Gas detection is crucial for maintaining air quality, particularly in the wake of the COVID-19 pandemic. CO2 monitors, a type of gas detector, have taken center stage in this conversation. These devices are widely used in various indoor settings, such as classrooms, gyms, workplaces, and offices, to track carbon dioxide levels and assess the risk of pathogen transmission. Some jurisdictions even mandate their use indoors. A standard CO2 monitor features adjustable alarm settings, enabling users to ensure compliance with different CO2 exposure limits and promptly detect and address any potential gas-related health risks in their environment.
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Key Figures of Merit to Compare CO2 Monitors?
Best CO2 Monitor?
There are many CO2 monitors on the market. Reputable brands include the following:
- Forensics Detectors CO2 Monitor
- Aranet4 CO2 Monitor
- Extech Carbon Dioxide Meters
- INKBIRD CO2 Monitor
- TempTop CO2 Air Quality Monitor
How Do I Select a CO2 Monitor?
To select the best carbon dioxide monitor that serves your purpose, follow this guide. In order to better understand your application and narrow down your selection, answer these questions:
- What carbon dioxide range do I need?
- What resolution do I need?
- How often will I use it?
- What is my budget and operating cost budget?
- Do I need a micro-pump or probe?
- Is it for personal protection or a stationary monitor?
- Do I need advanced functions such as data-logging, max features, or a CO2 monitor that complies with AB841?
How Long Does a CO2 Monitor Last For?
CO2 detectors last for a very long time compared to other gas sensors such as electrochemical cells. CO2 detectors are made up of NDIR sensors, solid-state electronic components that last between 5 to 20 years. The weakest component is usually the infrared source which may degrade over time.
What Is Carbon Dioxide (CO2) Gas?
CO2 is the chemical formula for carbon dioxide. It is a common gas that occurs naturally in the air. As of 2021, CO2 atmospheric outdoor levels are approximately 413 ppm. CO2 has many modern uses we take for granted, such as:
- CO2 is used for carbonation in drinks
- CO2 is used as dry ice for refrigeration
- CO2 is used as an inert gas in many industrial processes
- CO2 is used as a modified atmosphere packaging gas to extend food shelf life
Why Is CO2 Gas Important?
Carbon dioxide is one of the most important gases in our atmosphere, with a concentration of 413 ppm. Carbon dioxide is an essential gas as it helps to contain heat in our atmosphere by absorbing warmth from the sun. Without CO2 and its pivotal role in the greenhouse gas process, our planet would be miserably cold and inhospitable.
Carbon dioxide also plays an important role in plant and animal life, including photosynthesis and respiration.
Is Carbon Dioxide Heavier or Lighter Than Air?
Carbon dioxide is about 1.5 times heavier than air. This can be seen when dry ice is used at a wedding to provide the "dancing on a clouds" illusion. The carbon dioxide clouds stay low to the ground because CO2 is heavier than air.
What Does a CO2 Monitor Do?
A carbon dioxide monitor tracks the CO2 concentration levels in outdoor and indoor environments. It provides the user with a parts per million (ppm) reading, which represents the concentration of carbon dioxide.
A carbon dioxide monitor is sometimes called a CO2 monitor, CO2 analyzer, CO2 meter, CO2 detector, CO2 alarm, carbon dioxide sniffer, or carbon dioxide tester. All of these terms refer to a device that is capable of sensing and reporting carbon dioxide levels in real-time.
CO2 monitors typically read concentration in ppm and display this value on their LCD screen. Most CO2 monitors have an alarm that warns occupants if a certain preset level is exceeded. This helps users take action to remedy high CO2 levels.
CO2 monitors are also integrated in many heating and cooling systems that may trigger the HVAC system to switch operating modes.
How Is Carbon Dioxide Gas Detected?
Carbon dioxide is measured in the air using CO2 gas meters and monitors. Inside these monitors, a small CO2 sensor cells determines the amount of CO2 molecules in the air. CO2 monitors range from $50 to $1000. Most carbon dioxide monitors employ CO2 sensors with non-dispersive infrared (NDIR) sensing technology. An example of carbon dioxide monitors and what they look like is here.
