The use of sorbent tubes and a semi-continuous emissions monitor for the determination of atmospheric total gaseous mercury in Pretoria, South Africa

Abstract

Semi-continuous emissions monitors (SCEM) are widely used for the determination of atmospheric mercury. These sophisticated instruments perform nearly real-time measurements of atmospheric mercury. However, their high cost and limited mobility do not make them suitable tools for field measurements. On the other hand actively pumped Hopcalite-type sorbent tubes, connected to a vacuum pump, can be deployed to sample air even at remote locations without the need for an instrument shelter. This is particularly important for developing countries where the cost of a dedicated mercury analyser may be prohibitive to its widespread use. Analysis of the mercury content of exposed sorbent tubes may be performed by cold vapour atomic absorption spectroscopy (CVAAS). The necessary instrumentation is versatile, not limited to the determination of mercury and is used in many laboratories. During a five month monitoring campaign in Pretoria, South Africa, weekly average atmospheric mercury concentration data were generated using an Opsis HG 200 SCEM. They were compared to results obtained by exposing Carulite C300 sorbent tubes to ambient air, followed by CVAAS analysis of the absorbed mercury. The average mercury concentration during four months of measurements with the Opsis analyser was 1.7 ± 1.9 ng m-3 mercury, while 1.6 ± 0.4 ng m-3 were determined by sorbent tube / CVAAS analysis.