Air apparent? (4)
I believe the answer is:
smog
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">air apparent?</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for smog that I've seen before include "Man-made atmospheric pollution" , "Fog polluted by smoke" , "Polluted haze" , "Pollutant haze" , "Pollutant fog" .)