CO2 in Controlled-Atmosphere Storage

Controlled-atmosphere (CA) storage adjusts the air composition — lower O2, higher CO2 than ambient air — to slow down the natural respiration of fruit and vegetables and extend their shelf life during long-term storage and transport. For the general principles of infrared CO2 measurement, see the technical note on how to measure CO2.

This note focuses on why CO2 is measured alongside O2 and humidity in this type of room, and on the particular challenge of instrumenting a cold, consistently high-humidity environment over time.

This note covers

• What controlled-atmosphere storage is and why CO2 is measured
• The challenge of measuring in cold, high relative humidity
• Instruments suited for cold storage and transport

What Controlled-Atmosphere Storage Is and Why CO2 Is Measured

In a controlled-atmosphere room, O2 concentration is lowered and CO2 raised relative to ambient air, alongside strict temperature and relative humidity control. By reducing available oxygen and raising CO2, the respiration rate of the stored fruit or vegetable slows down and ripening is delayed — allowing the storage period to be extended significantly without loss of quality.

The balance is delicate: too little CO2 fails to achieve the intended effect, but an excess can cause physiological damage to the product (for example, internal browning or spotting in some apple varieties). That's why sensor accuracy and stability over the whole storage period — which can run for several months — matter as much here as in any industrial process application.

The Challenge of Measuring in Cold, High Relative Humidity

Controlled-atmosphere rooms typically operate near 0°C, with high relative humidity to prevent dehydration of the stored product. These are exactly the conditions under which many electronic sensors lose accuracy or suffer condensation on their optical components.

A probe designed for this environment needs a wide operating temperature range (including sub-zero temperatures), a housing rating suited to humidity and dust, and internal compensation for temperature, pressure and humidity so the CO2 reading stays stable throughout the whole storage cycle.