Measurements and modelling of molecular iodine emissions, transport and photodestruction in the coastal region around Roscoff
1Department of Physics and Astronomy, University of Leicester, Leicester, UK.
2Department of Chemistry, University of Leicester, Leicester, UK
3Department of Chemistry, University of Cambridge, Cambridge, UK
4School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
5Station Biologique de Roscoff, UPMC-CNRS, UMR7139, France
6School of Chemistry, University of Leeds, Leeds, UK
Abstract. Emissions from the dominant six macroalgal species in the coastal regions around Rosccoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLE) campaign undertaken in September 2006. A 2-D model was used to explore the relationship between point and line measurements of molecular iodine concentrations, and total regional emissions, based on seaweed I2 emission rates measured in the laboratory. The relatively simple modelling technique has produced modelled point and line data, which compare quantitatively with campaign measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLE. During nightime, absolute concentrations in the region of 5 pptv are predicted and measured in the LP-DOAS measurements, with site concentrations predicted and measured up to 40 pptv, compatible with concentrations above Laminariales beds of approximately 2.5 ppbv. Daytime measured concentrations of I2 at site correlate with modelled production and transport processes, however complete recycling of photodissociated I2 is required in the model to quantitatively match measured concentrations. Additional local source terms are suggested to provide a feasible mechanism to account for this discrepancy.Total of I2 emissions over the 100 km2 region around Roscoff are calculated as 1.5×1019 molecules per second during the lowest tides.