MONITORING SO2 WITH PASSIVE SAMPLERS - A LABORATORY EVALUATION OF NA2CO3 AND TRIETHANOLAMINE AS ABSORBING MEDIA

Two different types of passive samplers (a badge and a tube-type) for the determination of SO2 have been developed. Both samplers make use of a Na2CO3 coated quartz fiber filter as sampling layer. SO2 is collected as sulfite which, after extraction and oxidation, is determined as sulfate using ion-chromatography. In laboratory calibration tests good linearity of the average uptake has been found over a SO2 concentration range from 20 to 400 ppb. The sensitivity and capacity of the method is sufficient to cover a wide range of ambient concentrations, while the badge and the tube have detection limits for a one week exposure of about 4 and 34 mu g/m3 respectively. Precision, calculated on replicates, for both samplers was found to be between 5 and 10%. The influence of humidity was studied in comparison to triethanolamine (TEA) coated substrates. It was seen that for the collection efficiency TEA coated filters show a 2 to 3 times stronger dependency on relative humidity in comparison to Na2CO3. It was also found that the badge type sampler showed good performance with an average windspeed higher than 1 m/s. The tube sampler was found to give reliable and accurate results at windspeeds lower than 1 m/s. Accuracy was investigated in the field in comparison with a diffusion denuder technique. Regression analysis of the data indicated good agreement between the two methods.