Air!

Air! is an achievement/trophy in Metro Last Light Redux.

Overview
This achievement is obtained after using up 30 minutes worth of gas mask filters. On the surface and in areas filled with unbreathable/poisonous gases, Artyom needs to equip a gas mask to survive. Gas mask's filters have limited durability (they usually last for 5 minutes) and need to be replaced after prolonged usage. Using six full filters (6 * 5 minutes = 30 minutes) grants the player this achievement.

The player can see the remaining durability of their filter on Artyom's watches and the game will alert the player when the filter needs replacing. Note that filter's durability only decreases in areas where a gas mask is necessary.

This achievement isn't hard to get and will probably be obtained by most players without even counsciously trying to get it, as there are numerous levels which require going to the surface and the player will be using their gas mask for the majority of these levels.