Do you know which is the energy per mol required to ionize air? Once the air is ionized, does it recombine it´s charges so that after a while there is no ionized air at all? If this is the case, how long does it take for this to happen?
I'm not sure whether or not this is homework, but this might be most appropriately answered in the Chemistry forum. Dredging up some of my high school chemistry, the process for ionization requires you to first break the molecular bonds (the triple bonds of nitrogen, and double bonds of oxygen) and form free atoms. Then, you need to ionize them.
Now, assume you have 1 mol of 'air' (0.79 mol of N2 and 0.21 mol of O2), figure out how much energy you need to break the bonds: