In situ measurements of molecular iodine in the marine boundary layer: the link to macroalgae and the implications for O<sub>3</sub>, IO, OIO and NO<sub>x</sub>
2010
R.-J. Huang | K. Seitz | J. Buxmann | D. Poehler | K. E. Hornsby | L. J. Carpenter | U. Platt | T. Hoffmann
"Single-point" in situ measurements of molecular iodine (I<sub>2</sub>) were carried out in the coastal marine boundary layer (MBL) using diffusion denuders in combination with a gas chromatography-mass spectrometry (GC-MS) method. Comparison measurements were taken at Mace Head and Mweenish Bay, on the West Coast of Ireland. The observed mixing ratios of I<sub>2</sub> at Mweenish Bay are much higher than that at Mace Head, indicating the emissions of I<sub>2</sub> are correlated with the local algal biomass density and algae species. The concentration levels of I<sub>2</sub> were found to correlate inversely with tidal height and correlate positively with the concentration levels of O<sub>3</sub> in the surrounding air. However, the released I<sub>2</sub> can also lead to O<sub>3</sub> destruction via the reaction of O<sub>3</sub> with iodine atoms that are formed by the photolysis of I<sub>2</sub> during the day and via the reaction of I<sub>2</sub> with NO<sub>x</sub> at night. IO and OIO were measured by long-path differential optical absorption spectroscopy (LP-DOAS). The results show that the concentrations of both daytime and nighttime IO are correlated with the mixing ratios of I<sub>2</sub>. OIO was observed not only during the day but also, for the first time at both Mace Head and Mweenish Bay, at night. In addition, I<sub>2</sub> was measured simultaneously by the LP-DOAS technique and compared with the "single-point" in situ measurement. The results suggest that the local algae sources dominate the inorganic iodine chemistry at Mace Head and Mweenish Bay.
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