Sometimes I want to be able remove the lid from a sealed bottle to attach a CO2 sensor, then put the lid back on afterwards. How much CO2 is lost from the bottle when I do this?
I performed the experiment as follows:
- CO2 level in the room at the start of the experiment was measured as 400ppm
- Temperature in the room at the start of the experiment was measured as 16.1C
- Breathed into 600ml bottle to raise CO2 level.
- Left sensor attached to bottle for 1 hour (to make sure the reading had stabilised)
- Removed sensor for approximately 10 seconds, then reattached. Removal and reattachment involve screwing and unscrewing. 10 seconds was the duration of the period when the opening of the bottle was unobscured by the sensor and open to the air in the room.
- Left the sensor attached until the reading was stable again.
- Temperature in the room at the end of the experiment was 16.3C
- CO2 level in the room at the end of the experiment was still 400ppm.
The CO2 level measured at the end of step 4, before exposing the bottle to open air, was 9600ppm. At the end of step 6 the reading was 9100ppm.
I believe that 10 seconds is longer than the total time that the bottle opening is exposed to the air when I normally attach then later remove the CO2 sensor. In most of the experiments I’m doing, the volume of air in the bottle is probably between 300ml and 400ml, the CO2 level in the bottle is generally less than 10000ppm, and the CO2 level in the room is between 400ppm and 1300ppm. So I think I lose 5-10% of the CO2 in the bottle when I attach and remove the sensor.