Ionic air purifiers derive from a multitude of technologies, all of which contain one or more beneficial reactive agents that claim to clean the air that we breathe. Manufacturers willingly publish test results to demonstrate the potency of these reactive agents against harmful contaminants.

Safety First – Beneficial Reactive Agents

Unfortunately, manufacturers are not as forthcoming with information on the potential harm to human tissue of users who are exposed to the reactive agents. The in-depth article dealing with this aspect is posted at

Safety First Redux – Unintended By-products

Manufacturers are also not forthcoming about the by-products of their technology. Unbeknownst to many users, all ionic air purifier technologies generate by-products apart from the beneficial reactive agents. They are not deliberately produced but are simply unintended products resulting from current technological constraints.

Ozone, a component pollutant of smog, is the most common of these by-products. Smog, which hangs like a foggy cloud over some cities, is typically produced by the reaction of sunlight on automotive emissions such as carbon monoxide. Ozone in smog is blamed for many ills.

Please note that this article is not a discussion about ozone generators, a class of air purifiers that deliberately produces ozone in high enough concentrations to eliminate airborne contaminants. For instance, some hotels use ozone generators to get rid of tobacco smoke from rooms when they are being prepared for the next guest.

It is commonly accepted that ozone generators pose a danger to human tissue because ozone is an extremely reactive oxidizing agent. However, for some strange reason, ozone generators are still freely sold to home users as air purifiers. This controversy probably warrants another round of in-depth research in future.

All Ionic Air Purifiers Produce Some Ozone As A By-product

The focus of this article is on ionic air purifiers that do not deliberately produce ozone. There is no dispute that all ionic air purifier technologies are currently unable to completely eliminate ozone in the process of producing their beneficial reactive agents, be they negative ions, bipolar ions or plasmacluster ions and so on. It is a question of how much ozone is produced as an unintended by-product and at which point it becomes unhealthy and harmful to users of the ionic air purifier.

Most manufacturers emphasize that the ozone produced by their technology is very minimal. Often, they claim that it is way below 50 parts per billion (ppb), a measure of ozone concentration commonly cited by various parties around the world. Interestingly, there is no established legislation, only guidelines, regulating that ionic air purifiers cannot produce ozone in excess of 50 ppb. This leads us to the next question. 

Is Ozone Concentration At 50 ppb Safe?

This is the million dollar question 空氣清新機推薦 in the multimillion dollar ionic air purifier industry.

It is an even more important question for users (who typically have respiratory problems) of such purifiers since they may be harming themselves after spending good money on what they believe to be beneficial to their health. It should also be of great concern to health authorities since they are entrusted with setting safety standards that govern manufacturers and that users rely on when they use such equipment.

One would assume that the 50 ppb limit was scientifically set by some authorities, either medical or governmental. Shockingly, this does not seem to be the case. In fact, a prominent environmentalist suggested that this limit was arbitrarily set in the US FDA Amendment Act 1972 without any scientific basis. Yet, the 50 ppb figure is commonly cited, not just by manufacturers of ionic air purifiers but by health authorities all over the world as well. 

To add to the controversy, the 50 ppb limit under the US FDA Act only applies to an air purifier that is sold as a medical device! Now, that’s easy to get around. It is not common to see air purifiers being advertized as medical equipment. They are typically sold as appliances for improving air quality in the home, office, factory or school. But to their credit, manufacturers of many ionic air purifiers are voluntarily using 50 ppb as a safety limit.

There is also some measure of control imposed by the US Consumer Safety Products Act which covers ionic air purifiers that are not sold as medical devices. In a 2006 study, a US Consumer Product Safety Commission found that the 50 ppb ozone limit appears to be safe. But the Commission did highlight that ozone also enters into human dwellings from outdoor air, the so-called ambient air. This may elevate the actual ozone concentration above 50 ppb when an air purifier is being operated. Strangely again, there is no legislation in the US Consumer Safety Products Act about the 50 ppb ozone limit.

California Takes The Lead – Manufacturers Of Ionic Air Purifiers Take Note!

In October 2008, the US state of California took the first steps to regulate compliance with the 50 ppb ozone limit. It is aimed primarily at ozone generators but the regulation also covers ionic air purifiers. Serious players in the industry should be factoring this very significant development in their strategies if they do not want to see their Californian market share “terminated” (pun intended).

As users of ionic air purifiers, it is also our responsibility to take the 50 ppb ozone limit even more seriously. In scrutinizing the technical specifications of any air purifier, additional factors to consider  include noting that:

(1) the 50 ppb limit should be the average concentration over a 8-hour period;