It emits ozone. This occurs when negative ions electrically charge particles suspended in the air. While ozone can act against microorganisms such as viruses, it also irritates the lungs. When we think of air filters and ionic air purifiers, many people will remember the infamous Sharper Image Ionic Breeze, an ionized air purifier with an electrostatic precipitator that, according to Consumer Reports, produced high levels of ozone, a by-product created by the ionization process.
Ozone, according to the EPA, is a dangerous by-product that can harm the health of exposed people, such as chest pain, cough, shortness of breath and throat irritation. Ozone is very harmful, however, you can install an ionizer and it complies with the UL 2998 standard, which basically states that this product does not produce ozone. I purchased and installed IWAVE ionizer systems by a professional for my top and bottom air conditioning systems. GPS is marketing a Neddlepoint bipolar ionizer for air conditioning applications that claims to have high levels of negative and positive ions, but zero ozone emissions. However, to prevent my roommate from second-hand and third-hand smoking, I now plan to keep my ionizer on only for 30-40 minutes when no one is in the room and then turn it off before anyone comes in.
As more information about the dangers of air ionizers is released and presented to the public, the more informed consumers will be before purchasing an air purifier and are likely to be aware of and avoid these potentially hazardous ionizing air systems. Air ionizers are designed to help provide cleaner air and they do this by using ionized particles. Since conflicting data related to the ionizer persist, I usually keep the ionizer option turned off. Air purifiers with ionizers are generally safe because ionizers don't have enough energy to be harmful to health.
These ionizers turn on for 8 hours every day and I have a Therapure TPP300D with UV+ ionizer that is on for 8 hours in my living room.