Abiotic source of reactive organic halogens in the sub-arctic atmosphere?
ABSTRACT Recent theoretical studies indicate that reactive organic iodocarbons such as CH2I2 would be extremely effective agents for tropospheric Arctic ozone depletion and that iodine compounds added to a Br2/BrCl mixture have a significantly greater ozone (and mercury) depletion effect than additional Br2 and BrCl molecules. Here we report the first observations of CH2I2, CH2IBr, and CH2ICl in Arctic air, as well as other reactive halocarbons including CHBr3, during spring at Kuujjuarapik, Hudson Bay. The organoiodine compounds were present atthe highest levels yet reported in air. The occurrence of the halocarbons was associated with northwesterly winds from the frozen bay, and, in the case of CHBr3, was anticorrelated with ozone and total gaseous mercury (TGM), suggesting a link between inorganic and organic halogens. The absence of local leads coupled with the extremely short atmospheric lifetime of CH2I2 indicates that production occurred in the surface of the sea-ice/overlying snowpack over the bay. We propose an abiotic mechanism for the production of polyhalogenated iodo- and bromocarbons, via reaction of HOI and/or HOBr with organic material on the quasi-liquid layer above sea-ice/snowpack, and report laboratory data to support this mechanism. CH2I2, CH2IBr, and other organic iodine compounds may therefore be a ubiquitous component of air above sea ice where they will increase the efficiency of bromine-initiated ozone and mercury depletion.
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ABSTRACT:  Volatile halogenated compounds (CHBr3, CH2Br2, CHBr2Cl, and CH2ClI) were measured in the water column and in sea ice brine across the Arctic Ocean, from Barrow, Alaska, to Svalbard, during the Beringia 2005 expedition (August–September) with RV/IB Oden. High concentrations of brominated compounds (up to 42 pmol kg−1 of bromoform) were found under multiyear ice in the surface waters over the Makarov Basin and the Lomonosov Ridge, near the North Pole. Even higher concentrations (bromoform up to 160 pmol kg−1) were found in sea ice brine. We propose that the high load of riverine dissolved organic matter that is transported in the Transpolar Drift is a main factor responsible for the high concentration of brominated volatile compounds found in sea ice brine and upper waters and that cycles of freezing and thawing during the transport enhance the transfer of halocarbons to the seawater. The iodinated compound (CH2ClI) showed a completely different distribution with highest concentrations in water of Pacific origin in the mixed layer and upper halocline of the northern Canada Basin and over the Alpha Ridge. In the southern Canada Basin, low concentrations of halocarbons were found in upper waters. Higher concentrations in water of Pacific origin, especially on the continental shelf, indicate production in the shelf regions, likely in the Chukchi Sea and the East Siberian Sea.Global Biogeochemical Cycles. 12/2013;
Article: Energy and ozone fluxes over sea ice[Show abstract] [Hide abstract]
ABSTRACT: We present surface layer measurements made over Hudson Bay sea ice during February/March 2008 from the COBRA (Impact of combined iodine and bromine release on the Arctic atmosphere) experiment which formed part of the International OASIS (Ocean-Atmosphere-Sea Ice-Snowpack) IPY programme. All components of the local surface energy balance were measured and it was defined by net radiative cooling throughout most of the day, mainly balanced by the conductive heat flux from the warmer sea water to the cooler sea ice at the surface, and a small net radiative warming for a few hours after midday. Unique ground-level ozone fluxes were measured by eddy covariance and deposition velocities ranged from +0.5 mm s−1 (deposition) to −1.5 mm s−1 (emission). Ozone profile measurements suggested ozone flux divergence within the surface layer. The observed bi-directional fluxes and flux divergence with height reveal the complexity of surface ozone fluxes in the Arctic spring time surface layer, and show that ozone exchange with the sea ice surface is best probed using the eddy covariance method alongside frequent or continuous profile measurements. In this study, the local in-situ ozone-halogen photochemistry was identified as weakly controlling the measured ozone flux, whereas horizontal advection and vertical mixing were considered more important in influencing fluxes. Under these conditions, several measurement sites would be desirable in order to quantify the contribution of advection to the local surface exchange.Atmospheric Environment 02/2012; 47:218–225. · 3.11 Impact Factor
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ABSTRACT: Iodine compounds were measured above, below and within the sea ice of the Weddell Sea during a cruise in 2009, to make progress in elucidating the mechanism of local enhancement and volatilisation of iodine. I2 mixing ratios of up to 12.4 pptv were measured 10 m above the sea ice, and up to 31 pptv was observed above surface snow on the nearby Brunt Ice Shelf - large amounts. Atmospheric IO of up to 7 pptv was measured from the ship, and the average sum of HOI and ICl was 1.9 pptv. These measurements confirm the Weddell Sea as an iodine hotspot. Average atmospheric concentrations of CH3I, C2H5I, CH2ICl, 2-C3H7I, CH2IBr and 1-C3H7I were each 0.2 pptv or less. On the Brunt Ice Shelf, enhanced concentrations of CH3I and C2H5I (up to 0.5 and 1 pptv respectively) were observed in firn air, with a diurnal profile that suggests the snow may be a source. In the sea ice brine, iodocarbons concentrations were over 10 times those of the sea water below. The sum of iodide + iodate was depleted in sea ice samples, suggesting some missing iodine chemistry. Flux calculations suggest I2 dominates the iodine atom flux to the atmosphere, but models cannot reconcile the observations and suggest either a missing iodine source or other deficiencies in our understanding of iodine chemistry. The observation of new particle formation, consistent with the model predictions, strongly suggests an iodine source. This combined study of iodine compounds is the first of its kind in this unique region of sea ice rich in biology and rich in iodine chemistry.ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2012; 12(22):11229-11244. · 5.51 Impact Factor