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Dangers of Ozone Generators and Ozone Deodorizers

What is Ozone?

Ozone (O3) is an allotrope of oxygen (O2). That which exists in the stratosphere (between 10 ~ 16 km and 50 km above the ground) is called the ozone layer and accounts for about 90% of the ozone in the atmosphere. The remaining approximately 10% exists in the troposphere (10 ~ 16 km above the earth's surface).

Because of its strong oxidizing power, ozone is used for sterilization, virus inactivation, deodorization, decolorization, oxidation and decomposition of harmful substances, and biological activity. Ozone has a half-life of approximately 16 hours at a concentration of 1% (wt) in dry air, but when dissolved in water it is unstable and short-lived, returning to oxygen and water in a few dozen minutes. Because it does not remain in the water after treatment and has less change in taste and odor compared to chlorine, ozone is used in many countries to disinfect tap water instead of chlorine disinfection. It is also approved as a food additive in Japan and the United States.

Ozone is not something that can only be generated under special conditions; it can also be generated by laser printers, such as those found in ordinary companies, and air purifiers, deodorizers, and sterilizers found in homes and social welfare facilities that use high voltage or ultraviolet light.

Ozone Toxicity

Ozone as a gas is irritating to the respiratory system of the human body, and thus concentration control is required. The Journal of Occupational Health published by the Japan Society for Occupational Health sets the allowable concentration of ozone at 0.1 ppm as a standard to prevent health problems among workers. The definition of allowable concentration is as follows.

The allowable concentration is the concentration at which almost no adverse health effects are expected to be observed in workers exposed to a hazardous substance at a non-physically strenuous work intensity of about 8 hours per day, 40 hours per week, if the average exposure concentration of the hazardous substance is below this value.
Recommendations on Permissible Concentrations, etc. (FY2021) Journal of Occupational Health


The effect of ozone on living organisms is considered to be as shown in the table below. The concentration in terrestrial air is 0.00 to 0.03 ppm. (Atmospheric ozone and its measurement methods)

airborne concentration affect
0.01 ppm Olfactory thresholds of sensitive individuals
0.01 ~ 0.015 ppm Olfactory threshold in normal subjects
0.06 ppm No effect on olfactory performance in patients with chronic lung disease
0.1 ppm Unpleasant for normal people, irritation of nose and throat for most people
0.1 ~ 0.3 ppm Increased number of attacks in asthmatic patients
0.2 ~ 0.5 ppm Visual degradation after 3 ~ 6 hours exposure
0.23 ppm Increased prevalence of chronic bronchitis in long-term exposed workers
0.4 ppm Increased airway resistance
0.5 ppm Obvious upper airway irritation
0.6 ~ 0.8 ppm Chest pain, cough, increased airway resistance, dyspnea, decreased lung gas exchange
0.5 ~ 1.0 ppm Respiratory impairment, decreased oxygen consumption
0.8 ~ 1.7 ppm Upper airway irritation symptoms
1.0 ~ 2.0 ppm Coughing, hair-raising, fatigue, heaviness of head, thirst in upper orbit, 20% decrease in hourly lung capacity in 2 hours, chest pain, decreased mental activity.
5 ~ 10 ppm Dyspnea, pulmonary congestion, pulmonary edema, increased pulse, body pain, paralysis, coma
50 ppm Life threatening in one hour.
1000 ppm Dead in a few minutes

Ozone is such a substance Tadao Mizuno



Air Pollution by Ozone

Ozone is produced in nature as "photochemical oxidants" from nitrogen oxides and hydrocarbons contained in factory smoke and automobile exhaust gases, etc., and is also a cause of air pollution. (Incidentally, photochemical oxidants that accumulate and become foggy are called "photochemical smog.)

You may be thinking, "I hear about ozone depletion, shouldn't we be making ozone?",But stratospheric ozone and tropospheric ozone are two different things. In a nutshell, stratospheric ozone is good ozone and tropospheric ozone is bad ozone.
Tropospheric Ozone Increase: Good Ozone and Bad Ozone|Environmental Rituals No.67|National Institute for Environmental Studies

What is sick building syndrome?

