Gas detection is crucial when it comes to monitoring ozone levels in the air, and an ozone detector is the key tool for this purpose. These analyzers measure the concentration of ozone gas in parts per million (ppm), providing essential information for safety and environmental monitoring. However, the unique nature of ozone as an unstable gas presents challenges in detection. Ozone decays to form oxygen based on factors such as temperature, humidity, time, and air agitation, making consistent measurements tricky. To ensure accurate gas detection, it is vital to understand the intricacies of ozone detectors and follow best practices for their use. This guide offers essential information and tips to help users obtain reliable ozone measurements through effective gas detection techniques.
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Best Ozone Detector
The best ozone detector is the Forensics Detectors Ozone Detector. Why? Because it is calibrated in the USA to NIST traceable sources. This is the only way to be assured of maximum accuracy of your ozone ppm readings.
What Is Ozone Gas?
Ozone is a simple gas made up of three oxygen molecules with the chemical formula O3. It has unique behavioral characteristics. It is an unstable gas and decays to oxygen, meaning that it is tricky to handle and measure.
Ozone is a strong oxidizing agent and offers interesting disinfectant properties to effectively kill fungi, bacteria, and viruses. It is often used in "cleaning" situations. For example, ozone is used in transportation applications to clean police vehicles, transit buses, and commercial passenger aircraft.
Why Is Ozone a Special Gas?
Ozone is a special gas because it is unstable and decays to oxygen over time. It cannot be stored in a gas bottle. This unique characteristic makes it tricky to obtain repeatable ozone measurements. Ozone gas also has oxidization properties, making it a useful disinfectant for cleaning and abatement companies. Thanks to ozone's unique therapeutic properties, it is also used throughout medical therapies and applications.
How Is Ozone Gas Measured?
Ozone is measured in the air using low cost gas meters and ozone detectors. These devices cost between $300 and $5000. Typically, low cost detectors employ electrochemical sensors. These are galvanic cells that output voltages proportional to the ozone concentration. These cells are useful in the ppm ozone concentration range.
More expensive ozone detectors employ ultraviolet (UV) absorption technology. Ozone molecules in the air absorb UV radiation. When the change in light absorption is measured by photodetectors, the detector outputs a proportional electronic signal. UV absorption is the best way to detect low levels of ozone in the parts per billion (ppb) range.
How Do Ozone Sensors Work?
Ozone detectors, meters, and analyzers employ sensor elements to detect O3 gas molecules. These sensors come in three varieties: (1) electrochemical cells, (2) semiconducting metal oxide sensors, and (3) ultraviolet absorption sensors.
Ozone Sensor Technology |
Working Principle |
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Electrochemical Cells |
Ozone molecules interact with metal electrodes through a redox reaction, generating a linear voltage output proportional to the ozone concentration. |
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Semiconducting Metal Oxide |
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Ultraviolet (UV) Absorption |
Ultraviolet light is emitted and absorbed by ozone at 254 nm. The absorption is detected with a photodetector. Using the Beer-Lambert law, the UV absorption and ozone concentration is determined. |
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What Level of Ozone Is Safe? Acceptable?
Various government agencies have recommended ozone gas exposure limits and emission levels. Some examples are shown in the table below.
Agency |
8 hour TWA |
Other |
| Occupational Safety and Health (OSHA) | 0.1 ppm |
0.3 ppm over 15minutes |
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National Institute for Occupational Safety and Health (NIOSH) |
0.1 ppm | 5 ppm IDHL Immediately Dangerous To Life or Health |
| US Environmental Protection Agency (EPA) | 0.07 ppm | |
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Food and Drug Administration (FDA) - ozone output of indoor medical devices 21CFR801.415 |
0.05 ppm output & accumulation | |
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American Conference of Governmental Industrial Hygienists (ACGIH) |
0.1 ppm | |
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UL2998 - Environmental Claim Validation Procedure (ECVP) for Zero Ozone Emissions from Air Cleaners |
0.005 ppm | |
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UL867 - Standard for Electrostatic Air Cleaners Any device that requires power to clean the air |
0.05 ppm | |
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American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Environmental Health Committee |
0.01 ppm | |
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California Air Resources Board (CARB) ozone emissions electronic air cleaners |
0.05 ppm |
Is Ozone Safe to Breath?
No, it is not. If you inhale ozone, a cough response is immediately triggered. The National Institute for Occupational Safety and Health (NIOSH) has established the Immediately Dangerous To Life or Health ozone concentration as 5 ppm.
When working with ozone, make sure you are in a well-ventilated area and have a personal ozone meter to warn you of high levels.
More on the health effects of ozone can be found here.
What Does Ozone Smell Like?
