Ozone generators, as the name implies, are air purifiers designed to release ozone molecules into the surrounding air. The makers of these products indicate that this will lead to airborne pollutants reacting to the ozone in a way that renders them harmless to the health (see next section for more details).
Ozone consists of three oxygen atoms that have bonded to one another. The scientific designation of ozone is O3. It is probably best known for its presence in the "ozone layer" of Earth's upper atmosphere, which keeps much of the sun's radiation from reaching the planet's surface and thus makes life as we know it possible. However, when ozone comes into close contact with living organisms, including humans, it can result in a number of health problems, which will be detailed below.
(structure of an ozone molecule, 3 oxygen atoms and their charges - Image Source: Wikipedia)
Ozone generators create ozone using mechanisms such as an ultraviolet light or a corona discharge (a type of electrical discharge). The machine is also equipped with a fan that disperses the ozone out into the air. In theory, these ozone particles will come into contact with indoor air pollution and neutralize them -- for instance, by killing living pollutants such as bacteria.
As stated above, ozone consists of three atoms of oxygen. The substance normally called "oxygen" in day-to-day language is actually a bonded pair of oxygen atoms. Two oxygen atoms linked together in such a way are stable. When three are connected, however, the bond is far more easily broken. One of the oxygen atoms will tend to separate from the other two. Oxygen atoms by their nature easily bond with many other atoms, so the newly detached oxygen atom goes "looking," so to speak, for something else it can become attached to. When the oxygen atom finds something new and bonds with it, this fundamentally changes its physical nature. This is how ozone is supposed to work as an air purifier -- the free oxygen atom will, supposedly, render harmful pollutants safe.
The Environmental Protection Agency has studied the effectiveness of ozone as an air pollution removal tool and concludes plainly: "Available scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor air contaminants." The EPA considers much of the marketing conducted by makers of ozone generators to be misleading.
Scientific studies cited by the EPA have come to the following conclusions:
In short, ozone is not an effective tool in the fight against indoor air pollution. Other, more effective methods are available.
In addition to ozone's poor air-cleaning ability, it also needs to be pointed out that ozone itself is a serious pollutant that can contribute to a range of problems, particularly in the lungs. The free oxygen atoms can make their way into your respiratory system and cause damage to it. The EPA cautions that even if you purchase an ozone generator that claims to produce only "safe" levels of ozone, the actual amount of ozone being pumped into your air could be sufficient to cause danger.
When it comes to ozone generators, the question to ask is, "Why purchase an 'air purifier' that introduces more pollution into the air than it removes?"
Ozone generators are not effective at cleaning the air, nor are they safe. Those looking for an indoor air purifier are strongly advised to purchase some other type of purifier. A wide variety of ozone-free option exist (see HEPA air purifiers) and since the dangers of ozone have become better understood by the public in recent years, many air purifier manufacturers will explicitly guarantee that their products do not produce ozone.