Written on the wind

Earth is pretty much uninhabitable because there's no oxygen left. Handful of people are holed up living in basements and underground tunnels. Luckily they are quite intelligent and have devices to produce precious air. Freshen up a bit, eat healthy and do normal stuff like read. With state-of-the-art oxygen kits they can explore the world, scavenge for food and supplies. Things get tricky and possible volatile when people meet other people and it's a guessing game are all the gun-toting strangers reliable and nice. It's a bit silly, Stefon Bristol's Breathe, but there are worse dystopian flicks out there.