The Best Carbon Dioxide Monitors (Expert Guide)
Air quality monitoring has become an important topic since the pandemic. Carbon dioxide (CO2) monitoring has been at the center of the conversation. CO2 meters are used to track air quality levels in classrooms, gyms, workplaces and offices. They are a fantastic proxy to pathogen transmission risk and in some cases, been mandated to be used indoors. A typical CO2 monitor has adjustable alarm settings to allow users to be compliant with various CO2 exposure limits.
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 at about 413ppm. CO2 has many modern uses we take for granted such as:
- CO2 is used for carbonation for drinks
- CO2 is used as dry ice for refrigeration
- CO2 is used as a 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. Our atmosphere has a level of 413ppm. Carbon dioxide is a important gas as it helps to contain heat in our atmosphere by absorbing heat from the sun. Without CO2 and its pivotal role in the natural greenhouse 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 the weight of air which makes it heavier. We have all seen when dry ice is used at a wedding to provide the "dancing on a cloud" illusion. The CO2 clouds stay low to the ground as CO2 is heavier than air.
What does a CO2 Monitor do?
A Carbon Dioxide monitor tracks the CO2 concentration levels in an outdoor or indoor environment. It them provides the user with a part 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. They are all referring to a device that has the capability of sensing and reporting to the user the carbon dioxide concentration level in air that has been detected in real-time.
CO2 monitor typically read concentration in part-per-million (ppm) and display this value on their LCD screen. Most CO2 monitors have an alarm that warms occupants if a certain CO2 level has been exceeded. This helps users take some action to remedy the high CO2 levels.
CO2 monitors are also integrated in many heating and cooling systems that may also trigger the HVAC system to switch operating modes.
How is Carbon Dioxide Gas Detected?
Carbon Dioxide is measured in air using CO2 gas meters and CO2 gas monitors. Within these monitors a small CO2 sensor cells exists that actually senses the CO2 molecules in the air. The CO2 detectors range from $50 up to $1000. Most CO2 monitors employ CO2 sensors that employ non-dispersive infra-red (NDIR) sensing technology. An example of carbon dioxide monitors and how they look like is here.
How does a Carbon Dioxide Meter Work?
Carbon dioxide meters work by using NDIR technology which is an infra-red absorption technology that detects CO2 molecules. CO2 molecules absorb the infra red radiation which changes the light transmission intensity between an infra-red source and detector. This change is detected by a photodetector which then outputs an electronic voltage signal that is proportional to the CO2 concentration. Infra-red absorption is the best and most efficient way to detect carbon dioxide gas. It is the "go-to" sensor technology for CO2 and is included is nearly all CO2 monitors and CO2 analyzers.
CO2 Sensor Technology
Non Dispersive Infra-Red (NDIR)
Infra Red light is emitted and then absorbed by the carbon dioxide molecules. The absorption is detected with a photodetector. Using the Beer-Lambert law the IR absorption and CO2 concentration is determined.
What are Safe CO2 Levels?
Various government agencies and associations have recommended carbon dioxide gas exposure limits and emission levels. Some examples are in the below table.
Recommendation / Requirement
California State Assembly Bill AB841
Requiring classrooms to monitor CO2 and alarm at 1100ppm
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
Requiring CO2 monitoring in restaurants and alarm at 450ppm
|German Federal Environment Agency||
Recommends classrooms and offices CO2 concentration should not exceed 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 in the outdoor fresh air at about 413ppm. At this concentration level, it is non-toxic.
The problem occurs when CO2 levels increase beyond 413ppm. When the CO2 concentration increases, it is termed a simple asphyxiant. A simple asphyxiant is a gas which reduces or displaces the normal oxygen in breathing air. 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 via high CO2 concentrations will lead to death by suffocation.
Since CO2 is odorless and does not cause irritation, it is considered to have poor warning properties, hence the importance of CO2 monitoring.
Is Carbon Dioxide an Indoor Air Pollutant?
Yes it is. For many years, carbon dioxide measurements have been used to better understand the airflow and mixing in indoor structures that helps guide the design of cooling, heating, and ventilation systems. High CO2 levels indoors is tied to poor health and lack of fresh air entering an indoor space.
When there is poor air ventilation, CO2 concentration will increase. Doing so pollutes the indoor occupied space. CO2 monitoring will allow one to know if CO2 levels are too high so corrective action such as opening a window, a door or turning on the ventilation system can take place.
Is Carbon Dioxide linked to COVID transmission?
Carbon Dioxide monitoring is becoming an imperative part of COVID-19 preparedness planning. CO2 is exhaled with aerosols containing pathogens such as SARS-CoV-2 from COVID-19 infected people and therefore can be used as a proxy of 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 are now mandating and recommending CO2 indoor air quality monitoring to reduce COVID-19 infection risk. If CO2 levels trend to the upside, the Technical University of Berlin showed that increasing uncontaminated air (fresh air ventilation) reduces the indoor CO2 concentration, reduces the aerosol concentrations which then in turn reduces ones infection risk.
Are Carbon Dioxide 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 CO2 and provide an alert when the carbon dioxide levels in the classroom have exceeded 1,100 ppm. More info on this topic is in the below video:
What is a Carbon Dioxide Meter used for?
There is a plethora of carbon dioxide monitoring applications that go under the radar and we take for granted. A generic list that captures some of them are below.
- Indoor Air Quality and HVAC: Low cost NDIR based carbon dioxide sensors are used to provide indoor occupants with the CO2 ppm readings. Typical requirements includes wall mounted or desk mounted stand units, a detection range from 0-5000ppm with 1ppm resolution with "always on" CO2 detection capability. See FD-CO2000.
- 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 includes CO2 measurement range from 0 to 100%, with 0.01% resolution and built-in pump. See FD-HA-CO2.
