The Air Mask allows you to breathe safely in areas filled with hazardous gas (and not just the kind from Kell Dragons). Kyle's mission to track down the nature of infrastructure supporting the dark trooper project will require him to visit a number of industrial sites, so if you encounter toxic fumes look around for an air mask. Shields don't do anything against that kind of damage, so also make sure you've got enough battery power to last you through the area.