Dogs lick air to better detect smells. Their sense of smell is very strong.  

Air licking can indicate nausea or motion sickness in dogs. If persistent, see a vet.

Nervous or stressed dogs may compulsively lick air. Try calming training.

Dental pain can cause excessive air licking. Have your dog's teeth examined.

Snorting & licking points to respiratory infection. Veterinary care needed.

Stomach issues like acid reflux can prompt air licking. Diet change may help.