Development of a Humidification System for Use in Field Studies of Air Pollution Effects on Crops

摘要

A humidity generation system was designed, constructed, and tested to increase relative humidity (RH) within open top field chambers under field conditions. The system consisted of a gas fired steam boiler capable of generating 450 kg of steam at 1.055 kg/sq cm pressure. A modulating valve, controlled by a humidity sensor, metered steam to the chambers. Alfalfa plants exposed to 0.20 ppm of ozone at high RH 7 hrs/day for 2 days had visible injury to more than 50 percent of the leaves and increased leaf crop. Chronic exposure of alfalfa to ambient ozone at elevated RH over three harvest periods, resulted in 40 percent visible injury in the first and second harvests, and increased stomatal conductance. At the third harvest, exposure to ozone with elevated RH reduced dry weight and increased defoliation.