Using the Air tab, you can give your model atmosphere, wind and gravity.
The Air pop-up allows you to add atmospheric effects to your model, such as fog or mist.
The Refraction index pop-up and numeric field lets you set a global index of refraction for your model. For example, you can set this to water for an under sea setting. Then you could generate a fountain of air bubbles rising to the surface. Remember, a refraction setting makes no difference until the light in your model encounters a boundary of change in the refraction index, like from water to air.
To add an atmosphere to your model, hold down the Air button, select New, to create your own effect, or select an effect from the pop-up list.
Once you select an effect, its editing dialog will appear. You can use the default settings, or edit them using the Copy From field.