COBRA Background information
Source: environment.data.gov.uk (2018-06-19)

COBRA (impact of COmbined iodine and Bromine Release on the Arctic atmosphere): Air-Surface Interactions Properties measurements from Airborne, Ground-based and Laboratory instrumentation. COBRA (impact of COmbined iodine and Bromine Release on the Arctic atmosphere) is a UK IPY (International Polar Year) consortium that aims to investigate the release mechanisms of iodine in the Arctic and the potential combined effects of iodine and bromine on its atmosphere. The team measured reactive inorganic halogens (BrO, IO, OIO, I2), O3, Hg, HOx, HCHO, NOx, VOCs and reactive halocarbons from temporary laboratories located on the eastern shore of Hudson Bay, north of Kuujjuarapik, during February-March 2008. Met balloons and O3 sondes were launched daily. COBRA set up an ice camp and flux chamber experiments ~500 m into the bay to directly measure halogen emissions and ozone deposition, and measured physical, chemical and biological characteristics of the sea-ice (and potentially of frost flowers) at different depths. The project is linked with OOTI, which carried out a simultaneous field experiment at Kuujjuarapik.

COBRA - Background Information
- Introduction (#intro)
- 2.1 - Previous work on polar bromine release and ozone and mercury depletion events (#2.1)
- 2.2 - Potential role of frost flowers and other surfaces for halogen release (#2.2)
- 2.3 - Potential sources and role of iodine in the Arctic (#2.3)
- 2.4 - Potential for future change in Arctic halogen-related processes (#2.4)
- 3.1 - Field site (#3.1)
- 3.2 - Mesurements and techniques (#3.2)
- 3.3 - Deliverables (#3.3)
1 - Introduction

2 - Rationale

2.1 - Previous work on polar bromine release and ozone and mercury depletion events

Every HOBr molecule entering the liquid phase has the potential to release two bromine atoms to the gaseous phase, resulting in an exponential increase of Br, the so-called "Bromine explosion".

The resulting photolysable BrX molecules rapidly produce Br atoms that enter various ozone-destroying cycles:

Cycle I will dominate at high BrO levels, and cycle II at low BrO levels. The re-formation of soluble HOBr(g) in Cycle II, which re-enters the aqueous phase either through uptake on sea-salt aerosol or direct deposition to the snow-pack/sea-ice, results in an autocatalytic mechanism.

Schroeder et al. (1998) (references.html) first observed the rapid decrease in Hg atoms, now referred to as "MDEs" (mercury depletion events) in the Arctic. The MDEs are accompanied by increases in oxidised, but so far unspeciated, mercury in the snowpack, potentially leading to bioaccumulation of soluble and toxic forms of mercury. Recent measurements of the rate coefficients for reactions of a number of halogen gases with Hg suggested that Br atoms could be a major reactant with Hg in the polar atmosphere (Ariya et al., 2002 (references.html)), and subsequent studies have supported this (e.g. Calvert and Lindberg 2004a; Goodsite et al., 2004; Skov et al., 2004 (references.html)). BrO may also be an important reactant, but there are insufficient studies on its rate of reaction with Hg vapour and its concentration in the polar boundary layer. There has been a recent increase in Hg in the Arctic biosphere, and it has been hypothesized that this results primarily from increases in atmospheric oxidant levels and/or reactive bromine rather than from an increase in Hg emissions (OASIS science plan (http://www.chem.purdue.edu/arctic/OASISHomePage.htm)).

It has been suggested that ozone and mercury depletion events apparently operate almost exclusively in polar spring either (a) because only this season has the combination of strong surface inversions (i.e. isolation of boundary layer air from free tropospheric air), sunlight and sea ice (Lehrer et al., 2004 (references.html)), or (b) because the asymmetry of sea ice/frost flower production compared to the amount of sunlight leads to a strong spring maximum in their product (Kaleschke et al., 2005 (references.html)). However, both of the proposed drivers for this seasonality, and the initial source of bromine atoms required to form HOBr and thus initiate the chain destruction of ozone, are controversial.

2.2. - Potential role of frost flowers and other surfaces for halogen release

Brines and frost flowers themselves may be responsible for a significant fraction of sea salt aerosol concentrations over the polar regions (Rankin et al., 2002 (references.html)). However, under typical Arctic conditions, even a flat sea-ice surface (i.e., no frost flowers) provides a factor of ~1000 higher surface area than sea salt aerosol (Lehrer et al., 2004 (references.html)). The latter modelling study of Lehrer et al. (2004) (references.html), although highly parameterised, found that sea salt aerosol alone was not sufficient to sustain the elevated levels of gas phase bromine observed in polar spring, although is an efficient recycler of more stable bromine species such as HBr. However, the study of Evans et al. (2003) (references.html) was able to adequately simulate the chemistry occurring within an ODE through the use of aerosols alone. Thus there are competing hypotheses for the relative role of the surface and aerosol phase in the production and recycling of bromine. The full suite of analytical tools we will deploy during COBRA will allow these hypotheses to be tested more thoroughly than previous studies have allowed.

