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| Titel |
A global inorganic source of reactive iodine to the marine lower atmosphere: field observations and laboratory studies |
| VerfasserIn |
Juan Carlos Gomez Martin, Samantha MacDonald, Anoop Mahajan, Alfonso Saiz-Lopez, Rosie Chance, Lucy Carpenter, John Plane |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076015
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| Zusammenfassung |
| Reactive iodine (IOx = I + IO) in the marine boundary layer (MBL) can have a significant
impact on the lifetime of oxidising species, by causing ozone destruction and changing the
HOx and NOx partitioning, and can also contribute to new particle formation. Interest in
measuring IOx species in situ across the Pacific Ocean has been driven in the last few years
by satellite observations of enhanced iodine monoxide (IO) column densities over the Pacific
‘cold tongue’ (Schönhardt et al., 2008), which suggested potential links between biogenic
ocean emissions and climatically relevant atmospheric chemistry. Spatially and time-resolved
MAX-DOAS and LP-DOAS observations of IO in the Pacific MBL have been reported very
recently (Mahajan et al. 2012, Groβman et al. 2012, Gómez Martín et al., 2013), indicating
a constant and ubiquitous presence of IOx. The IO mixing ratios in the Pacific
are similar in variability and magnitude to those observed in other remote tropical
locations, although generally lower. However, satellite observations of IO above the
Pacific appear to be inconsistent with its surface spatial distribution and low mixing
ratios.
In this paper we present new insights into the global oceanic source of reactive iodine,
obtained by analysing correlations between different oceanic variables and IOx and from new
laboratory measurements where such variables are changed in a controlled manner. Similar to
previous studies in the Atlantic Ocean (Mahajan et al., 2010, Jones et al., 2010), halocarbons
cannot fully account for the IOx observed in the Pacific. Moreover, enhanced IO mixing
ratios are found over the oligotrophic parts of the ocean and during the warm season. Positive
correlation of IOx with sea surface temperature, salinity and iodide, and negative
correlation with Chl-a, point to a ubiquitous inorganic iodine source. Deposition of
O3 to the sea surface and subsequent reaction with iodide in the interfacial layer,
resulting in the release of both I2 and HOI into the gas phase, is the most plausible
explanation.
Laboratory experiments have been carried out to quantify and characterise the flux of
inorganic iodine precursors produced from this process, as a function of temperature, iodide
concentration, ozone concentration, salinity, turbulence and organic species. The I2/HOI
relative yield has been investigated by selective laser and broad band photolysis, and it has
been found that HOI is the major iodine precursor under open ocean conditions. A kinetic
model of the interfacial layer of the sea surface has been used to model the laboratory results,
from which a parameterised function of the iodine flux has been derived. MBL 1 D modelling
using this source function generates IO concentrations in agreement with observations
(Carpenter et al., 2013). |
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