Upon the air (επ τον αερα). All men breathe the air and this is worse than the smiting of the earth (verse Revelation 16:2), the sea (Revelation 16:3), the fresh waters (Revelation 16:4), the sun (Revelation 16:8).

A great voice (φωνη μεγαλη). The voice of God as in Revelation 16:1.

It is done (Γεγονεν). Perfect active indicative of γινομα. Like Γεγοναν in Revelation 21:6. The whole series of plagues is now complete.