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

摘要作为国际极地活动的一部分，PI建议到北极的巴罗（阿拉斯加）进行实地考察，在那里他将描述积雪和海冰的可见光特性，并使用结果创建雪和海冰的辐射转移光化学模型，该模型将允许（I）估计活性氮物质到大气中的通量。(II)测试一个新提出的化学机制，可能是负责驱动化学氧化在积雪和（III）计算光合有效辐射在积雪。阳光照射下的积雪和海冰产生了一种化学物质从雪或冰到大气中的通量。在北方（北纬20度以北），多达50%的土地被季节性积雪覆盖，这给大气带来了大量的化学物质。这种化学通量有两个后果：（1）它使大气更具氧化性;（2）它改变了雪和冰芯中化学物质的浓度。在极地地区钻取的冰芯中的化学记录被用来了解以前的气候变化，从而预测未来的气候变化。在阳光照射下的海冰中发生的光化学过程与积雪中发生的类似。阳光还驱动着海冰中植物和藻类的初级生产，并在冰破裂时为海洋提供营养流。该项目的目的是测试一种由实验室实验提出并发表在《自然》（Nature）（2006）440（9），195）和《法拉第讨论》（Faraday discussions）（（2005），130，195）中的令人兴奋的新光化学机制在冰雪中是否可能：亚硝酸和过氧化氢可以通过阳光驱动的化学反应在雪和海冰中产生吗？要冰吗化学机理是催化的，不消耗有机物。美国-法国-意大利-英国北极实地考察（巴罗）将通过测量化学通量、动量通量、雪的化学和物理特性以及测量积雪上和积雪中的阳光来量化积雪中化学物质（NO、NO2、HONO和HNO 3）的通量。PI将提供雪中和雪上方阳光辐照度的测量结果，并对雪中化学物质的通量进行建模，以与现场测量结果进行比较，从而测试化学机制。PI是世界上仅有的两个能够承担这项工作的组织之一。巴罗是一个具有成本效益，资源充足的位置，在那里研究海冰和雪。PI不依赖国际合作伙伴（及其资助委员会）来实现本提案中的所有目标。PI将测量许多雪和海冰的反射率和光透射率，使用一种小型便携式电池供电设备，可以放在背包中运输。造雪机PI还将测量来自太阳的阳光辐照度和雪的反射率。一个模型将被用来计算雪中和雪上方的阳光所驱动的化学物质的数量。该模型将用于预测HONO（和NO，NO2）从雪中的通量，并比较这些气体在巴罗作为美国领导的大型现场活动的一部分，同时测量。由于这种机制，PI对积雪中HONO通量的估计跨越了1000倍，本项目可以将其减少到2倍。国际极地年使这项工作非常及时。该项目的设备和技术已经在以前的极地考察（包括南极）中进行了测试，并且是可以实现的;该项目是低风险和高回报的（四篇论文，一个可见的RT模型，以及对潜在化学机制的评估）。实地考察将持续21天。在接下来的几个月里，我们将开发一个雪和海冰的辐射传输模型，以便用简单的数学函数来估计这些通量，供其他用户使用。

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.