THE DESIGN ARID TESTING OF A RELAXED EDDY ACCUMULATION SYSTEM

A flux measuring system has been developed based on relaxed eddy accum ulation (REA, or conditional sampling) methodology. The system uses sa mpling tubes packed with solid substrates to collect air samples for d etermining the average concentration of compounds of interest. It has been designed for measuring fluxes of various trace gas species by usi ng appropriate. solid substrates in the tubes. The chief advantages to this design are the following: (1) the placement of pump and flow con trol apparatus are located downstream of the sampling tubes to elimina te Sample heating and reduce contamination of the sample stream; (2) t he addition of a zero gas channel available to the sampling tubes impr oves the flow stability without diluting the sample; (3) the design pe rmits the use of multiple sample tube magazines to allow sequential ru ns without interruption; and (4) the; use of compact, easily transport able sampling tubes permits analyses to be conducted gt an off-site la boratory where analytical conditions a;re better controlled. The REA s ystem was tested by measuring water vapor flux under held conditions;a nd the resulting measurements are compared with those ma;de using a Bo wen ratio system. The two methods gave similar results with fluxes val ues that agreed within 12%, although the measurements from the REA sys tem were generally higher than those from the Bowen ratio method.