AIR QUALITY IN GREENHOUSES WITH AND WITHOUT CO₂ ENRICHMENT

Because of the increased costs of heating, Dutch growers have insulated their greenhouses more and more. When CO₂ enrichment takes place this results in an increase of the concentrations of NO and NO₂, and possibly of unsaturated hydrocarbons if the combustion is not complete. A study has been started to investigate the consequences of these elevated levels on air quality and crop production. First measurements have been made of the air composition inside and outside two glasshouse compartments at the Glasshouse Crops Research and Experiment Station, Naaldwijk. During winter months the daily NO concentrations passed phytotoxic levels (250 ppb). Because of the vicinity of the large industrial area Europoort and the large cities of Rotterdam, Delft and The Hague, there is a relatively high level of NO_x, O₃ and SO₂ in the air in the South Holland Glasshouse District. In addition to the elevated NO_x levels from CO₂ enrichment crops may also be exposed to gaseous air pollutants from outdoors by influx through open ventilators. Situations with regard to air composition during periods with and without CO₂ enrichment, and closed and opened ventilators are described and illustrated.