Iodine Chemistry in the Marine Boundary Layer

Iodine compounds - alkyl iodides such as CH2I2 and molecular iodine, I2 - are released to the atmosphere from exposed seaweeds in coastal areas, and through biological activity in the open ocean. They undergo solar photolysis on timescales of seconds to minutes, releasing their constituent iodine atoms, which react with ambient ozone to form IO radicals. Subsequent reactions of IO can lead to ozone destruction, affect the OH:HO2 and NO:NO2 ratios in the MBL (marine boundary layer), and lead to the formation of new particles, which may in turn act as CCN (cloud condensation nuclei) potentially affecting weather and climate. In order to quantify these effects, we need to know the concentrations and distribution of iodine species, and to understand the details of kinetic and photochemical reactions involved. Our research aims to address some of these key uncertainties in the atmospheric iodine cycle.

Laminaria, a source of alkyl iodides

A new instrument has been developed to measure halogen atom concentrations in the MBL, using resonance fluorescence. A resonance lamp produces VUV radiation uniquely characteristic (through the electronic energy level structure) of the element under consideration. This radiation is directed onto ambient air, sampled into a reduced pressure cell, causing any atoms to fluoresce; detection of the resulting fluorescence allows the halogen atom concentration to be obtained. A prototype of the instrument (below) has recently been tested at Mace Head, Ireland during summer 2007. This work was carried out by Dr Catherine Bale, funded by NERC.

Novel Measurements of Atmospheric Iodine Species by Resonance Fluorescence
C.S.E. Bale, T. Ingham, R. Commane, D.E. Heard and W.J. Bloss
J. Atmos. Chem. 60, 51-70, 2008

Prototype RF System

Under development in the laboratory
Mace Head, Aug 2007

Deployed at Mace Head, August 2007

Supported through a new NERC research grant, Dr Juan Najera is currently refining the prototype instrument, and extending the measurement capability to include bromine species. We plan to deploy the system in coastal and open ocean environments in 2010/11.

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