CO2 Measurement Methods

Introduction

Carbon dioxide (CO₂) is a greenhouse gas that affects the climate and the quality of life on Earth. Measuring the CO₂ level in the air is important for various applications, such as environmental monitoring, industrial process control, indoor air quality, and health and safety. There are different methods to measure the CO₂ level in the air, depending on the purpose and the range of concentration. Some of the common methods are:

Cavity Ring-Down Spectroscopy (CRDS)

This method uses a laser beam that is reflected inside a cavity with mirrors. The laser light is absorbed by the CO2 molecules in the cavity, and the time it takes for the light to decay is measured. This method is very precise and accurate, and can measure CO2 levels from ambient to high concentrations.

Non-Dispersive Infrared (NDIR) e.g. TechnolineWL1030

This method uses an infrared light source that passes through a sample of air. The CO₂ molecules in the air absorb some of the infrared light, and the remaining light is detected by a sensor. The amount of light absorbed is proportional to the CO₂concentration in the air. This method is simple and inexpensive, but less accurate than CRDS. It is widely used for indoor air quality monitoring and industrial applications.

Gas Chromatography (GC)

This method separates the different components of a gas mixture using a column and a carrier gas. The separated components are then detected by a detector, such as a flame ionization detector(FID) or a thermal conductivity detector (TCD). The CO2 concentration is calculated based on the peak area and the calibration curve. This method is accurate and sensitive, but requires more complex equipment and calibration. It is used for laboratory analysis and research purposes.

Photoacoustic Spectroscopy (PAS) e.g. Infineon PAS CO₂

This method uses a modulated laser beam to excite the CO2 molecules and measure the resulting sound waves. This method is very small, accurate, and low-power, and can be used for smart home and building applications45. Infineon's XENSIV™ PAS CO2 sensor is the first real CO2 sensor in an SMD package, and it can measure CO2 concentrations from 0 to 10,000 ppm5. It also meets the criteria of the WELL Building Standard, which is a global rating system for healthy buildings.

Metal Oxide (MOX) e.g. Carenuity SQ-Panel

This method uses a metal oxide layer that changes its electrical resistance when it interacts with gas molecules. This method is based on the detection of volatile organic compounds (VOCs) that are correlated with CO₂ levels. This method is compact, digital, and multi-gas, and can provide outputs such as equivalent CO₂(eCO₂), total VOCs (TVOC), and air quality index (AQI)78. ScioSense'sENS160 is a digital metal oxide multi-gas sensor that uses four sensor elements and an independent hotplate control to detect a wide range of VOCs and oxidizing gases with superior sensitivity. It is ideal for home appliances, IoT devices, building automation, and HVAC applications.

Conclusion

These are the main methods to measure the CO₂ level in the air. Each method has its own advantages and disadvantages, and the choice of the best method depends on the application and the requirements.