According to Paul's usage, in the simple physical sense. See Act 22:23; 1Co 9:26; 1Th 4:17; Rev 16:17. The air is regarded as the region of the demons' might.
The spirit
See on 1Co 2:12. The term designates the power over which Satan rules, on the side of its operation in men's hearts.
Now
With an implied reference to its former working in his readers. Compare once, Eph 2:3
Children of disobedience (υἱοῖς τῆς ἀπειθείας)
Compare Eph 5:6. A Hebraistic expression. Compare son of perdition, Joh 17:12; children of obedience, 1Pe 1:14; children of cursing, 2Pe 2:14. Rev., correctly, sons of disobedience: belonging to disobedience as sons to a parent.