Gene Fuller wrote:
Ionization threshold has nothing to do with "voltage". It has everything
to do with field strength.

Of course, static field strength implies energy which is
proportional to volts squared. Here's a quote from:

http://www.ce-mag.com/archive/1999/novdec/mrstatic.html

"A corona discharge is also called a silent discharge. It
may be maintained as long as the breakdown *field strength*
is exceeded in some region—that is, as long as the *voltage*
of the electrode or the *charge density* of the charged
insulator is high enough."

Just before the field strength is high enough to cause
ionization, the voltage between the electrodes can be
measured. I don't see how ionization could occur at
zero volts which you seem to imply is a possibility.
--
73, Cecil, http://www.qsl.net/w5dxp