The most common and most likely answer to this crossword clue is the 9 letter word OXYGENATE
I've seen this crossword clue in The Times
O
X
Y
G
E
N
A
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E
More clues leading to the result OXYGENATE
Buddy explains!

The straight part
We know that "Enrich air, perhaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case enrich air, perhaps = oxygenate.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 OXYGENATE mean?
OXYGENATE verb- To treat or infuse with oxygen
- To give (a patient) oxygen therapy.