Reef Chemistry Question of the Day #254 Carbon Dioxide Formation

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #254

Most of us know that the pH in a reef aquarium can be impacted by the carbon dioxide level in the air around the aquarium.

Suppose that you are an average 70 kg man (wish I was ) and you are alone, resting on your couch watching TV in your living room.

The room is 10 feet by 20 feet by 8 feet high.

Approximately how long would it take for the carbon dioxide level to double from a starting point of normal air (350 ppm CO2)?

A. 6 minutes
B. 66 minutes
C. 666 minutes
D. 6,666 minutes

Assume no air exchange from outside the room, or into your reef tank.
(as an aside, this doubling of CO2 could potentially drop your small aquarium pH by 0.3 units; do not use this result since it doesn't help answer the question)

Good luck!











































.

 

[MnFish1]

So the number of cubic feet in the room is 1600. X .035 = 56 cubic feet of co2 in the room. A person produces .6-1.7 cf of co2 depending on exertion etc so the answer closest is 66 minutes. B 56/.9cf/hr

 

[JimWelsh]

So, the number of cubic meters in the room is 45.3. 350 PPM of that is 0.016 cubic meters worth of CO2. The Engineering Toolbox says one person at rest generates 0.02 cubic meters of CO2 per hour (https://www.engineeringtoolbox.com/co2-persons-d_691.html). The 66 minutes answer is closest.

 

[Gareth elliott]

6 minutes, tv powered by coal furnace in the tv room [emoji23]

 

[Chuk]

Average respiration rate for someone that size at rest ~16 breaths per minute, the lung volume is ~500mL(.0005 m3), and the average CO2 concentration in exhaled breath is ~4% CO2 (according to google). Based on that in a sealed 45.3 m3 room I get the following equation Cf=Ci+(.0005m3/45.3m3*40,000ppm)*#breaths . Solving that for the number of breaths it would be take ~793 breaths to increase the conc to 700 ppm which is about 50 minutes. the closest answer is B 66 min.

 

[nhlives]

I'm always amazed as to how fast the PH goes up when we leave the house for a day. I normally use a CO2 scrubber with a shutoff controlled by the Apex to keep PH in the 8.2 range. When we leave, the PH shoots up to 8.4 even with the scrubber by-passed.

 

[MnFish1]

So the number of cubic feet in the room is 1600. X .035 = 56 cubic feet of co2 in the room. A person produces .6-1.7 cf of co2 depending on exertion etc so the answer closest is 66 minutes. B 56/.9cf/hr

What I posted is incorrect - but the answer is still B. Should have been 1600 CF x .00035 = 0.56 CF CO2 in room. A person produces 0.5 CF co2 at rest per hour - so 0.56 CF CO2 / 0.5 cf/hour = 1.12 hours or 67 minutes to double the CO2

 

[MnFish1]

Average respiration rate for someone that size at rest ~16 breaths per minute, the lung volume is ~500mL(.0005 m3), and the average CO2 concentration in exhaled breath is ~4% CO2 (according to google). Based on that in a sealed 45.3 m3 room I get the following equation Cf=Ci+(.0005m3/45.3m3*40,000ppm)*#breaths . Solving that for the number of breaths it would be take ~793 breaths to increase the conc to 700 ppm which is about 50 minutes. the closest answer is B 66 min.

Thats Good. Even better when you consider that the average breaths/min on some sites is 12 (793/12 = 66.08)...

 

[klp]

B also from experience using a CO2 meter.

 

[klp]

B also with experience using a CO2 meter. Builds up fast.

 

[Randy Holmes-Farley]

And as most folks pointed out, the answer is...

Approximately how long would it take for the carbon dioxide level to double from a starting point of normal air (350 ppm CO2)?

B. 66 minutes

I won't go into the details of how to figure it as several people did, but it's a bit surprising how fast it happens.

But if CO2 rises this fast, why aren't people's CO2 problems worse?

The main reasons is that houses are generally pretty leaky to outside air. Even tight homes have air turnover, and most spaces have several air turnovers per hour. So the CO2 level that results is a combination of the sources (breathing, gas stoves and ovens, etc.) and the sinks (air exchange).

Happy reefing!