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Martin J.C.G.,Laboratory for Atmospheric and Climate Science CIAC | Martin J.C.G.,University of Leeds | Mahajan A.S.,Laboratory for Atmospheric and Climate Science CIAC | Mahajan A.S.,Indian Institute of Tropical Meteorology | And 14 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

Observations of gas-phase iodine species were made during a field campaign in the eastern Pacific marine boundary layer (MBL). The Climate and Halogen Reactivity Tropical Experiment (CHARLEX) in the Galápagos Islands, running from September 2010 to present, is the first long-term ground-based study of trace gases in this region. Observations of gas-phase iodine species were made using long-path differential optical absorption spectroscopy (LP-DOAS), multi-axis DOAS (MAX-DOAS), and resonance and off-resonance fluorescence by lamp excitation (ROFLEX). These measurements were supported by ancillary measurements of ozone, nitrogen oxides, and meteorological variables. Selective halocarbon and ultrafine aerosol concentration measurements were also made. MAX-DOAS observations of iodine monoxide (IO) display a weak seasonal variation. The maximum differential slant column density was 3.81013 molecule cm-2 (detection limit ∼7×1012 molecule cm-2). The seasonal variation of reactive iodine IOx (= I + IO) is stronger, peaking at 1.6 pptv during the warm season (February-April). This suggests a dependence of the iodine sources on the annual cycle in sea surface temperature, although perturbations by changes in ocean surface iodide concentration and solar radiation are also possible. An observed negative correlation of IOxwith chlorophyll-a indicates a predominance of abiotic sources. The low IO mixing ratios measured (below the LP-DOAS detection limit of 0.9 pptv) are not consistent with satellite observations if IO is confined to the MBL. The IOx loading is consistent with the observed absence of strong ozone depletion and nucleation events, indicating a small impact of iodine chemistry on these climatically relevant factors in the eastern Pacific MBL. © 2012. American Geophysical Union. Source

Mahajan A.S.,Laboratory for Atmospheric and Climate Science CIAC | Sorribas M.,National Institute for Aerospace and Technology INTA | Martin J.C.G.,Laboratory for Atmospheric and Climate Science CIAC | MacDonald S.M.,University of Leeds | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2011

Simultaneous measurements of atomic iodine (I), molecular iodine (I 2) and ultrafine particles were made at O Grove, Galicia (42.50° N, 8.87° W), on the northwest coast of Spain. The observations show a strong tidal signature, and indicate that the most probable sources of reactive iodine species are the exposed macroalgae during low tide. For the first time, I 2 and I were concurrently measured revealing a high average I2/I ratio of ∼32, which is higher than previously inferred by modelling studies. A 1-dimensional photochemical model is employed to simulate the observations showing that the high I2/I ratio can be reproduced in the presence of fast vertical mixing close to the surface, or using an extra chemical loss for I atoms with an unknown species. There is a lack of strong correlation between the I2/I and ultrafine particles, indicating that although they both have macroalgal sources, these were not at the same location. The model simulations also suggest that the source of the observed ultrafine particles is likely not very close to the measurement site, in order for the particles to form and grow, but the source for I and I2 must be local. Finally, the effect of NOx levels on iodine oxides, and the conditions under which iodine particle bursts will be suppressed, are explored. © 2011 Author(s). Source

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