As noted in "What is Ozone?", ozone is easily produced indoors today, and there is concern that indoor ozone concentrations may be rising. In particular, it has been noted that ozone reacts rapidly with terpene chemicals found in cleaning agents and air fresheners and can generate a number of secondary pollutants, including formaldehyde and other toxic air pollutants. In addition, the reaction of ozone with terpenes produces hydroxyl radicals, which react rapidly with organic matter and lead to the formation of other potentially toxic air pollutants.
Cleaning products and air fresheners: exposure to primary and secondary air pollutants - ScienceDirect

The cleaning agents also contain volatile organic compounds (VOCs), which, along with formaldehyde generated by reactions with ozone, contribute to sick building syndrome.

When living in a house contaminated by formaldehyde and volatile organic compounds (hereinafter referred to as VOCs) emitted from building materials, furniture, etc., one may experience complaints such as sore eyes and throat, headache, fatigue, and irritability. We call it "sick house syndrome.
Thinking about the sick house problem


The guideline value for indoor concentration of formaldehyde set by the Ministry of Health, Labor and Welfare is 0.08 ppm.
・Guideline Values for Indoor Concentration of Chemical Substances in Indoor Air (◆Yakusho-Houkokusho No. 117001, January 17, 1991)

However, measurements of formaldehyde concentration (detector tube method) and other parameters were conducted in 13 student apartments built within four years around Niigata University in the summer (July to September 2010) and winter (late November to early December 2010), with the following results: In summer, half of the houses had levels exceeding 0.08ppm.

Result, Furniture was relatively inexpensive, and the emphasis was on design and functionality, with few people taking into account its impact on indoor air quality. Half of the dwelling units had formaldehyde concentrations exceeding the guideline value of 0.08 ppm during the summer, and one dwelling unit exceeded the guideline values for ethylbenzene and styrene. In summer, units with high formaldehyde concentrations tended to have more household goods and higher room temperatures than other units, and even units with 24-hour ventilation had closed air supply vents, suggesting inadequate ventilation.
Volatile Organic Compound Concentrations in Student Apartments in Relation to Household Products



Generation of ozone by air purifiers

Various air purifiers are sold for the purpose of removing airborne particles and other particles from indoor air. However, some air purifiers, especially electrostatic air purifiers with corona discharge, generate ozone during operation, but many of them do not mention ozone generation in their catalogs. On the contrary, despite the fact that ozone is generated and that ozone generates many secondary pollutants, including formaldehyde and other hazardous air pollutants, some companies intentionally generate ozone by exaggerating the advantages of ozone generation, such as sterilization and deodorization, without informing general households of the disadvantages of ozone generation. Some models are even marketed as "ozone generators" or "ozone deodorizers" that intentionally generate ozone without communicating the disadvantages of ozone generation to the general public, and some models incorporate such functions into air purifiers.

Therefore, a study was conducted using 14 commercially available air purifiers (not including models that intentionally generate ozone) to examine the amount of ozone generated when the air purifiers were operating and the decay rate after they stopped in a 4 m3 chamber made of stainless steel plates. The results showed that ozone generation was observed in some of the electrostatic precipitator type and ionic type models, and that the concentration of ozone in the largest ozone generating models exceeded the general environmental standard of 0.06ppm even in actual rooms.
Ozone generated by air purifiers and factors affecting its indoor concentration

Another experiment was conducted in 2015 to measure the removal performance of formaldehyde from air purifiers, but the removal rate was in the 9% range at the point of no use, which is not effective.
Research on the removal performance of pollutants from household air purifiers and a method for predicting indoor concentrations Removal performance and degradability of formaldehyde

I hope you now understand the dangers of air purifiers, ozone generators, and ozone deodorizers. I hope the above was helpful. Please also see here!