My best theory is the Saharan dust one plus the Iberian smoke from wild fires. The two came together to show us these strange events. Today it is passing, though some are reporting a strong smell of burning, smoke or ash in the air.
The Bible does address these kind of things, speaking of the end of time. In Luke 21:25 Jesus said; "And there shall be signs in the sun, and in the moon, and in the stars; and upon the earth distress of nations, with perplexity; the sea and the waves roaring". When the apostle Peter was speaking on the Day of Pentecost he said this: ..."the sun turning black and the moon blood-red, before the Day of the Lord arrives, the Day tremendous and marvelous". I reckon that the physical events of yesterday show us two things. One, how the Bible predictions could easily come about, maybe even quite soon, and two that people do think deep and even spiritual thoughts when they see something like this happening.
Taking the Bible at its word, though, its biggest forecast is that one day Jesus Christ will come again. Our responsibility is to be ready for that day which, if yesterday felt "apocalyptic", will prove to have been as nothing compared to the real thing. The events of Monday certainly got us all looking upwards and Christian believers may have recalled the words of Jesus again "When these things begin to take place, stand up and lift up your heads, because your redemption is drawing near." (Lu 21:28)
