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ECN publication
The reaction between HNO3, H2SO4 and NaCl-particles
Published by: Publication date:
ECN 1997
ECN report number: Document type:
ECN-RX--97-009 Article (scientific)
Number of pages:

Published in: To be submitted for publication in the Journal of aerosol science (), , , Vol., p.-.

Kinetic information on the substitution of seasalt chloride by nitratewas deduced from a smog chamber investigation on the reaction of airborne NaCl with HNO3. It was found that a measurable reaction only occurred when the NaCl-particles were present in the form of droplets. The substitution of chloride by nitrate was independent of size which shows that the generation of the product (HCl gas) was the rate limiting reaction step. The rate of this reaction was more than one order of magnitude slower than the rate at which nitric acid can reach the droplets. The substitution of chloride by sulphate, in a reaction between H2SO4 and NaCl, depended on particle size; from this it was concluded that the transport of H2SO4 to the aerosol was the rate-limiting process. The difference in reaction of the two acids is explained by the fact that sulphuric acid is a condensable species, whereas nitric acid is a gas. From the amount of sulphate as a function of size an uptake coefficient for the condensing sulphuric acid was deduced of 0.1 or higher. The present study of the substitution of seasalt chloride by photochemically formed nitric acid and sulphuric acid has special relevance for the 'satellite' retrieval of marine aerosols, because this occurs with cloudless skies, which is a situation when photo-oxidation processes proceed at their maximum rate. The satellite retrieval uses the reflection of solar light by the aerosols and the reflective properties of seasalt to translate the reflection to aerosol loading. The substitution of seasalt chloride by sulphate and nitrate changes the optical properties of the seasalt which should be considered in the evaluation of retrieval data in regions where this substitution occurs. The present study contains kinetic information for modelling the extent of the substitution in such environments. 4 figs., 1 tab., 13 refs.

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