A THERMOANALYTICAL APPROACH TO SPECIATION OF ATMOSPHERIC STRONG ACIDS

A thermoanalytic device for the selective determination of atmospheric sulfuric acid, called a thermo-denuder, is described. The acid droplets are thermally decomposed in a heated glass tube and the small fragments formed are collected at the walls of the tube by diffusion-controlled deposition. High sampling efficiency is achieved when the inner wall of the glass tube is coated with sodium chloride as a trapping agent. Sulfate and bisulfate salt particles pass through the tube unaffected and can be collected on a back-up filter. After the sampling the tube is rinsed with water and the dissolved coating analyzed for sulfate using isotope dilution analysis. Applying a nitrate-specific method to the analysis of the extract, the sum of nitric acid and ammonium nitrate can also be determined by the thermo-denuder technique.