**How much oxygen does a houseplant give off in a day?**

It is impossible to work out an accurate figure, but we can try to find an approximation.

The maximum amount of photosynthesis quoted in by Salisbury and Ross (Plant Physiology 4th Ed 1992 ISBN 0–534–15162–0, Table 12-3 p 253) varies between 0.6 and 40 µmol CO_{2} fixed per square metre of leaf per second.

If we settle on an average for temperate zone deciduous trees and shrubs (eg Beech) of 6 µmol m^{-2} s^{-1} and assume that 1 mole of O_{2} is produced for every 1 mole of CO_{2} fixed.....

We can calculate 0.69g of O_{2} produced per m^{2} per hour. ( 6x10^{-6} x 32 x 60 x 60 to convert to g per hour. )

Better ....

If 1 mole of O_{2} occupies 22.4 litres (at normal temp and pressure) I calculate this to be about 500 ml O_{2} per square metre of leaf surface per hour. ( 6x10^{-6} x 22.4 x 1000 x 60 x 60 / 10000 ) or 0.05 ml per cm^{2} of leaf surface per hour.

Even if my maths is right, it will still be only a guesstimate as it will depend on lighting conditions and temperature and carbon dioxide concentration and the species of the plant as well as the condition of the plant! The table in Salisbury and Ross suggests it could be 1/10 that figure or 10 times that figure when considering healthy plants.

John Hewitson