Amount of charge spherical conductor can hold in air

[jh12]

I'm a little thrown off by this because we there is no voltage value given...
And how does the air play into the problem? I just something to help me get started:

What is the maximum amount of charge that a spherical conductor of radius 5.0 cm can hold in air?

 

[hage567]

http://en.wikipedia.org/wiki/Electrical_breakdown

The "Mechanism" section should answer your question about why the air is important.