I made this Essence of Air farming guide to help out players who want to farm the essences instead of buying them from the Auction House.
Essence of Air
Killing Dust Stormer at Silithus is the only way to farm Essence of Air. The drop rate is only around 5% and mobs are spread apart, so it's not really an ideal farming location.
Unfortunately, the respawn rate is slow, so if you are killing the mobs too fast, you will have to wait for respawns.
IMPORTANT! If you are level 50+ and done the Argus questline, Silithus will be phased and these mobs will not be there. But, if you talk to Zidormi, she will allow you to switch between phased/low-level and Legion/high-level versions of the Silithus. (if you open the map, she will be marked with a white text bubble at northeast)