for your own city? Check the air where you ride.