How They Work
The Internet is replete with positive and negative reviews of these ionizers. The reality is that ionizers at least work in a limited capacity. The way that the ionizer works is that it uses negative ion generators to attract particulates from the air, creating air that is free of these particles. These particulates usually include dust, dander and other airborne substances that cause allergies and odor. Ionizers in refrigerators do this in a limited capacity in so far as these are in the refrigerated air.
Assessment
Assessing the usefulness of an air ionizer in a refrigerator ultimately depends on the model and its features. Some ionizers are basically useless because they have no fan to circulate the air through the system. The air needs to be circulated across the negative ionizer to change the charge of the particulates. Some ionizers simply trap dust and pollen with no real affect on the remaining air. Ionizers do not typically remove odor from the air though, so the reality is that those in refrigerators will have little to no effect.
Ozone
Negative ion generators that also produce small discrete amounts of ozone are more likely to have an effect on the air quality in the refrigerator. Ozone has a refreshing quality that helps to eliminate some of the existing odors. Ozone is usually created with a small amount of ultraviolet radiation. Some maintain that ozone is toxic, however, so it is best to carefully weigh your options before buying an ionizer.
Concentrations
The concentration of ozone appears to be directly related to its toxicity, according to the Environmental Protection Agency. The problem with refrigerator air ionizers is that they produce such a low, non-toxic level of ozone that they are ineffective in removing various air contaminants such as mold and bacteria. The overall sense that you get when reading the EPA's website and other Internet review websites is that these ionizers generally promise more than they can actually deliver.