Converting CO2 measurement from the ISS

When referring to the ISS telemetry data, you may have noticed that the carbon dioxide data is recorded as a partial pressure in millimetres of mercury (mmHg). Yet, we coded our micro:bit – CozIR  sensor device to record carbon dioxide values in parts per million (ppm).

This is due to the different measurement methods used. The micro:bit – CozIR  sensor device has a non-dispersive infrared (NDIR) gas sensor, which uses a beam of infrared light to measure the concentration of carbon dioxide in the sample chamber. For the ISS telemetry data, carbon dioxide is measured using a mercury-filled, u-shaped tube. The mercury rises in the tube in response to the downward force from the carbon dioxide (or other gas). Some astronauts also wear personal carbon dioxide sensors (custom board with CozIR sensor) to detect the formation of harmful pockets of carbon dioxide around the astronaut's head.

Students will need to convert ISS telemetry carbon dioxide values from a partial pressure (mmHg) to parts per million (ppm). To see an example, make sure that you are logged in to LetsTalkScience.ca as an educator, THEN go to this link: http://explorecuriocity.org/lsap/#/EducatorAction1/1.1

Click on STEP 3 and then make sure you “Click to Expand Student View” to view the unit conversion example.

IF you want a quick shortcut for situations where you do not want to get students to do the long formula for calculations, simply get them to multiply the CO2 mmHg readings from the ISS by 1315.79 ( 1.0 mmHg = 1315.79 ppm) Ex: An ISS reading of 2.90 mmHg CO2 multiplied by 1315.79 = 3,815.79 ppm CO2.

Important Links explaining high levels of CO2 on the ISS: High CO2 Levels on the ISS