Application of a Thermo-Denuder Analyser to the Determination of H2SO4, HNO3and NH3in Air

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Abstract
The thermoanalytical method for speciation of atmospheric strong acids developed by Nieher and Klockow has been extended to the measurement of the HNO3/H2SO4/NH3 system in air. A series of coated tubes operated at different temperatures are used to collect selectively nitrate-and sulphate-containing atmospheric trace compounds as well as free ammonia. HNO3 and NH3 are collected at room temperature by NaF-and H3PO4-coated tubes, respectively. H2SO4 and HNO3 resulting from the dissociation of NH4NO3 are collected by the NaF coating of a denuder tube heated to 39-410 K. The liberated NH3 (from NH4NO3) is deposited in a subsequent H3PO4-coated tube. At 490-510 K ammonium sulphates decompose forming H2SO4 and NH3. The fragments are trapped in the same way using tubes with a NaF and a H3PO4 layer, respectively. All tubes are washed out with water. In the extracts NO3 − and SO4 2- are determined by ion-chromatography, NH4 + by means of an ion-selective electrode.