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Title:
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The reaction between HNO3, H2SO4 and NaCl-particles
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Author(s):
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Published by:
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Publication date:
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ECN
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1997
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ECN report number:
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Document type:
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ECN-RX--97-009
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Article (scientific)
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Number of pages:
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25
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Published in: To be submitted for publication in the Journal of aerosol science (), , , Vol., p.-.
Abstract:
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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