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Humidity is an important component of the enviornment that influences the growth, development and storage life of most horticultural crops. A method to control relative humidity (RH) in experimental chambers using solutions of glycerol-water has been developed. A constant RH can be established and maintained by bubbling air through a glycerol-water solution of known water content. The air rapidly reaches equilibrium with the glycerol-water solution producing the desired RH. The relationship of the specific gravity (SG) of glycerol-water solutions and the corresponding equilibrium RH was determined. Any desired RH can be produced by using solutions of the appropriate SG ranging from 100% with pure water (SG 25/25 = 1.000) to 0% with pure glycerol (SG 25/25 = 1.261) This system can be used in flow through systems by bubbling the incoming air through the solution or in closed systems by circulating air through the solution and the chamber. Multiple jars of solution can be used for more precise RH control. The effects that temperature and atmospheric pressure in the jars have on the equilibrium RH will be discussed.
Solutions of glycerol and water provide a convenient and inexpensive system to control the relative humidity (RH) in small controlled-environment chambers. The relationship between the specific gravity (SG) of a glycerol-water solution and its equilibrium RH is described by the equation SG = [-0.189 (RH) + 19.9]0.0806. Gas can be humidified by bubbling it through jars containing solutions of glycerol-water with the desired equilibrium RH. The effects of flow rate, volume of solution, temperature, and pressure on the equilibrium RH are discussed.
Refrigerated (2 °C) controlled atmospheres significantly increased the mortality of green peach aphids [Myzus persicae (Sulzer)] and western flower thrips [Frankliniella occidentalis (Pergande)] in laboratory experiments. However, insect mortality during marine shipment in mixedload containers at 0.5 °C did not significantly increase in a controlled atmosphere. In laboratory experiments, mortality of green peach aphids ranged from 32.8% in the refrigerated control to 96.8% after storage in 0.10% O2 for 4 d followed by 7 d in 3% O2 with 5% CO2. When stored under these same conditions, western flower thrips mortality was 71% compared to 16% mortality in the refrigerated control. Following an 11-day marine shipment from California to Guam in a controlled atmosphere, vase life was extended for most of the 20 California cut-flower and foliage products compared to those shipped in the refrigerated air control.