IMPROVEMENT OF THE TETRACHLOROMERCURATE ABSORPTION TECHNIQUE FOR MEASURING LOW ATMOSPHERIC SO2 MIXING RATIOS

During the Gas-Phase Sulfur Intercomparison Experiment (GASIE) in 1994 an analytical system for measuring sulfur dioxide mixing ratios at lo w parts per trillion (pptv) levels was employed. It is based on the ab sorption of SO2 on a tetrachloromercurate(II)-impregnated filter. The subsequent analysis uses a chemiluminescence reaction by treating the resulting disulfitomercurate(II) complex with an acidic cerium sulfate solution. An improved sampling device has been introduced that increa ses the maximum sampling volume from 200 L to 500 L. It is also possib le to determine the blank value accurately for each sample. The absorp tion efficiency of the sampling system is 98.7 +/- 6.4% at a nominal f low rate of 10 L/min. The calculated (3 sigma) detection limit is 3 +/ - 1 pptv SO2. The sample solution is stable for up to 30 days, which a llows the samples to be safely stored or shipped before analysis. This permits the use of a sensitive, compact, and reliable sampling system in the field with subsequent analysis under optimal conditions in the laboratory. A continuous flow chemiluminescence (CFCL) analyzer fbr o n-line measurements is also presented. The system is based on the same chemical principles as the described filter technique.