can I use dragon naturally speaking with a mac air?

Yes, and no.

"Dragon Naturally Speaking" is a PC/Windows program, and will not function on the Mac OS*. The Mac version is called "Dragon Dictate". If you have, or buy Dragon Dictate for Mac, then yes you essentially have the Mac equivalent of Dragon Naturally Speaking.

* You could use Dragon Naturally Speaking under Windows on a Mac, provided you have Windows installed on your Mac. You would either use Bootcamp, or a VM app, such as Parallels or Fusion. At a minimum, you would need to purchase a full version of Windows 7, in order to install Windows on your Mac. IMHO, you would be better off considering Dragon Dictate.