2.3 - Potential sources and role of iodine in the Arctic

Further evidence of iodine in the polar atmosphere comes from recent observations of reactive organoiodines including di-iodomethane (CH2I2) during spring at Kuujjuarapik on the south-east shore of Hudson Bay, at the highest concentrations ever observed in air and associated with trajectories across the frozen Bay with no observable leads (L. J. Carpenter et al., COBRA PI, submitted to ES&T, 2005 (references.html)). The absence of local ice leads coupled with the extremely short atmospheric lifetime of CH2I2 indicated that production was from the surface of the sea-ice/snowpack over Hudson Bay. We proposed 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/snow pack, and reported laboratory data to support this mechanism. The presence of this mechanism in the natural world (as opposed to in the lab) is at present entirely speculative, however, it might explain the so far puzzling enrichment in CHBr3 observed in upper sea-ice (enhanced in salinity but low in chlorophyll) of the Canadian Arctic (). It also suggests the possibility for photochemical inorganic iodine release from sea-ice, snow-pack and/or FF, analogous to that recently observed by (references.html>)Zingler and Platt (2005) (references.html) over the Dead Sea, and consistent with the Antarctic IO observations of Saiz-Lopez and J. M.C. Plane described above. Photochemical reactions in the snow are known to release a wide range of trace gases to the polar atmosphere (e.g. Sumner and Shepson., 1999 (references.html)). Photochemistry within sea-ice is also perfectly feasible, with ice potentially more transparent to the UV than to visible radiation (Belzile et al., 2000 (references.html)), yet has not been well studied. In sea-ice, fresh-water ice co-exists with solid salts, concentrated brines, gases and marine-derived organic material, thus starting material is present for both organic and inorganic halogen release.

These recent and so far unpublished IO and organoiodine observations of the COBRA team, in separate polar locations, suggest a widespread and likely abiotic/photochemical source of iodine to the polar atmosphere. The impact of such emissions may be significant. Theoretical studies indicate that iodine compounds added to a Br2/BrCl mixture in the Arctic atmosphere have a significantly greater ozone and mercury depletion effect than additional bromine molecules (Calvert and Lindberg, 2004a and 2004b (references.html)). The role, if any, of iodine compounds on Hg-atoms is unknown. Direct reactions of I atoms with Hg may be unimportant (Goodsite et al., 2004 (references.html)), however a recent study by Calvert and Lindberg (2004b) (references.html) points out a potential indirect effect of iodine through an enhancement in [Br] mediated by IO and BrO interactions. In mid-latitude coastal locations, release of iodine is known to result in new particle formation and there is a possibility that similar mechanisms operate in the Arctic.

2.4 - Potential for future change in Arctic halogen-related processes

3 - Field Site, Measurements and techniques, and Deliverables

3.1 - Field site

The measurement campaign took place during February 2008 and March 2008, at Kuujjuarapik, on the south east coast of Hudson Bay in Quebec, Canada. The project was based at the Centre d'Etudes Nordique Whapmagoostui-Kuujjuarapik research station operated by Laval University, Montreal with measurements being made at the research station, and a temporary site on the coast a few kilometres away. The coastal site consisted of two container labs on the shore with additional measurements being made approximately 300m out on the sea ice. The Whapmagoostui-Kuujjuarapik research station is equipped with research laboratories, a weather station, and accommodation blocks, and also has existing long term O3 and Hg measurements.

3.2 - Measurements and techniques

Details of measurements and techniques are given in the table below.

Kuuj = Kuujaparik campaign, Flux = flux measurements from lead, Lab = laboratory measurements of frost flower surrogates.

3.3 - Deliverables

The specific project deliverables are:
- Field/lab-testing and validation of newly-developed instruments including CE-DOAS, BBCEAS and denuder tube-ICP/MS for measurements of reactive halogen species
- Extremely comprehensive atmospheric data set of trace gases, particularly reactive halogen species, and aerosol physical and chemical characteristics in the sub Arctic atmosphere.
- Significantly improved understanding of the role of frost flowers and other potential sources (sea-ice, snow-pack, sea salt aerosol, diatoms) in halogen release.
- Development of techniques to create frost flowers in the field.
- New information regarding the spatial and temporal variability of O3, Hg, BrO, IO, particles and other important polar tropospheric constituents.
- For the first time, an observationally-based assessment of whether iodine leads to new particle formation in the Arctic troposphere.
- Improved knowledge of the depletion and transformations of mercury in the Arctic, including the role, if any, of iodine.
- An assessment of the role of halogens in the local ozone budget of the Arctic boundary layer and in the global free troposphere.
- Contribution to current knowledge of how anthropogenic changes have impacted the photochemistry of halogen chemistry in the Arctic.
- Exploration of possible climate change effects on Arctic halogen related chemistry.
COBRA will strengthen the science of polar sea-ice/atmosphere exchange, and allow many UK atmospheric chemistry researchers so far not active in this field, but with highly relevant expertise, to establish themselves in polar research and to develop links with international researchers in the field.