“And you, having been dead in your the trespasses and sins, in which you once walked according to the fashion of this world, according to the ruler of the authority of the air, the spirit which now works in the sons of disobedience.”
“The prince of the power of the air,” this is the term that Paul uses to refer to Satan in this context. When combined with Paul’s reference to him as “the god of this world” (2 Corinthians 4:4) and Jesus’ reference to Satan as the “ruler of this world” (John 14:30), some have developed a theology that suggests that Satan is some sort of legitimate force that reigns in sections of this earth or peoples of this earth where the Gospel has not yet gone.
First of all, we should make clear that even in light of these references, Satan is at best a usurper, seeking for himself that which is not his just as Cain sought the blessings of his brother’s sacrifice. Satan also has no power apart from that which God permits him and thus God sets the boundaries and the length of the leash upon which the roaring lion is tethered. The Christian must be prepared for battle against him but should never fear him.
With that in mind, there is a theology that seems to rise to the surface periodically that is unhelpful at best and superstitious at worst. It suggests that until an evangelist takes the Gospel to a given location, Satan has dominion there. Upon what can that be based? God is omnipresent, is he not? While the Gospel has not been taken or received in a given location as of yet, that does not mean that such a locale is under the dominion of the devil. It simply means that Christians yet have work to do.
So, why then do Paul and Jesus use language such as this? Certainly this is giving the devil more than his due. To begin with, the language of satan being the god of or the ruler of this world is meant to set up a contrast. Christians become citizens of heaven whereas the wicked are only ever seen as those who dwell in the earth (you see this contrast play out prominently in the book of Revelation). Thus, those of earth worship the things of wickedness and the fall, hence they turn to their god and ruler, who is none other than the devil himself. It is not a popular thing to say, but it can still be fairly said that unless you worship the God of heaven, you are worshiping the devil.
As to the language that we find here, we should see Paul as making a distinction between the air — ἀήρ (aer) in the Greek — and the wind — πνεῦμα (pneuma) in the Greek. Much could be said here about the uses of each word, but let it suffice to say that the Bible presents the former as being more or less inert and not affecting anything whereas the latter is seen as life-giving. Never once do we see air performing this function, it is just there. If the devil has any power, it is over nothing of eternal consequence and it will fade like the grass in the summer heat. The Spirit, in contrast, is not like air, but like the wind, and goes where he chooses.