- Equipment Processing & Leakage: Many industrial systems and equipment incorporate CO2 gas supply and monitoring any leaks is important for safety. Continuous monitoring may be required or a CO2 analyzer and probe may be effective. Typical requirements includes CO2 measurement range from 0 to 100%, with 0.01% resolution and built-in pump. See FD-600-CO2.
- Personal Protection Equipment: Many industrial environments incorporate CO2 and 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. Typical requirements includes CO2 detectors ranging from 0 to 5%, with 0.1% resolution, that are light and have a belt clip and can operate 24 hours continuously with LED, buzzer and vibration alarms. See FD-90A-CO2.
- Incubators: Incubators are iused to grown and store biological samples and require a constant CO2 level of about 5%. Typically required by life science laboratories and research and development institutions. CO2 analyzer requirements includes CO2 measurement range from 0 to 100%, with 0.01% resolution and built-in pump with small probe. See FD-600-CO2 (but with a smaller 4 inch probe for easy gas sampling).
Can CO2 Monitors be Used in a Car?
Yes. A vehicle is a confined space. When the vehicle HVAC system operates in recirculation mode, little or no fresh air enters the car cabin. Therefore, as occupants are exhaling, 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 Detector?
Never confuse carbon monoxide for carbon dioxide. They are both very different gases. They have different physical properties and are harmful to human health in different ways.
Carbon monoxide is a gas produced during combustion and is generally much more toxic than carbon dioxide.
What can cause a Carbon Dioxide Meter to False Alarm?
A carbon dioxide detector is sensitive to humidity. H2O molecules are able to be absorbed at the same infra red 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 sensitivities.
How can I Test my Carbon Dioxide Detector?
The best way to test your carbon dioxide detector is to take it outdoors to fresh air. It should read about 413ppm. If it is off by 50ppm or so, try to re-calibrate the monitor.
If you have a CO2 meter that has 0.01% resolution and has a range in the % levels, such as 0-5% or 0-100%, best practice is to expose it to higher CO2 concentration source that comes in a bump can or gas cylinder. One simply sprays the gas onto the sensor to confirm sensor, LED, and buzzer alarm operation. This type of testing is generally referred to as bump testing and is good practice to undertake especially in personal protection applications where safety is paramount.
Will my CO2 detector alarm if I breath on it?
If you breath onto your CO2 detector, it will quickly increase. Breath exhalation has about 4% (40,000ppm) to 5% (50,000ppm) of CO2 concentration.
What is the Best Carbon Dioxide Meter brand?
There are many carbon dioxide detectors on the market. The reputable brands include the following:
- Forensics Detectors Carbon Dioxide Meters
- TSI Carbon Dioxide Meters
- Extech Carbon Dioxide Meters
- CO2Meters.com Carbon Dioxide Meters
- Vaisala Carbon Dioxide Meters
- RAE Honeywell Carbon Dioxide Meters
- RKI Instruments Carbon Dioxide Monitors
How do I select a CO2 Detector?
To select the best carbon dioxide detector that serves your purpose follow this guide. You need to first understand your application. To 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 and 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 do CO2 meters last for?
CO2 sensors actually last for a very long time compared to other gas sensors such as electrochemical cells. CO2 detectors are made up of NDIR sensors that are solid state electronic components that last between 5 to 20 years. The weakest component is usually the infra red source which may degrade over time.
What is Carbon Dioxide Gas Calibration?
Gas Detector calibration is a technical procedure undertaken every 6 to 12 months to ensure your gas detector is functioning accurately. Over time, gas detectors and their respective sensors degrade, some faster than others, and 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 that is in the ppm range, most often the unit can be calibrated to fresh outdoor air which is 413ppm.
If you have a CO2 meter or analyzer with a 0-100% range, typically one will 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 user is using the device in an extreme environment (temp and humidity).
- The user is undertaking an imminently dangerous or extreme application. Calibration and bump testing is mandatory since imminent injury or death will occur if the device fails.
What is CO2 meter Bump Testing?
- Bump testing is a procedure when one exposes the gas 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 detection operation and build user confidence, particularly in hazardous and critical user applications.
- It is recommended to bump test when first purchased. Weekly thereafter especially 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 Detector?
- Store your carbon dioxide gas detector in 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 where no dust or particles exist.
- Store is away from any exhaust gas, concentrated vapors, 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 use a CO2 meter?
When operating a carbon dioxide monitor, there are some important tips to consider. Obviously, be smart and read your product manual. But do keep these tips in mind:
- Ensure the carbon dioxide detector / analyzer is within its calibration period.
- Ensure the carbon dioxide detector / analyzer has been bump tested and validated 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.
- When using a personal protection carbon dioxide meter, turn it ON, and keep it on your man. Set your alarms as desired.
- If undertaking analytical measurements, keep the unit stationary. Ensure humidity and temperature is also tracked and are as constant as possible.
What is the difference between ppm and % CO2 values?
The typical scale of concentration for CO2 is ppm or %.
For indoor monitoring, ppm is typically used as CO2 for indoor monitoring ranges from 0 to 5000ppm. PPM stands for 1 part per million. So if we have 1 million parts per million, that would be 100%.
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%
100ppm = 0.01%
1,000ppm = 0.1%
Are Carbon Dioxide Monitors Required in Restaurants?
It depends in which state. For example, Washington State requires CO2 monitoring in restaurants with an alarm trigger at 450ppm.
Carbon dioxide is a critical gas for our survival on planet earth. CO2 is a fantastic proxy to pathogen transmission risk and in some cases, has even been mandated to be used in schools and restaurants. Due to the increased CO2 meter demand a good quality CO2 monitor can be purchased below $100.
About The Author
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.
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 having a cold beer.
Read more about Forensics Detectors here.