Negative ionizers should not be confused as ozone generators, even though both devices are air cleaning machines.
A negative ion is an oxygen atom with an extra electron and is odourless. Whereas Ozone is an oxygen molecule consisting of three oxygen atoms and produces a smell at high concentrations.
Ionizers use electrostatic-ally charged plates to produce positively or negatively charged gas ions (for instance N2 or O2) that particulate matter sticks to in an effect similar to static electricity. On the other hand, ozone generators are optimized to attract an extra oxygen ion to an O2 molecule, using either a corona discharge tube or UV light.
The term "ozone generator" refers to an appliance purposely built to create ozone in large quantities. Our air purifiers that produce negative ions are not the same ozone generators - they do not produce ozone in large quantities in order to clean the air.
You can read more about it here.