In Revelation 9:2, 'the sun and the air' here signify the light of truth, because 'the sun' signifies love, and the light divine truth. This is why when it says 'the sun and air were darkened,' it signifies divine truth becoming thick darkness. This darkening coming from 'the smoke of the pit' -- meaning that it was caused by falsities accompanying lust.

(Referencat: Apocalypse Explained 9 [2]; Apocalypse Revealed 423)

1859. That 'the sun went down' means the final period when the close came is clear from what has been stated above at verse 12 about the sun going down and about what that means, namely the final period of the Church.