How Altitude Affects CO2 Readings
Altitude makes a difference when you are measuring CO2 levels. CO2 sensor modules are calibrated at sea level, and are not designed to automatically compensate for higher altitudes.
CO2 sensors need either a manual offset using a barometer or lookup table for altitude compensation, or a built-in barometric pressure sensor to automatically compensate for the change.
Altitude Compensation: Identifying the Problem
A customer once reported a “defective” CO2 sensor that read 335 ppm outdoors after zero calibration. The problem? They lived in Colorado, roughly 5,000 feet above sea level. At that altitude, barometric pressure drops to about 632 mmHg -causing the reading to be roughly 15% lower than at sea level.
Rule of Thumb: CO2 levels change by approximately 3% for every 1,000 feet (300 m) above sea level.
Atmospheric Pressure and CO2 Measurement
Atmospheric pressure (AP) is the weight of air above you. It decreases as you climb in altitude. At sea level, AP is:
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1,013.25 hPa
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29.921 inHg
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760 mmHg
At 5,000 ft (Denver), AP is about 632 mmHg.
A CO2 sensor calibrated for 400 ppm at sea level would read:400 × (632 / 760) = 332 ppm
This difference is critical for applications like greenhouses or laboratories, where precise CO2 control is essential.
Here’s an example.
The city of Denver, Colorado is approximately 5,000 feet above sea level. At this altitude, the atmospheric pressure is 632 mmHg (barometric pressure table). A CO2 sensor calibrated at 400ppm at sea level would read 400(623/760) or 332ppm.
Note that while CO2 sensor modules do not automatically account for changes in altitude from sea level, they can be recalibrated for this. And some CO2 meters have built-in barometers that can compensate in real time. So if you are at high altitudes and need extremely accurate CO2 level readings, you should look for these features before making a purchase.
Why Accurate CO2 Readings Are Critical at High Altitude
High-accuracy CO2 readings matter for:
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Agriculture & Greenhouses – Incorrect readings can lead to over- or under-fertilization with CO2
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Indoor Air Quality Monitoring – Misinterpreting ventilation needs
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Scientific Research – Incorrect baseline values can compromise experiments
If a greenhouse grower in Denver wants 1,000 ppm, the sensor must be set to about 1,150 ppm to account for altitude.
Altitude Compensation for Oxygen Sensors
Like CO2 sensors, oxygen sensors require pressure compensation. The standard 21.9% O₂ value assumes standard temperature and pressure (STP). At Colorado elevations, oxygen concentration drops to 17.3%.
Before purchasing, check if your sensor has automatic barometric compensation or if you will need a lookup table/manual correction.
Here's a handy chart to show you the differences. Before purchasing an oxygen sensor check whether it is automatically compensated for pressure with a barometric pressure sensor on-board, or if you will need to adjust the oxygen level either by a lookup table or with a separate barometric pressure sensor.
Choosing a CO2 Sensor with Altitude Compensation
When selecting a CO2 sensor for use above sea level:
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Look for on-board barometric pressure sensors for real-time adjustment
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Check manufacturer specifications for altitude calibration range
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Consider whether the device supports manual altitude entry for field recalibration
Industries Most Affected by Altitude-Driven CO2 Variations
Altitude compensation is particularly important for:
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Mountain-based breweries – fermentation monitoring accuracy
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Mining operations – safety compliance in underground environments
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Sports training facilities – altitude performance research
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Remote research labs – environmental monitoring in high-elevation zones
If you operate a CO2 sensor module in a high-altitude environment, failing to account for barometric pressure differences can lead to significant reading errors. Whether through automatic pressure compensation or manual correction, adjusting for altitude is essential for accuracy.
If you need assistance choosing the correct sensor for your application email us or call us at (877) 678-4259. We'll be happy to answer any of your questions.