Ozone has a familiar photocopier room smell. You may not have noticed it, but the ultraviolet light emits ozone in photocopier rooms or when you print a lot of pages at home.
The ozone odor is sometimes described as a "clean," electric smell.
Can I Determine Ozone Concentration Using My Nose?
No, you cannot. Although your nose can detect very low levels of ozone < 0.02 ppm, the nose quickly adapts and experiences olfactory fatigue.
Olfactory fatigue is used to describe losing sensitivity to specific odors after exposure. When continuously smelling the same scent, your nose and brain will adapt and lose sensitivity to that smell over time. Eventually, you will not recognize the odor, hence the term olfactory fatigue.
Olfactory fatigue will dissipate when the smell is removed, so your sensitivity will return to normal after some time. Each person has different sensitivities to different smells, which also varies with age.
All in all, don't bother trying to correlate the potency of ozone scent to a particular amount of ozone. It simply is not a reliable method of detection.
Can Ozone Be Used as a Cleaning Disinfectant?
Yes, it can. Ozone is a strong oxidizing agent that can kill bacteria, molds, fungi, and viruses.
When ozone generators or electrostatic air purifiers create ozone, the gas can reach every corner in the room, making it a very effective and residue-free approach compared to spray or chemical methods.
The efficacy in killing microorganisms like bacteria, fungi, and viruses depends on the ozone concentration, exposure time, temperature, humidity, and air agitation.
All in all, ozone is comparable to other disinfectant methods, such as UV light and chemical disinfectants.
What Level of Ozone Is Needed to Kill Pathogens?
When using ozone to kill pathogens, there are two components that must be determined: (1) concentration and (2) exposure time. Many resources have developed efficient protocols for a variety of pathogens, but each has its intricacies. We recommend referencing the latest literature in the field using Google Scholar. As a guide, here are some examples:
Pathogen |
Ozone Concentration (ppm) |
Time (minutes) |
| Bacteria | 0.3 - 2.3 | < 20 |
| Virus | 0.2 - 4.0 | < 30 |
| Mold | 3.0 - 5.0 | 60 |
| Fungi | < 0.3 | < 2 |
What Is an Ozone Detector Used For?
There are many uses of ozone detectors. Some examples include:
Personal Protection Equipment
Portable ozone detectors are clipped onto workers to provide personal protection, ensuring safe exposure levels. For example, ozone is used to disinfect aircraft. When workers are cleaning, portable ozone detectors provide protection from elevated levels of ozone exposure.
Sanitization / Disinfectant / Cleaning
Portable ozone detectors are used to verify ozone concentrations in crop grow rooms. This ensures high yield and destroys pathogens such as fungi, microbes, bacteria, and viruses. High range ozone detectors are occasionally required for this purpose.
Occupation Space Safety
Many water treatment facilities employ ozone to disinfect storage containers. On a production line of small units, wall-mounted ozone monitors are placed to protect employees from equipment malfunctions and large ozone emissions.
Ozone Therapy & Medical
Ozone has many medicinal benefits, as it is used to disinfect and treat disease. It inactivates bacteria, viruses, fungi, yeast, and protozoa. Ozone has also been used to treat diseases such as infected wounds, circulatory disorders, geriatric conditions, macular degeneration, viral diseases, rheumatism/arthritis, cancer, SARS, and AIDS. Therefore, portable low-level ozone gas detectors are required by medical workers to ensure they are working within safe ozone exposure limits.
How Do I Select an Ozone Detector?
In order to select the best ozone detector, follow this guide. To understand your application and narrow down your selection, answer these questions:
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What ozone range do I need?
- Typical ranges include:
- 0-1ppm with 0.001ppm resolution (1ppb)
- 0-5ppm with 0.01ppm resolution
- 0-20ppm with 0.1ppm resolution
- 0-100ppm with 1ppm resolution
- 0-1000ppm with 1ppm resolution
- 0-10,000ppm with 10ppm resolution
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What resolution do I need?
- Resolution depends on the accuracy you require and maximum full scale range of the detection range you select. Do not confuse however resolution with accuracy.
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What is my budget and operating cost budget?
- Your budget will most likely dictate the performance on the ozone meter. However, never forget the accuracy of any gas detector is most dependent in the quality of its calibration. Ensure it has been calibrated to NIST traceable ozone. Especially for ozone since only a few labs in the USA are able to calibrate to ozone.
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Do I need a micro-pump or probe?
- This will depend on your application. Try not to use a external pump. If you need flow or a pump, ensure the meter or analyzer has been calibrated with a built in pump version ozone analyzer.
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Is it for personal protection or to remain within the OSHA exposure levels?
- If so, you require a 0.01ppm resolution detector that is accuracy and suitable for lower levels of detection.
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Do I need stationary wall-mounted unit or a portable unit?
