{4} And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit.

(4) To this is added, the smoke of the hellish and infernal dark spirits, darkening all things in heaven and in earth. The spiritual darkness is the cause of all disorder and confusion: For the devil at a certain time sent these spirits into his kingdom, that he might at once and with one action overthrow all things and pervert if it were possible the elect themselves. By this darkness, all spiritual light, both active as of the sun and passive as of the air which is lightened by the sun, is taken away: and this is that which goes before the spirits: it follows of the spirits themselves.

Scofield Reference Notes

Margin smoke

Contra, Rev 21:24 Joel 2:10.

Revelation 9:2 Parallel Commentaries

Jesus Heals Two Gergesene Demoniacs.
(Gergesa, Now Called Khersa.) ^A Matt. VIII. 28-34; IX. 1; ^B Mark V. 1-21; ^C Luke VIII. 26-40. ^b 1 And they came to the other side of the sea [They left in the "even," an elastic expression. If they left in the middle of the afternoon and were driven forward by the storm, they would have reached the far shore several hours before dark], ^c 26 And they arrived at the country of the Gerasenes, which is over against Galilee. ^a 28 And when he was come into the country of the Gadarenes. ^c 27 And …
J. W. McGarvey—The Four-Fold Gospel

Thyatira
In the Epistle to Thyatira we have the reference to another and more intensified form of idolatry as developed and established in the days of Ahab, king of Israel; another who, like Balaam, "made Israel to sin" (1 Kings xvi. 30). Ahab was the first king who officially introduced and organised he most abominable form of heathen idolatry that the human mind ever conceived (1 Kings xvi. 33). See Revised Version, where the special significance of this abomination is conveyed and contained in the word …
E.W. Bullinger—Commentary on Revelation