The discharges in the clouds are caused by electric potential between two spots being larger than approx 3200 volts per millimeter. That value is called air breakdown threshold (the value is for standard pressure and mixture), above that voltage air becomes a conductor. Hence the lightning, where a potential between spot in the air and ground must be millions of volts in order for air to conduct electricity all the way down to ground. The nice and fresh air is not due to ozone, which most people believe, but due to negative nitrogen or oxygen ions, e.g. constituents of the air that got an extra electron via the electric field caused by big voltage.
Technically you should be able to get this nice air by putting a tazer or something that sparks electricity right in front of a ventilator.