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FP5

THALOZ Report Summary

Project ID: EVK2-CT-2001-00104
Funded under: FP5-EESD
Country: United Kingdom

Model simulation: active chlorine release from marine aerosols: roles for reactive iodine and nitrogen species

A simulation of marine boundary layer chemistry has been carried out in order to investigate chlorine atom release from marine aerosols. Measurements of iodine oxide (IO) and nitrate (NO3) radicals from field experiments were used to constrain model simulations. The results of these calculations show that the uptake of both HOI and N2O5 in the marine boundary layer has the potential to liberate chlorine atoms from sea-salt aerosol at a significant rate.

Simulations show that a burst of chlorine production should be expected at sunrise due to photolysis of ICl formed overnight from HOI and Cl-. During the rest of the day, calculations show chlorine production to be steady, leading to steady state concentrations of Cl in the range of several hundred to a few thousand / cc, in accordance with some field studies. Chlorine atoms concentrations of a magnitude (10,000atoms /cc) capable of significantly influencing the oxidation potential of the atmosphere (for gases that are normally expected to react with OH e.g. methane, ethane and DMS) could be sustained by iodine-catalysed release alone. The production of chlorine is complex and depends upon the relative abundance of NOx and HOx chemistry and the abundance and mixing state of the aerosol.

These results have been disseminated in the scientific press and are likely to provoke further research. The work may also prove to be of use in future field experiments e.g. the burst of chlorine at sunrise could be used as a diagnostic for this mechanism in future field experiments.

Citation: McFiggans G, R.A. Cox, J.C. Mossinger, B.J. Allan and J.M.C. Plane, Active chlorine release from marine aerosols: Roles for reactive iodine and nitrogen species, J. Geophys. Res. 107 (D15) art. no. 4271, 2002.

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