This Volatile Air farming guide will show you the places I use for farming 
Volatile Air. There were no major changes to Volatile drop rates in Cataclysm zones, so this guide can be used for Classic and Retail WoW.
Volatile Air
Vortex Pinnacle - Uldum
This farming place is for Retail WoW players only. If you play Classic, scroll down a bit for the other farming places. But, for retail players, this is the best farming place. They can ignore the rest of the guide. (assuming you have a high-level character)
Vortex Pinnacle is the best place to farm Volatile Air. You can find the entrance high in the air in the southeastern corner of Uldum.
Vortex Pinnacle entrance
First, you must set the instance difficulty to normal (right-click your portrait). You can't farm in heroic mode because you can't reset the instance after you kill the first boss.
Kill everything until the second boss, Altairus, then just simply jump down; you won't die; it will teleport you to the start of the instance. Go outside and reset the instance by right-clicking over your portrait, then click the "Reset all instance" button. This restarts the whole instance and all mobs will be back. You can only do 10 instance runs in an hour, which means sometimes you might have to wait a bit.
Vortex Pinnacle
Uldum
If you are too low level to solo Vortex Pinnacle, you can farm Scion of Al'Akir. There are a lot of them at Uldum, and they respawn very quickly.
The drop rate is around 12%, so don't expect one to drop for every other kill.
If you are an Engineer, you can farm Volatile Air with 
Electrostatic Condenser, but only if you have a gathering profession.
IMPORTANT! If you have a max-level character in Retail WoW, you will see the patch 8.3 version of Uldum. You can talk to Zidormi to switch between the new and old low-level phase of Uldum. (if you open the map, she will be marked with a white text bubble at Ramkahen)
Contact me if you have other great farming spots!