Air currently does not have an "offline mode." The product must be connected to the internet to upload, collaborate, and share visual content.
This is a feature we're working on building to provide a seamless online / offline experience for all of our users.
If you're in an area without Wifi, consider downloading the Air mobile app for iOS or Android! It has all of the same functionality as the web app, plus you can take images and videos directly from your workspace to reduce clutter in your camera roll.