- Avoid using a portable unit as a 24-7 monitor. The portable units due to their internal battery charging, are not suitable to remain in the ON position for a long period of time. In addition, their housing and alarming may not be adequate for a room monitoring situation, which itself may pose a large problem.
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Why Would I need a HIGH RANGE (0-100ppm) Ozone Detector?
- A high range OZONE detctor is often used by abatment treatment companies, manufacturing, R&D and scientists to track higher levels of OZONE up to 100ppm.
What Are Ozone Detector Applications?
Examples of some real ozone detector applications used by our customers:
- A customer requires a generic portable ozone detector to confirm a 2 ppm level to kill fungus. Solution: 0 - 20 ppm with 0.1 ppm ozone gas detector is recommended.
- A customer requires a personal protection ozone meter to protect from OSHA 8-hour exposure recommendations. Solution: A low level ozone detector with 0 - 5 ppm range and 0.01 ppm resolution is recommended.
- A customer must disinfect a bus with 40 ppm ozone and would like to track ozone levels when cleaning. Solution: A high range 0 - 100 ppm ozone gas detector is recommended.
- A customer requires a very sensitive ozone analyzer to perform pre-tests for air purifier products before UL867 accreditation. Solution: A ppb UV ozone analyzer is recommended with resolution down to 0.001 ppm.
- A customer requires 24/7 protection from ozone machine leakage with relay switching capability. Solution: A wall-mounted ozone monitor is recommended.
- A customer requires ppm levels of ozone detection for university research. The data acquisition is required every second for publication data. Solution: A 0 - 20 ppm model 600 ozone analyzer with data logging functionality is recommended.
How Long Do Ozone Detectors Last?
- Ozone detectors using electrochemical cells last between 24 to 36 months.
- Ozone detectors using semiconducting metal oxide sensors last about five years.
- Ozone analyzers using ultraviolet absorption detection last over ten years.
What Is Ozone Calibration?
Ozone (O3) is a unique gas and cannot be calibrated with a calibration bottle setup like most gases. As ozone is an unstable gas, it cannot be stored at a fixed concentration in a gas cylinder.
Therefore, ozone must be generated on-site. The produced ozone must be calibrated to a NIST traceable source to ensure correct calibration. Only a few laboratories in the USA have the expensive, NIST calibrated equipment required to perform ozone detector calibration.
As an example, the Forensics Detectors Ozone USA NIST Traceability Procedure is highlighted here. Forensics Detectors provides ozone calibration services, which can be purchased here.
What Is Ozone Bump Testing?
Bump testing is a procedure when the user exposes the ozone detector to a small amount of “blast” gas to ensure the detector operates and alarms as programmed.
The function of this test is to verify proper operation and build user confidence, particularly in hazardous applications. It is recommended to bump test your ozone detector when first purchased, followed by weekly tests. This is especially important in LIFE- THREATENING and / or DANGEROUS applications. See video explanation here.
Ozone bump testing is performed using a small ozone generator.
How Do I Take Care of My Ozone Detector?
- Store your ozone detector at normal room temperature - about 70F with 50% RH (well within operating specifications).
- Store it away from electromagnetic or magnetic sources, such as phones.
- Store it in a clean environment with no dust or particles.
- Store it away from any exhaust gas, concentrated vapors, and harsh chemicals.
- Clean the casing of your detector with a damp cloth.
- Store it in a stable place where there are no vibrations or continuous shaking.
How Do I Properly Test for Ozone Gas?
When operating an ozone detector, there are some important tips to consider given the unique nature of ozone. Be smart, read your product manual, and keep the following tips in mind:
- Ensure the ozone detector is within its calibration period.
- Ensure the ozone detector has been bump tested and validated as operational.
- Ozone tends to drop to the ground since it is heavier than air. If you are concerned about early warning, place your sensor low to the floor.
- If you are using ozone as a disinfectant, ensure that you have enough fans running in your indoor environment. Forced air mixing of ozone will ensure it reaches all the small spaces and will not remain stagnant.
- When using a personal ozone detector, turn it ON, and keep it on you. Set your alarms as desired.
- If you smell ozone, it is probably present at levels lower than your alarm level presets due to your sensitive sense of smell. Take this as a sign that ozone is present and keep your eyes on the ozone concentration.
- Refrain from using accessory pumps or probes. Do so only if required and keep the tubing as short as possible.
- If performing analytical measurements, keep the unit stationary. Ensure humidity and temperature are also tracked and kept as constant as possible to obtain repeatable and comparable results.
- If performing low level ozone measurements < 5 ppm with a portable detector, ensure the gas detector is stationary.
- Keep ozone's heaviness into consideration when testing. This means that the measured ozone gas concentration will vary based on height.
Should I Use a Pump With My Ozone Detector?
