As of this post, only a beta version of Adobe AIR is currently available. You can download it from here.
After the .bin file has been downloaded to your desktop, right-click on it and select Properties. Then select the Permissions tab, tick “Allow executing file as program” and click Close.
Open Terminal (Applications -> Accessories -> Terminal), type the following commands and press Enter. (Remember to change the text in red according to the name of the file you downloaded.)
The installation will now begin. Follow the instructions on your screen to install Adode AIR.