Sources of Organic and Inorganic Halogens to the Polar and Temperate Marine Boundary Layer

Very short lived halogenated substances (VSLH) are of importance for the transport of reactive halogens to the troposphere and lower stratosphere, whereas molecular halogens are of specific importance to the Marine Boundary Layer (MBL). This thesis describes the field deployment of a ground based gas chromatography mass spectrometry (GC/MS) in the Canadian sub-Arctic for the determination of VSLH in seawater/sea-ice and air with a view to identify dominant sources to the MBL in the region. MBL mixing ratios of VSLH were determined from a surface site (55.28°N, 77.77°W) on the south east of Hudson Bay,(Kuujjuarapik, Canada) during the 19th -27th of February. Elevated mixing ratios of the Volatile Organic Iodine Compounds (VOIC) coincided with airmasses reaching the ground site that had previously transected regions of open water in the Bay (between 10 – 200 km away), suggesting leads/polynyas are the dominant source of VOIC within the region.

This observation is supported by laboratory experiments conducted with artificial sea ice in a cold chamber (School of Earth and Environment, Leeds University) in which physico-chemical properties of the hypersaline brine, sea-ice and the underlying seawater were measured to quantify the vertical transport of a comprehensive range of volatile organic iodinated compounds (VOICs) at air temperatures of -3 and -14 oC. The results suggest that VOIC gas transfer velocities from diffusion through the sea-ice alone are at least 60 times lower at -3 ºC than gas exchange from leads and polynas during the winter (assuming a sea-ice fractional coverage of 0.1). This has significant implications for in situ VOIC losses within the brine from chlorination, hydrolysis and photolysis processes and it is unlikely that measurable concentrations of VOICs would survive vertical transport from the underlying seawater to the surface sea ice quasi-liquid layer.

Further laboratory work within this thesis suggests that gaseous I2 evolution from the oxidation of iodide in the world’s oceans by atmospheric ozone is a viable source of iodine to the MBL, but its strongly constrained by the iodide and dissolved organic carbon (DOC) content of the surface ocean.