How Does a Carbon Dioxide Monitor Work?
Carbon dioxide meters use NDIR, an infrared absorption technology that detects CO2 molecules. These molecules absorb radiation, which changes the light transmission intensity between an infrared source and detector. This change is analyzed by a photodetector which then outputs a voltage signal proportional to the CO2 concentration. Infrared absorption is the most efficient way to detect carbon dioxide gas. It is considered the "go-to" sensor technology for CO2 and is included is nearly all carbon dioxide monitors and analyzers.
CO2 Sensor Technology |
Working Principle |
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Non Dispersive Infrared (NDIR) |
Infrared light is emitted and then absorbed by the carbon dioxide molecules. The absorption is detected using a photodetector. Using the Beer-Lambert law, the IR absorption and CO2 concentration is determined. |
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What Are Safe CO2 Levels?
Various government agencies have recommended carbon dioxide gas exposure limits and emission levels. Some examples are shown in the table below.
Agency |
Recommendation / Requirement |
| California State Assembly Bill AB841 | Requires classrooms to monitor CO2 and alarm at 1,100 ppm |
| American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) | Recommends indoor CO2 concentrations be maintained below 1,000 ppm in schools and 800 ppm in offices |
| Washington State | Requires CO2 monitoring in restaurants, alarming at 450 ppm |
| German Federal Environment Agency | Recommends classroom and office CO2 levels below 1,000 ppm |
| Occupational Safety and Health (OSHA) |
5,000 ppm 8 hour TWA |
| National Institute for Occupational Safety and Health (NIOSH) |
5,000 ppm 8 hour TWA 40,000 ppm IDHL Immediately Dangerous To Life or Health |
| American Conference of Governmental Industrial Hygienists (ACGIH) |
5,000 ppm 8 hour TWA Ceiling exposure limit (not to be exceeded) of 30,000 ppm for a 10-minute period 40,000 ppm IDHL Immediately Dangerous To Life or Health |
What Are the Health Effects of Carbon Dioxide?
Carbon dioxide is in every breath we take as it exists at a concentration of 413 ppm in outdoor air. At this level, it is non-toxic.
The problem occurs when CO2 levels increase beyond 413 ppm. As carbon dioxide concentration increases, it is defined as a simple asphyxiant. A simple asphyxiant is a gas which displaces the normal oxygen in the air we breathe. Common symptoms include headache and drowsiness. At higher CO2 levels, rapid breathing, confusion, increased cardiac output, elevated blood pressure, and increased arrhythmias may occur. Breathing oxygen-depleted air will lead to death by suffocation.
Since CO2 is odorless and does not cause irritation, it is considered to have poor warning properties and requires careful monitoring.
Is Carbon Dioxide an Indoor Air Pollutant?
Yes it is. For many years, carbon dioxide measurements have been used to better understand airflow and guide the design of cooling, heating, and ventilation systems. High indoor CO2 levels are tied to poor health and lack of fresh air entering an indoor structure.
When there is poor air ventilation, the concentration of CO2 will increase. This results in pollution of the indoor space. CO2 monitoring allows occupants to know if CO2 levels are too high so corrective action can take place. Opening a window or door and turning on the ventilation system can help reduce indoor CO2 levels.
Is Carbon Dioxide Linked to COVID Transmission?
Carbon dioxide monitoring is an essential aspect of COVID-19 preparedness. When CO2 is exhaled, aerosols containing pathogens such as SARS-CoV-2 from COVID-19 are also expelled. Therefore, carbon dioxide can be used as a proxy for virus concentrations in the indoor air - as shown by research from the University of Colorado & Harvard School of Public Health.
Various government legislatures and professional organizations such as ASHRAE recommend CO2 indoor air quality monitoring to reduce the risk of COVID-19 infection. The Technical University of Berlin showed that increasing uncontaminated air reduces indoor concentrations of CO2 and other aerosols. In turn, this strategy of fresh air ventilation lowers one's infection risk.
Are CO2 Monitors Required in Classrooms?
