Collaborative Research: A Synthesis of Existing and New Observations of Air-Snowpack Exchanges to Assess the Arctic

积雪内部、上方和下方发生的化学和生物过程影响对流层臭氧。迄今可获得的测量数据和简化的模式研究表明，由此产生的对流层O3的影响是显著的，但现有的测量数据和目前的模式能力不足以对其大小进行定量估计。由于气候变化导致的积雪、海冰和永久冻土范围的持续变化和预期的未来变化，这将改变未来积雪O3的影响，因此提高我们对积雪-大气O3交换的理解尤为重要。该项目提供了一种解决这一需求的综合方法，利用实地测量来填补当前知识中的关键空白，并将新的和现有的数据综合到化学-气候模型中。O3和NOx （NO+NO2）的空气-雪交换通量将在不同雪/土地类型的多个站点进行测量，每个站点都将进行较长时间的测量，以捕捉日晒变化、积雪特性和（如适用）土壤温度和土壤NOx排放的影响。测量将包括积雪内部和上方的O3和NOx水平和梯度以及积雪上方两个高度的涡旋相关O3通量；辅助测量将描述大气湍流、光化通量、微气象参数以及积雪的物理和辐射特性。实地地点包括Summit，格陵兰（代表冰川积雪），Toolik Lake，阿拉斯加（代表永久冻土和冰冻湖泊上的积雪）和密歇根理工大学运营的Aspen FACE研究站点（代表生物活性土壤上的积雪）。在科罗拉多州桌山进行仪器调试的额外测量将提供间歇性积雪的信息。积雪过程的新参数化将被开发并纳入全球化学-气候模式ECHAM4和echam5 -凌乱的单柱模式（SCM）版本。这些参数化将被设计用来描述潜在的过程，并捕捉现有的和新的实地测量之间的变化，这些变化将用于模型评估。新的模式系统将用于模拟空气-雪O3和NOx交换对北极对流层O3收支的影响。这项工作将填补对积雪过程影响O3的现有认识空白，包括积雪对O3的吸收和积雪下生物活动的作用，积雪中NOx的释放，以及积雪排放O3前体导致的边界层O3的产生。它将首次测量永久冻土层和冰冻湖泊上积雪的积雪-空气O3和NOx通量，并对非永久冻土层上的积雪进行最彻底的测量。新的积雪交换模型将是目前化学气候模型中积雪影响模拟的一个非常重要的进步，并将使这些模型能够更好地描述变化的北极气候和环境系统之间的联系。它的使用将首次评估积雪光化学过程对北极和亚北极对流层O3收支的影响，并将为评估气候变化将通过改变积雪和永久冻土范围对对流层O3收支施加的预期影响提供基础。

Chemical and biological processes occuring within, above, and below snowpacks influence tropospheric ozone. Measurements available to date and simplified modeling studies indicate that the resulting impact on tropospheric O3 is significant, but available measurements and current modeling capabilities are insufficient for a quantitative estimate of its magnitude. It is of particular importance to improve our understanding of snowpack-atmosphere O3 exchanges because of ongoing and expected future alterations in snow, sea-ice and permafrost extent resulting from climate change, which will alter snowpack O3 impacts in the future. This project provides an integrated approach to address this need, using field measurements to fill key gaps in current knowledge and synthesizing the new and existing data into a chemistry-climate model.Air-snow exchange fluxes of O3 and NOx (NO+NO2) will be measured at multiple sites with different snow/land types, each for an extended period to capture effects of changing insolation, snowpack properties and (where applicable) soil temperature and soil NOx emissions. Measurements will include O3 and NOx levels and gradients both within and above the snowpack and eddy-correlation O3 fluxes at two heights above the snowpack; ancillary measurements will characterize atmospheric turbulence, actinic flux, micrometeorological parameters and the snowpack's physical and radiative properties. Field locations include Summit, Greenland (representing glacial snowpack), Toolik Lake, Alaska (representing snowpack above permafrost soil and snowpack over frozen lakes) and the Aspen FACE research site operated by Michigan Tech (representing snowpack above biologically active soil). Additional measurements for instrument shakedown at Table Mountain, Colorado, will provide information on intermittent snowpack.New parameterizations of snowpack processes will be developed and incorporated into single column model (SCM) versions of the global chemistry-climate models ECHAM4 and ECHAM5-MESSy. These parameterizations will be designed to describe the underlying processes and to capture variations among the available and new field measurements, which will be used for model evaluation. The new model system will be used to simulate the impact of air-snow O3 and NOx exchange upon the arctic tropospheric O3 budget.This work will close existing gaps in understanding of snowpack processes affecting O3, including O3 uptake to snow and the role of biological activity below snowpacks, NOx release from snow, and boundary layer O3 production resulting from snowpack emissions of O3 precursors. It will provide the first measurements of snow-air O3 and NOx fluxes for snow over permafrost and snow over frozen lakes, and the most thorough measurements available for snow over non-permafrost soil. The new snowpack-exchange model will be a very significant advancement over current simulations of snowpack impacts in chemistry-climate models, and will allow such models to better describe the connections between changing Arctic climate and environmental systems. Its use will produce the first assessment of the impact of snowpack photochemical processes upon the arctic and subarctic tropospheric O3 budget, and will provide the basis for assessing the expected impact that climate change will exert upon the tropospheric O3 budget through changing snowcover and permafrost extent.