Literally "in the air" means something suspended in the air. And the word "up" is usually used with it. For example, "we saw the plane flying high up in the air". But as an idiom, it means, in circulation, in people's thoughts. For example, "There's a rumor in the air that they're closing". "Christmas is in the air". " Though speakest, but, thy words are in the air". On air, or on the air means "broadcasting or being broadcast". For example, "The program will be on air at 3:00 PM:. "He changed his on-air name".

in the air:means sths is up in the air on the air: TV or radio is in recording

In the air= you are literally in the air meaning you "jumped in the air" or it could refer to flying in an airplane On the air=usually means you are on the radio "Hi this is 96.5 you're on the air with us" or on television, but usually on the radio

- 'In the air' can be used to talk about the outside air: 'She threw the ball high up in the air'. 'The troops fired blanks in the air.' 'To go for a walk in the open air.' However, it can also be used as an idiom to mean 'felt by a number of people to exist or to be happening': 'The lights were low and romance was in the air'. 'Her laughter soon dissipated the tension in the air.' 'There was a smell of burning in the air.' - on / off (the) air (idiom) = broadcasting or not broadcasting on television or radio: 'We will be back on air tomorrow morning at 7.'

in the air 在半空中 on the air 在空气中