Since the pandemic, various states have mandated carbon dioxide monitoring in classrooms.
For example, California Assembly Bill AB 841 requires CO2 monitoring in classrooms in an effort to reduce COVID-19 transmission and infection risk. The bill requires classrooms to monitor carbon dioxide and provide an alert when levels exceed 1,100 ppm. More info on this topic can be seen below:
What Is a CO2 Monitor Used For?
There is a plethora of carbon dioxide monitoring applications that we take for granted. Some under the radar uses are listed below.
CO2 for Indoor Air Quality and HVAC
Low cost NDIR-based carbon dioxide sensors provide indoor occupants with CO2 ppm readings. Typical requirements include wall-mounted or desk-mounted stand units, a detection range from 0 - 5,000 ppm, 1 ppm resolution, and an "always on" CO2 detection capability. See FD-CO2000.
CO2 for Headspace Analysis of Modified Atmosphere Packaging
Used in many food industries as a quality control check to ensure MAP equipment is operating to specification. Typical requirements include CO2 measurement range from 0 to 100%, 0.01% resolution, and a built-in pump. See FD-HA-CO2.
CO2 Gas in Equipment Processing & CO2 Leakage Detection
Many industrial systems and equipment incorporate CO2 gas supply where leak detection is important for worker safety. Continuous monitoring may be required using a CO2 analyzer and probe. Typical requirements include a CO2 measurement range from 0 to 100%, 0.01% resolution, and a built-in pump. See FD-600-CO2.
CO2 Monitor for Personal Exposure (Industrial)
Many industrial environments incorporate storage facilities that use 100% CO2 gas for industrial processes and dry ice for cold storage. Employees in such facilities require continuous personal CO2 monitoring for protection from high levels of CO2 exposure. A industrial continuous CO2 monitor in this case with industrial specification is required.
CO2 Gas in Biological Incubators
Incubators are used to grow and store biological samples, requiring a constant CO2 level of about 5%. Typically used by life science laboratories and research and development institutions. CO2 analyzer requirements include a CO2 measurement range from 0 to 100%, 0.01% resolution, and a built-in pump with small probe. See FD-600-CO2 (but with a smaller 4-inch probe for easy gas sampling).
Industrial CO2 Monitoring
Workplace settings such as laboratories, manufacturing facilities, factories, warehouses and public facilities require continuous CO2 monitoring. Industrial specification CO2 monitors are requires that are designed to continuously monitor and provide alarming or trigger ventilation and fan operation
Can a CO2 Monitor Be Used in a Car?
Yes, a CO2 monitor can be used in confined spaces including vehicles. When the vehicle HVAC system operates in recirculation mode, little or no fresh air enters the car cabin. Therefore, as occupants exhale, the CO2 levels can quickly accumulate. An example of CO2 accumulation during a vehicle trip is shown below.
What Is the Difference Between a Carbon Monoxide and Carbon Dioxide Monitor?
Never confuse carbon monoxide for carbon dioxide. They are very different gases with different physical properties and dangers to human health.
Carbon monoxide is a gas produced during combustion and is generally much more toxic than carbon dioxide.
What Can Cause a Carbon Dioxide Monitor to False Alarm?
A carbon dioxide detector is sensitive to humidity. H2O molecules are absorbed at the same infrared wavelength as CO2 molecules with a NDIR cell. Therefore, if you are operating in an extremely humid environment, gas sample conditioning may be required to reduce cross sensitivity.
How Can I Test My CO2 Monitor?
The best way to test your carbon dioxide detector is to take it outdoors to fresh air. It should read about 413 ppm. If it is off by 50 ppm or so, try to recalibrate the monitor.
If you have a CO2 meter that has 0.01% resolution and a % range, the best practice is to expose it to a higher concentration source, such as a bump can or gas cylinder. The user can simply spray the gas onto the device to confirm sensor, LED, and buzzer alarm operation. Generally referred to as bump testing, this is good practice, especially in personal protection applications where safety is paramount.
Will My CO2 Monitor Alarm if I Breathe on It?
