Ionizers utilize high voltage to add electrons to molecules and, in the case of air ionizers, the electrons are added to components of air, including oxygen. Negatively charged oxygen molecules are unstable and rapidly interact with other molecules with the reaction usually releasing oxygen. However, ionizers do not generate the amount ozone typical of ozone generators. Negatively charged ions may bind to and charged particles in the air or environment and help with neutralization or elimination. Help is the operative word as the magnitude of effect of ions on the environment is debated. Most allergens are positively charged so the concept is the negatively charged ions will bind to the allergen and in some way reduce the allergenicity. Electrical charge may reduce the viability of organic particles but the importance of this for respiratory disease, other than infections, is not clear. There is no debate about the negative effect of ozone (Title 21—Food and Drugs; Chapter I—Food and Drug Administration Department of Health and Human Services; Subchapter H—Medical Devices". US Food & Drug Administration (FDA) website. Retrieved 2006-08-30) with the FDA concluding there is no place for ozone in medical treatment. Ozone in very low concentrations provides a pleasing smell to some people and the smell is often described as clean. Therefore, ions can occur with multiple substances and ozone and ions are not identical although usually when negative ions are generated some ozone results. To my knowledge, there is no risk from exposure to negatively charged ions generated by household appliances.
In summary, you are correct that ozone and negative ions are not equivalent but ozone is formed by electron transfer to molecular oxygen in the gaseous phase. Negative ions may or may not have some benefit for allergic respiratory disease but the existence or magnitude of this benefit is debatable. Studies have been inconclusive to date. I would not recommend such devices for therapy at this time. Ozone has clearly detrimental health effects if the levels exceed 0.1 ppm as a daily average. To my knowledge, household appliances that generate negative ions are not a risk for patients with asthma.
I hope this information is of some help.
All my best.
Dennis K. Ledford, MD, FAAAAI