"The previous bowls have been poured out upon the earth, the sea, the rivers and fountains, the sun, the throne of the beast, and the great river Euphrates. This, the last and greatest, is poured into the air; and immediately there is heard a voice out of the temple in heaven, proclaiming, "It is done!" What, then, is symbolized by the plague poured into the air? Of what is the "air" the emblem? In the Revelation the whole of nature is used as a great complex parable or symbol. What does the atmosphere especially signify? And the answer is not difficult. If earth, sea, rivers, fountains, the sun, a throne, etc., denote manifest spiritual realities, the air obviously would symbolize an invisible spiritual realm. And here we are helped by sundry hints of scripture usage."
Much more in the text:
"The air is the realm of the firmament, or a dimension of heaven; therefore the air signifies the spiritual atmosphere, either positive or negative, where men walk. All realms of life have their "atmosphere" -- the air. If you go to a bar there is an atmosphere there. If you go to a brothel there is an atmosphere there. If you go to a rock concert there is an atmosphere there. If you go to a Baptist church service there is an atmosphere there. If you go to a Pentecostal church service there is an atmosphere there. The atmosphere at a Catholic mass is altogether different from the atmosphere at a Charismatic meeting. Every realm has its atmosphere! When you enter the presence of a son of God who knows the truth as it is in Jesus, who walks in the wisdom of the mind of Christ, who expresses the unconditional love of God, and dwells in the glory of God -- there is a clear, powerful, victorious, confident, peaceful, transforming atmosphere there!"