Comparison study on portable wind tunnel system and isolation chamber for determination of VOCs from areal sources

Many environmental monitoring programmes require the determination of volatile organic compounds (VOCs) emitted from large areal sources including liquid surfaces. A study was carried out to compare existing sampling techniques. Both the isolation chamber method (static technique) and the wind tunnel method (dynamic technique) were examined. A review of the mechanisms suggested that static techniques would not be appropriate for determining emissions from liquid surfaces which result from gas phase controlled volatilisation processes. A portable wind tunnel developed at the University of New South Wales and an isolation chamber built to USEPA specification were used in an experimental study of emissions from aqueous liquid surfaces. An acetone solution was chosen to represent gas phase controlled volatilisation processes. Toluene and methyl ethyl ketone in aqueous solution were chosen, respectively to investigate (1) liquid phase controlled volatilisation processes, and (2) combined gas and liquid phase controlled volatilisation processes. It was found that the use of the isolation chamber method resulted in different degrees of underestimation of the emission rates for the above three compounds. The wind tunnel method is suitable for sampling all VOC emissions from areal sources.