# Plants producing Oxygen at Night

Carsten Richter carsten.richter at rz.hu-berlin.de
Wed Oct 25 15:15:55 EST 2000

```> Dear Carsten,
> I believe it is not a matter of producing oxygen, but of consuming oxygen
> by respiration. Let us assume that the respiration rate in the dark is 40%
> of the photosynthesis rate in the light. You can use your figures to
> calculate oxygen deficit due to plants which it must be added to the
> oxygen deficit produced by humans (in an inhabited room). This will
> reduce the O2 concentration,l and increase the CO2 cincentration in the
> gas-tight room with the end effect a feeling of discomfort by the humans.
> Right or wrong?
> Regards, George
>

Hello George,

I would agree that the production of CO2 is a much bigger problem than
production/consumption of oxygen.

Some more calculations:
Assumptions:

10m2 leaf area
60m3 room
30 mg*dm-2*h-1 photosynthetic rate
12 mg*h-1 respiration rate (although I think 40% is too much, better 10-20%
?)
production of CO2/consumption of O2 by human: 230 ml*h-1
normal CO2-concentration: 350 ppm, room contains 21 liter CO2
normal oxygen-concentration: 21%, room contains 12600 liter O2

Change of concentrations after 12h:

Light on

Plants alone:
Production of 182.4 liter oxygen, O2 concentration: 21.3%
Consumption of 182.4 liter CO2, CO2 concentration :  below 0% (uups, we have
a little problem here with our gastight room, maybe we should open a window,
at least for a short time :-) )

Human alone:
Consumption of 165.6 liter O2, O2 conc. 20.7%
Production of 165.6 liter CO2, CO2 conc. 0.311 % (3110 ppm)

Light out

Plants alone:
Production of 73 liter CO2, CO2 concentration: 0.1566% (1566 ppm)
Consumption of 73 liter O2, O2 concentration :  20.9

Human alone (same as above):
Consumption of 165.6 liter O2, O2 conc. 20.7%
Production of 165.6 liter CO2, CO2 conc. 0.311 % (3110 ppm)

During the 12 h without light the production of CO2 by the plants and one
human (calm, not working) would not reach a level of 5000 ppm. In Germany we
have the so called MAK-values for certain substances. For CO2 it is 5000
ppm, that means concentrations below this value are believed to be harmless.
So far we have no problem in our gastight room.

for clean and healthy air with harmless CO2 concentrations: remove any