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| Titel |
The Spatial Distribution of IOx and impacts upon HOx and NOx at a Coastal Site |
| VerfasserIn |
W. J. Bloss, L. J. Concannon, R. Commane, C. S. E. Bale, T. Ingham, D. E. Heard |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024278
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| Zusammenfassung |
| The release of iodine compounds into the marine atmosphere can affect a number of
aspects of atmospheric composition: Iodine species can participate in catalytic ozone
destruction cycles, which may be augmented by bromine species; reactions of iodine
compounds can perturb the OH:HO2 and NO:NO2 ratios, heterogeneous loss of
reservoir compounds such as HOI and IONO2 can lead to removal of HOx and NOx,
and higher iodine oxides can contribute to the formation and/or growth of aerosol
particles. Several recent field campaigns have investigated the impact of iodine
chemistry upon atmospheric composition, at both coastal sites (e.g. Mace Head,
Roscoff) and open ocean locations (e.g. Cape Verde). In this work, we focus upon
understanding the effect of the spatial distribution of iodine emissions upon HOx and NOx
levels at coastal sites, using new observations to re-evaluate previous field campaign
data.
We present an analysis of results from two new instruments which measure point
inorganic iodine species concentrations: A laser induced fluorescence (LIF) instrument for
the detection of IO radicals, and a resonance fluorescence (RF) system for the detection
of iodine atoms, and the total photolabile iodine content. Both instruments were
deployed at Mace Head, Ireland during July-August 2007, during which period
point measurements of IO (up to 34 ppt), I (up to 20 ppt) and total photolabile
iodine content (up to 180 ppt I2 equivalent; nighttime) were made at the shoreline
site.
A detailed photochemical box model is employed in a lagrangian sense to simulate the
evolving chemical composition resulting from the emission of significant amounts of
molecular iodine from the intertidal zone exposed at low tide. The modelled inorganic iodine
species (I2, I, IO) are consistent with the levels measured by the LIF and RF systems. The
model is used to explore the transient response of the NOx and HOx families at the Mace
Head site to heterogeneous iodine emissions: The transit time between the intertidal iodine
emission zone and the shoreline site where previous measurements of HOx, NOx etc. have
been made (for example, during the NAMBLEX and ACSOE campaigns) is insufficient
for steady-state to become established, although this assumption has been made
in earlier model studies of such data. In this work, the model is used to explore
the short-term perturbation of the HOx and NOx radical chemistry by the iodine
emissions, considering the envelope of typical chemical and meteorological conditions
encountered at Mace Head. The limitations arising from uncertainties in the iodine
kinetics and photochemistry are quantified, and implications of the results for the
interpretation of observations of HOx and NOx in similar coastal locations considered. |
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