Tools for Measuring Ethylene Gas in the Greenhouse 



BY SUSAN S. HAN 



Department of Plant and Soil Sciences 



University of Massachusetts 



Amherst, MA 01003 



Ethylene has long been associ- 

 ated with abortion, abscission, 

 and premature death of leaves, 

 buds and flowers of many plant spe- 

 cies. Depending on the plant spe- 

 cies, some flowers are very sensitive 

 to ethylene and concentrations as 

 low as parts per billion (ppb) can 

 induce senescence. Other species are 

 less sensitive to ethylene and may 

 display either no symptoms or only 

 have subtle changes in growth. Eth- 

 ylene (C,H^) itself is a very small, 

 gaseous compound that penetrates 

 readily into any air space. Most 

 greenhouse growers are aware of the 

 potential damage from ethylene pol- 

 lution in the greenhouse. In most 

 cases, the source of the ethylene is a 

 result of improperly installed heaters 

 or from inefficient and defective 

 units. Despite the precautions taken 

 by growers to maintain and inspect 

 the heaters regularly, it is not un- 

 common to have reports of crop 

 loss due to ethylene pollution, espe- 

 cially in the Northeast where heaters 

 are heavily depended upon for 

 growing crops in the winter. 



A gas chromatograph is the most 

 widely recognized device for the 

 precise measurement of ethylene. It 

 is an expensive piece of equipment 

 that requires regular maintenance 

 and skilled technicians to operate 

 and is thus generally used in 

 academia or commercial research 

 laboratories for detection of C,H, 



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concentrations. The current practice 

 in the industry is to send gas 

 samples from greenhouses suspected 

 of ethylene pollution to an analyti- 

 cal laboratory which then uses a gas 

 chromatograph to measure the ethyl- 

 ene concentration. Results from gas 

 chromatography are dependable but 

 the costs for the analyses are high. 



In addition, this entire process usu- 

 ally takes a few days, a time period 

 during which the entire crop may 

 be destroyed. 



In the past, I have received gas 

 samples from commercial green- 

 houses in the New England area 

 containing very high levels of ethyl- 

 ene, usually due to faulty furnaces. 

 Typically by the time gas samples 

 are sent for analysis, crop damage is 

 substantial. With the sharp increase 

 in energy costs, growers are 

 prompted to plug small air holes in 

 the greenhouse in order to reduce 

 heating bills. These holes are vital 

 for venting away any ethylene that 

 might exist in the greenhouse and, 

 when plugged, greatly increase the 

 risk of ethylene damage to the crop. 

 It is, therefore, critical that green- 

 house growers monitor ethylene 

 concentration in the greenhouse 

 each year when first firing up the 

 heater and on a regular basis during 

 the crop production period. 



In 2002, the New Hampshire 

 Plant Growers' Association funded a 

 research project in my laboratory to 

 investigate the accuracy of a simple 

 and inexpensive device for measur- 

 ing ethylene in the atmosphere. The 

 device from GASTEC^^ is designed 

 to provide instant readings of ethyl- 

 ene concentration from 100 to 400- 

 ml gas samples. This method is in 

 contrast to the 1-ml samples typi- 

 cally injected into the gas chromato- 

 graph. The GASTECT^ ethylene de- 

 tector device works like a syringe. It 

 has a plunger to pull air in and the 

 tip of the device is connected to an 

 ethylene detector tube (Fig. 1). Ac- 

 cording to the manufacturer, the 

 tubes are constructed to detect eth- 

 ylene concentrations in the range of 

 0.2 ppm to 800 ppm. There are 



two types of tubes, one for the 

 lower range of 0.2 ppm to 50 ppm 

 and the other one for the higher 

 range of 50 ppm to 800 ppm. The 

 device is designed to draw in 100 

 ml of gas with each sampling and 

 four withdrawals are required for 

 the lower range tubes. For the 

 higher range tubes, one gas sam- 

 pling of 100 ml is sufficient. The 

 detector tubes are disposable and 

 can only be used once. Each tube 

 has a calibrated scale printed on the 

 outer surface and the degree of 

 color changes inside the tube (from 

 light cream color to blue), due to 

 interaction of (NH^),MoO^ and 

 PdSO^ with ethylene gas to produce 

 molybdenum blue, indicates the 

 concentration of ethylene in the at- 

 mosphere. Each drawing of the 100- 

 ml sample takes 2 minutes. There- 

 fore, eight minutes (four samplings) 

 is required for the sampling process 

 in the low range tubes. For the high 

 range tubes, only two minutes is re- 

 quired. The color change is sponta- 

 neous, therefore, giving growers in- 

 stant readings of the ethylene level 

 in the greenhouse. If the device 

 proves accurate and produces consis- 

 tent results, it would be a very use- 

 ful tool for a quick check of the 

 ethylene concentration in the green- 

 house and, thus, greatly reduce the 

 risk of losing the entire crop due to 

 ethylene gas. 



In order to determine the accu- 

 racy and dependability of the 

 GASTEC^^ for measuring ethylene 

 gas in the greenhouse, we compared 

 the ethylene readings from the 

 GASTEC^''^ device to those of the 

 Shimadzu 9A gas chromatograph in 

 my laboratory. A series of experi- 

 ments were conducted where ethyl- 

 ene concentrations ranging from 0.1 



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The I'lanlsman 



