A New Analyzer for Sulfuric Acid and Sulfur Aerosols in Ambient Air: Development And Measurements

Summary

A semi-continuous analyzer has been developed for simultaneous monitoring of ambient sulfuric acid and sulfur aerosols. Sulfur aerosol concentration is measured directly with a flame photometric detector. Sulfuric acid is first adsorbed and accumulated in a heated diffusion denuder. Subsequently it is released by increasing the temperature to 700°C and analyzed by the same detector. With a time resolution of 30 min. the detection limit of the analyzer amounts to 0.1 µg m^-3 for sulfuric acid and 1.0 µg m^-3 for sulfur aerosols (calculated as S0₄ ^2-). The automated and computer controlled analyzer was applied to a clean and highly polluted air region (Edelmannshof; Berlin West)) and a smog chamber. Sulfuric acid was detected only in winter, where it reached up to 2.7 µg m^-3 at Edelmannshof and up to 0.74 µg m^-3 in Berlin (West). Corresponding S0₂ concentrations were much lower at Edelmannshof. In summer the ratio of S0₄ ^2-/S0₂ was found to be 10 times higher at Edelmannshof than in Berlin (West). The photochemical experiments, which were carried out with α-pinene, S0₂, NO_x, 0₃, H₂0 and light in Teflon bags, showed good reproducibility. The relative humidity influenced greatly the composition of the formed sulfur aerosols. More than 90% of these aerosols were identified as S0₄ ^2- using ion chromatographic analysis. Up to 50% of the converted S0₂ were recovered as suspended aerosols in the bag.