Title: Possible Evidence for a Connection between Methyl Iodide Emissions and Saharan Dust
Citation: JOURNAL OF GEOPHYSICAL RESEARCH vol. 112 p. D07302-1 D07302-11
Publication Year: 2007
JRC N°: JRC36514
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC36514
Type: Articles in periodicals and books
Abstract: Methyl iodide has been measured during two field campaigns in the Atlantic region in 2002. The first took place in July-August at 2300 m on the island of Tenerife, while the second was a shipborne, East-West crossing of the Tropical Atlantic at 10°N in October-November of the same year. Both campaigns were periodically impacted by dust, advected from Africa in trade winds. Unexpectedly, during these dust events, methyl iodide mixing ratios were observed to be high relative to other times. Backward calculations with the particle dispersion model FLEXPART show the origin of the dust storms as Mauritania and southern Algeria for the ground and ship based campaigns, respectively. The dust laden air travelled from its source above the marine boundary layer to the measurement region. Based on the field data correlations and the simulations, we suggest that dust stimulated emission of methyl iodide has occurred. To test this hypothesis, dust samples were collected from the identified source regions and added to filtered Atlantic seawater. This rapidly produced methyl iodide. Further tests established that the addition of iodide increased the yield and iodide with H2O2 was greater still. This was found for both sterilised and non-sterilised samples. We conclude that there is an abiotic methyl iodide production mechanism that can occur via substitution, analogous to those in soil, rather than radical recombination. This may occur when dust contacts seawater or when marine water vapour condenses on dust. This hypothesis appears to be consistent with recent long term methyl iodide datasets from Tasmania and may help resolve current uncertainties in the iodine cycle.
JRC Directorate:Sustainable Resources

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