Photochemical oxidation in snow and sea-ice by organic matter photocatalysis in the visible: An international field and modelling study.

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ABSTRACT The PI proposes to undertake, as part of an international polar campaign, a fieldtrip to Barrow (Alaska) in the Arctic where he will characterize the visible optical properties of snowpack and sea-ice and use the results to create a radiative-transfer photochemical model of the snow and sea ice that will allow (I) fluxes of reactive nitrogen species to the atmosphere to be estimated. (II) test a newly proposed chemical mechanism that may be responsible for driving chemical oxidation in snowpack and (III) calculate photosynthetic active radiation in snowpack. SUMMARY Sunlit snowpacks and sea-ice produce a flux of chemicals from the snow or ice to the atmosphere. With up to 50% of land in the Northern hemisphere (North of 20N) being covered with seasonal snow this presents a large flux of chemicals to the atmosphere. This chemical flux has two consequences (1) it makes the atmosphere more oxidising and (2) it changes the concentration of chemicals in snow and ice cores. Chemical records in ice cores drilled in Polar Regions are used to understand previous climate change, and thus predict future climate change. The photochemical processes that occur in sunlit sea ice are similar to those that occur in snowpack. Sunlight also drives the primary production of the plants and algae in the sea ice, and provides a nutrient flux to the ocean on ice break-up. The aim of this project is to test whether an exciting new photochemical mechanism proposed from laboratory experiments and published in Nature ((2006) 440(9),195) and Faraday discussions ((2005), 130,195) is possible in snow and ice: Can nitrous acid and hydrogen peroxide can be produced in and on snow and sea ice by a sunlight driven chemical reaction involving natural organic matter in snow and ice? The chemical mechanism is catalytic and does not consume the organic matter. A US-French-Italian-British Arctic field trip (Barrow) will quantify the fluxes of chemicals (NO, NO2, HONO and HNO3) from the snowpack using measurement of chemical fluxes, momentum fluxes, chemical and physical properties of the snow, and the measurement of the sunlight on and in the snowpack. The PI will provide the measurements of the sunlight irradiance in the snow and above the snow and modelling the flux of chemicals from the snow to compare with the field measurements and thus test the chemical mechanism. The PI is one of only two groups worldwide that can undertake this work. Barrow is a cost effective, well-resourced location, in which to study sea-ice and snow. The PI is not reliant on the international partners (and their funding councils) to fulfil ALL of the objectives, in this proposal. The PI will measure the albedo and light transmission of many snows and sea ice with a small, portable, battery powered item of equipment that can be transported in backpacks. and snow machines. The PI will also measure the sunlight irradiance from the sun and snow reflectivity. A model will be used to compute the amount of chemistry driven by this sunlight in and above the snow. The model will be used to predict fluxes of HONO (and NO, NO2) from the snow and compare to concurrent a measurements of these gases at Barrow as part of the large US led field campaign. The PI's estimates of the flux of HONO from the snowpack owing to this mechanism span a factor of 1000, this project could reduce that to a factor of ~2 The International Polar Year makes this work very timely. Equipment and techniques of this project have been tested in previous polar field campaigns (including Antarctica) and are achievable; this project is low risk and high reward (four papers, a visible RT model, and an assessment of the potential chemical mechanism) for a small amount of money. The fieldwork will last 21 days. The following months will be spent developing a radiative transfer model of the snow and sea-ice to estimate these fluxes with simple mathematical function for other users.