The temperature is 20°C. (Colloquial. By default this would be understood to be the air temperature) The air temperature is 20°C. (“Air temperature” refers to a certain meteorological measurement, so it’s more precise.) The temperature of the air in my attic can reach 140°F. The temperature of the air in the freezer never exceeds -3 °C. (General. Note “the” air)

Both phrases have the same meaning! It depends on how it is said in the conversation.

Both are correct and mean the same thing, but air temperature is the most common way of saying it.

Hello! In my opinion, using "air temperature" is a better way of saying it as this is the compound noun. To say "the temperature of the air" is a long and clumsy way of saying it although that would probably be the direct translation from another language. I hope this helps!