Unlike HEPA air cleaners, shown at bottom, electrostatic precipitator air purifiers impart an electrical charge to the air,
creating charged molecules known as ions, which are supposed to cling to airborne particles. Electrostatic precipitators add
an oppositely charged collection plate or filter designed to attract the particles. Ozone is produced as a byproduct, which
then exits the machine and flows into the room air.
Ozone is created as high voltage converts oxygen to ozone. All electrostatic precipitators can create ozone, though some emit
more than others. Some people mistake ozone's sweet smell for a sign of cleaner air.
Illustrations by Trevor Johnston
Inside a HEPA air cleaner
Models with a high-efficiency particulate air (HEPA) filter are most common. Typically, a fan pulls air through a foam pre-filter
designed to remove some larger particles. The air is then forced through the pleated HEPA filter, which is designed to trap
most particles. The air might then pass through a carbon filter to remove odors. Sometimes the carbon filter will take the
place of the pre-filter.
Inside an ozone generator
Room air passes through a high-voltage plate, where some oxygen molecules are ionized. The ions combine with oxygen to form
ozone. The size of the generating plate and the amount of electrical current will affect the amount of ozone produced. Generally,
ozone generators emit high levels of ozone, so they are not meant for routine air cleaning. They should be used only by professionals
in unoccupied areas after serious contamination has occurred in the home, say from a fire or a flood.
