THE MEASUREMENT AND CONTROL OF CARBON DIOXIDE CONCENTRATION
The technique of carbon dioxide enrichment is now practised by many growers and hence there is much interest in suitable methods of measurement and control of carbon dioxide concentration. Several sources of carbon dioxide for enrichment are available. Pure carbon dioxide, costing up to 6d per lb, may be obtained from cylinders, liquefiers or in solid form. At a cost of about 3d per lb, carbon dioxide may be produced by burning bottled gas (propane). The cheapest source of all, costing roughly 1d per lb, is the combustion of paraffin. Many grades of paraffin contain sufficient sulphur, when burnt without adequate control, to constitute a hazard to glasshouse crops. Thus the need for measurement and preferably automatic control of carbon dioxide concentration exists, either for reasons of economy in the use of relatively expensive pure carbon dioxide, of to prevent the possibility of phytotoxic concentrations of sulphur dioxide if it is desired to use the cheapest source of carbon dioxide.
The carbon dioxide concentration in the atmosphere is normally about 0.03% by volume, or 300 vpm. The abbreviation vpm. stands for volumes per million volumes of air.
Bowman, G.E. (1968). THE MEASUREMENT AND CONTROL OF CARBON DIOXIDE CONCENTRATION. Acta Hortic. 7, 81-87