If you breathe onto your CO2 meter, the detected levels will quickly increase. Exhaled breath has about 4% (40,000 ppm) to 5% (50,000 ppm) of CO2.
What Is Carbon Dioxide Gas Calibration?
Gas detector calibration is a technical procedure performed every 6 - 12 months to ensure your device is functioning accurately. Over time, gas detectors and their respective sensors degrade, some faster than others. When this happens, the only way to ensure accurate readings is via gas calibration.
This time period is typical for CO2 gas detectors employing NDIR sensor elements.
If you have an indoor air quality CO2 monitor in the ppm range, the unit can be calibrated to fresh outdoor air at 413 ppm.
If you have a CO2 meter or analyzer with a 0 - 100% range, you will typically calibrate in the mid-point of the range, i.e. 50% CO2 with a calibration gas bottle.
Be attentive and calibrate much more regularly if:
- The user is employing the device as an analytical tool where accuracy is paramount.
- The device is used in an extreme environment (temp and humidity).
- The user is performing a dangerous application. In this case, calibration and bump testing are mandatory since imminent injury or death will occur if the device fails.
What Is CO2 Meter Bump Testing?
- Bump testing is a procedure where the user exposes the detector to a small amount of “blast” target 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 and critical user applications.
- It is recommended to bump test when first purchased, followed by weekly tests. These checks are especially important in LIFE THREATENING and / or DANGEROUS applications in order to verify detector operation. See video explanation here.
- CO2 bump test gas is here.
How Do I Take Care of My CO2 Monitor?
- Store your carbon dioxide gas detector at a 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, or harsh chemicals.
- Clean the casing of your detector with a damp cloth.
- Store it in a stable location where there are no vibrations or continuous shaking.
How Do I Properly Use a CO2 Monitor?
When operating a carbon dioxide monitor, there are some important tips to consider. Obviously, be smart and read your product manual. Be sure to keep these tips in mind:
- Ensure the carbon dioxide detector is within its calibration period.
- Ensure the carbon dioxide detector has been bump tested and validated as operational.
- Carbon dioxide is heavier than air, so it tends to drop to the ground. If you are concerned about early warning of carbon dioxide, place your sensor low to the ground.
- When using a personal protection carbon dioxide meter, turn it ON, and keep it on your person. Set your alarms as desired.
- If performing analytical measurements, keep the unit stationary. Ensure humidity and temperature are also tracked and remain as constant as possible.
Can Human Senses Detect Elevated Carbon Dioxide Levels In Indoor Environments?
No, humans cannot directly smell carbon dioxide. While high CO2 levels can cause discomfort and drowsiness, the gas itself remains odorless, requiring monitors for detection.
What Is the Difference Between ppm and % CO2 Values?
The typical scale for CO2 concentration is ppm or %.
For indoor monitoring, ppm is typically used as CO2 levels range from 0 to 5,000 ppm. PPM stands for 1 part per million. So if we have 1 million parts per million, that would be 100%.
Conversion Example
CO2 % value = (CO2 ppm / 1,000,000) x 100%
For example, if we have 5,000 ppm, then we obtain
CO2 % value = (5,000 / 1,000,000) x 100%
CO2% value = 0.5%
Quick Conversion
100 ppm = 0.01%
1,000 ppm = 0.1%
10,000 ppm =1%
100,000 ppm =10%
1,000,000 ppm =100%
Are CO2 Monitors Required in Restaurants?
It depends on which state. For example, Washington State requires CO2 monitoring in restaurants with an alarm trigger at 450 ppm.
Final Words
Gas detection plays a vital role in monitoring carbon dioxide, a gas essential for our survival on Earth. CO2 levels also serve as an excellent indicator of pathogen transmission risk in indoor environments. In certain instances, schools and restaurants are mandated to use CO2 monitors to ensure safe air quality. The heightened demand for carbon dioxide meters has made quality CO2 monitors more affordable, with prices falling below $100. These gas detection devices are crucial for maintaining healthy indoor spaces and mitigating the potential spread of airborne pathogens by alerting occupants when CO2 levels exceed recommended thresholds.
About The AuthorDr. 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. 
Everyday 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 |