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Abstract.Monthly dustfall samples collected in 16 sites in the Tel-Aviv urban areas, as well as those collected in 10 rural sites in Israel during several years of measurements, were analyzed for their physical properties and chemical content. Although dustfall measurements represent a very simple and crude technique the analysis of the data provides some very interesting conclusions:(a) The southwest part of Israel, which is scarcely populated, suffers from high dustfall values due to dust storm blowing from the Sahara and other arid lands to the east Mediterranean during the spring.(b) On an annua[ basis the natural dustfall of dust storms origin amounts to 25 to 30% of the Tel-Aviv residential area deposition or 3 to 4 tonne km--" mo-t.(c) Mapping ofdustfall data within an urban region reflects fairly well the main industrial and commercial activities within the city.(d) In residential areas the inorganic water insoluble fraction of the dust is contributed by natural sources, while the organic fraction is mostly of anthropogenic origin. The inorganic water soluble fraction is spread in a uniform pattern within the city.

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A method involving the use of a reagent suitable for the rapid spectrophotometric determination of nitrites in water is described. Nitrites react with resorcinol in an acidic medium and the nitroso product forms a pale yellow chelate with the zirconyl ion. The absorbance of the chelate is measured a t 347 nm and the calculated molar absorptivity is 2.67 x lo4 1 mol-l cm-l. The method is suitable for the determination of the nitrite ion in a 1.0-cm cell in the range from a few parts per hundred million to about 1 p.p.m. The relative standard deviation of the method is 1.5% a t a concentration of 1 p.p.m. Some of the problematic interferents found in most of the analytical procedures for the determination of nitrites are tolerated in the present method. Features of the method include good selectivity and reproducibility, high stability of the coloured reaction product and simplicity.Keywords : Spectrophotornetry ; nitrite micro-determination ; water ; chelation ; zirconyl i o nNitrite, when correlated with other nitrogen forms in water, can provide an index of organic pollution and oxides of nitrogen in the air are well known health hazards. General reviews dealing with the determination of nitrite can be found in the literat~re.l-~ The most widely used and applied methods are those based on spectrophotometry, and they can be classified into four main groups : group 1, diazotisation of an aromatic amine and subsequent coupling to form an azo dye; group 2, oxidation of an organic molecule by nitrite; group 3, formation of free radical chromogens; and group 4, formation of nitroso compounds.In the group 1 methods, a naphthalene derivative is usually used as the coupling agent. The original method of Griess4 was modified several times ; one of these modifications by Rider and Mellons was adopted by the ASTM Committee and has became a standard procedure.6 The GABBAY et al. : RAPID SPECTROPHOTOMETRIC