Evaluatie van bepalingen van natrium- en kaliumconcentraties in extracten afkomstig van monsternemingen met Annular Denuder Systemen

Abstract

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A number of samples from measurements with an Annular Denuder System (ADS), performed within the framework of the project "atmospheric acidity", have been analysed on Na+ and K+. These analyses have been done apart from the determinations of sulphate, sulfite, nitrate, nitrite, ammonium, chloride and hydronium concentrations in the samples usually done in this project. Concentrations of Na+ and K+ have also been determined in samples of uncoated denuders and in samples of the deionized, distilled water used for extraction of the ADS denuders and filters. The results show that no Na+ is captured in the denuders during air sampling, implying that no deposition of particles in the denuders occurs during this process, in agreement with what should be expected. On the teflon filters, used to collect the particles after they have passed the denuders, only small concentrations of Na+ and very small concentrations of K+ were found. Seasalt aerosol is probably the main source of Na+. For 15 samples of teflon filters the cation/anion ratio was calculated. This ratio varies from 0.9 to 1.1 indicating that the ions determined in this examination form the most important "charged" components in small aerosol particles (diameter < 2.5 mum). If only the concentrations of nitrate, sulphate, ammonium and hydronium are taken into account the cation/anion ratio still does not differ much from 1, except of these concentrations are very small. This fact can be used for the validation of analyses of all teflon filter samples in the "atmospheric acidity" project, which are normally only analysed on these four ions. In a similar way measurements of concentrations of sulphate, nitrate, ammonium and chloride, performed with fitlerpacks within the Dutch Air Quality Monitoring Network, can be validated.