Abstract
Abstract. Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive data set of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol−1 (30% uncertainty) and, complemented with additional field campaigns, this data set confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75 % to the IO budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.
Highlights
The atmospheric relevance of reactive halogens became clear decades ago when their potential to catalytically destroy ozone (O3) was first recognised in the polar stratosphere (Molina and Rowland, 1974) and later on in the troposphere (e.g. Barrie et al, 1988)
We investigate the contribution of the OSG and ISG fluxes to the iodine oxide (IO) budget in the marine boundary layer (MBL)
We present a comprehensive set of observations of IO mixing ratios in the marine boundary layer obtained after the Malaspina 2010 circumnavigation, covering three non-polar oceans and both hemispheres
Summary
The atmospheric relevance of reactive halogens became clear decades ago when their potential to catalytically destroy ozone (O3) was first recognised in the polar stratosphere (Molina and Rowland, 1974) and later on in the troposphere (e.g. Barrie et al, 1988). Since the first study to deal with the tropospheric relevance of inorganic iodine (Chameides and Davis, 1980), major efforts have been made to detect reactive iodine species in their main source region: the oceans (Saiz-Lopez et al, 2012 and references therein). In several one-dimensional model studies, simulated emissions of molecular iodine (I2) were used to fit IO observations (e.g. Mahajan et al, 2010; Großmann et al, 2013); the recent work of Lawler et al (2014) with the first observation of I2 in the remote MBL confirmed that the emission of I2 is still insufficient to explain the observed levels of IO. By means of a global model including OSG and ISG oceanic emissions, we investigate the geographical emission patterns of both iodine precursors and their contribution to the IO budget in the marine environment.
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