The most common and most likely answer to this crossword clue is the 8 letter word EMERSION
I've seen this crossword clue in Financial Times
E
M
E
R
S
I
O
N
Buddy explains!

The straight part
We know that "coming up for air" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coming up for air = emersion.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EMERSION mean?
EMERSION noun- Emergence, especially from the water.
- The reappearance of a heavenly body after being eclipsed by another or by the sun's brightness.