airing vs mystery tour

airing

noun
  • A public expression of an opinion or discussion of a subject. 

  • The broadcast of a television or radio show. 

  • An exposure to warm or fresh air. 

mystery tour

noun
  • A short-duration outing by coach to a destination that is not revealed in advance 

How often have the words airing and mystery tour occurred in a corpus of books? (source: Google Ngram Viewer )