A.T. Robertson Commentary Revelation 9:2

"And he opened the pit of the abyss; and there went up 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." — Revelation 9:2 (ASV)

Opened (ηνοιξεν). First aorist active indicative of ανοιγνυμ. With the "key" (κλεις).

As the smoke of a great furnace (ως καπνος καμινου μεγαλης). The plague of demonic locusts is here turned loose. Καμινος is old word for a smelting-furnace, already in 1:15.

Were darkened (εσκοτωθη). First aorist passive indicative of σκοτοω, old causative verb from σκοτος, in N.T. only here, 16:10; Ephesians 4:18.

By reason of (εκ). "Out of," as a result of (8:13).