Air transport is increasingly used to export fruit and vegetables to countries where they cannot be grown or are out of season.
Is there a synonym for "increasingly"? And, can I use "growingly"? (It is for IELTS exam.)
Growingly would not often be used here. We sometimes use "growingly" to modify adjectives
He is growingly unhappy with his position at work.
The most common word in your example would be "increasingly", or you could say "more and more". Using "increasingly" is more formal and adult.
Air transport is being used more and more to transport...