Currently, they are used to generate high voltage for ion air
purifiers (ozone), that are supposed to make the air safer to breathe.

Well, there's a distinction to be made between "negative ion
generators" and "ozonators". The former tend to operate at
significantly lower voltages, and aren't intended to create ozone (O3)
although they may produce a small amount as a side effect. Their
primary output is negative ions, which some people feel make the air
more pleasant to breathe, and which definitely have the effect of
causing pollutant particles in the air to precipitate out onto filters
and onto every nearby surface.

I used to run a negative-ion generator in a commercial office space
located right under the Los Angeles Airport approach pattern. Lots of
stinky jet-fuel fumes and soot in the air outside. It definitely made
the air in the office more breathable. It also made a horrendous mess
of the walls and ceiling... after a month of operation I could see a
"shadow" on the wall if I moved a calendar or poster, due to all of
the soot and gunk which had precipitated out of the air. I understand
that after I left the company, they had to repaint the office to get
rid of the stained appearance.

Ozone generators are another matter entirely... higher voltage, more
corona effect (or, they use a high-intensity shortwave UV lamp to
create a similar effect by different means). I hate these things...
can't stay in a room with one for more than a couple of minutes before
my eyes start to burn and my lungs to ache. Why anyone would wish to
generate a free-radical-producing government-listed airborne pollutant
in their living space is beyond me!

Those piezeotransformer gadgets sound pretty neat, although I haven't
played with one myself.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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