Field intercomparison of measurement techniques for total NH 4+ and total NO 3− in ambient air

Abstract

Water-soluble nitrogen compounds play an important role in the acidification and eutrophication of our environment. The most abundant species are NH 3 and HNO 3 which both are present in gaseous and particulate forms. They can both be transported over long distances, especially in particulate form. In order to study this transport a network of stations in different countries has to be used. A prerequisite is of course that all laboratories involved use comparable measurement techniques. Another prerequisite is that the methods are so simple and inexpensive to use that a dense network can be established even at remote places. Several field experiments have been performed in which techniques to measure the gaseous and particulate forms separately are compared. However, they have not been very successful. In this study three techniques to measure the total (gaseous and particulate) concentrations of NH 4 + and NO 3 − were compared in field experiments. Comparison of measurements made by different laboratories in different countries using the same sampling technique at a given place yielded a relative standard deviation of 20% for total NH 4 + and 15% for total NO 3 −. The same relative standard deviations were obtained when different sampling techniques (denuder, total filter, filter pack) were compared.