There are two types of ozone detectors:
- Diffusive ozone detectors, where there is no forced air and natural diffusion facilitates detection of O3 molecules.
- Forced air or pumped air ozone detectors. This is where a micro-pump or pump accessory is integrated within the detector that forces sampled air to the sensor head.
When possible, it is best not to agitate the ozone and use diffusive detection. This is because as ozone tends to decay more quickly when agitated. In other words, the ozone breaks down faster. A pump or probe accessory may be required for point sampling. In this case, the addition of the pump or probe will agitate the ozone and increase its decay time, reducing the detected ozone concentration. Be aware of this effect as we always get the question, "why am I detecting less ozone when I attach the probe?"
Avoid any accessory pumps or probes and only use them as necessary to ensure maximum accuracy. If you plan to use a probe, there are two things you should do:
- Ask the manufacturer to calibrate the ozone with the pump attachment.
- If not calibrated with the pump, keep the tubing as short as possible.
Can My Ozone Detector Measure Outdoor Ozone Levels?
Low cost ozone detectors in the ppm range cannot measure outdoor ozone levels. This is a classic mistake we sometimes see our customers making. A generic 0- 20 ppm detector with 0.1 ppm resolution will not be able to detect atmospheric ozone.
The outdoor ozone concentration is in the parts per billion (ppb) concentration range. To detect ozone in the ppb range, you need a UV absorption analyzer. UV detectors are the only devices that can reliably and accurately measure ozone in the ppb range. This is a sophisticated piece of equipment that requires technical training to operate properly. In addition, UV analyzers are very expensive. Technical considerations such as temperature, humidity, and sampling techniques are required to ensure consistent and accurate measurements.
If you are a novice and are curious about your outdoor ozone levels, we recommend using Airnow. Enter your zip code to obtain the ozone levels from your local air quality station.
Can My Ozone Detector Measure the Output of My Ozone Generator?
No, not likely. Ozone generators typically produce thousands of ppm of O3. Do not use your standard (0 - 20 ppm) detector to test the output of your ozone generator as it will permanently damage the sensor. Only use an ozone detector to test the output if you are absolutely certain the range of the meter is within the output range. For example, if you have a custom built ozone meter with a range from 0 - 10,000 ppm, then testing 1000 ppm of ozone will be OK.
However, ozone generators are typically at an ozone output of mg/hr or g/hr. See the next section to convert to ppm and determine the expected ppm range - which will then help narrow down the appropriate ozone detector range.
How Do I Convert Ozone from mg/hr to ppm?
Customers with an ozone generator typically wish to purchase a detector to determine the output concentration. Ozone generators produce very high concentrations of ozone, often close to or over 1000 ppm. Be careful not to place the ozone detector at the output of any generator. You will blow it out!
Ozone generators are typically rated on ozone output based on gravimetric and time metric units, such as a mg/hr. This can be converted to ppm using the conversion factors below:
1 ug/mL = 1 mg/L = 1g/m3
1 g/m3 = 1 mg/L = 1 ppm of ozone in water (mass)
1 g/m3 = 467 ppm of ozone in air (volume)
1 ppm = 2.14 mg/m3 in air (by volume)
Let's consider an example:
What is the ozone concentration in ppm at the output of my ozone generator with a 200 mg/hour @ 2 LPM rating?
So at 2 LPM (liters per minute), after one hour, there would be 2 x 60 = 120 liters emitted since there are 60 minutes in one hour.
Within the 120 liters, there are 200 mg of ozone generated. So, we need to obtain a mg/L unit. A simple division of 200 / 120 = 1.67 mg/L.
From the conversions, we know that 1 mg/L = 1 g/m3, therefore:
Can You Smell Ozone?
Yes, ozone has a distinctive sharp, clean smell often noticed before thunderstorms. It's similar to chlorine and described as "electrical" or "metallic."
Final Words
Gas detection for ozone is the most challenging among all gases due to its unique physical properties. When selecting an ozone detector, it is crucial to conduct thorough research and ask detailed questions, particularly about NIST ozone traceability calibration, as not all detectors are created equal. For most applications, low-cost electrochemical cells provide adequate gas detection capabilities. However, if measuring ozone in the parts per billion (ppb) range is necessary, investing in a UV analyzer, which typically costs over $3000, is essential. Proper research and understanding of the specific gas detection requirements are vital to ensure accurate and reliable ozone measurements.
About The AuthorDr. Kos Galatsis ("Dr.Koz") is the President of FORENSICS DETECTORS where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters and gas analyzers. He has been designing, building, manufacturing and testing toxic gas detection systems for over 20 years. 
Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and enjoying the outdoors. Read more about Forensics Detectors here. Email: drkoz@forensicsdetectors.com |