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会影响对流层臭氧。迄今可用的测量和简化的模拟研究表明，由此产生的对对流层臭氧的影响是显著的，但现有的测量和现有的模拟能力不足以定量估计其大小。提高我们对积雪-大气臭氧交换的理解尤为重要，因为气候变化导致的雪、海冰和永冻土范围正在发生和预期的变化，这将改变未来积雪对大气臭氧的影响。该项目提供了一种综合方法来满足这一需求，使用现场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合成到化学气候模型中。将在多个不同雪/土地类型的地点测量臭氧和NOx(NO NO2)的气-雪交换通量，每个站点都在较长的一段时间内捕捉变化的日照、积雪性质以及(如果适用)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臭氧和氮氧化物水平和梯度以及积雪上方两个高度的涡旋相关臭氧通量；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。现场地点包括格陵兰的Summit(代表冰川积雪)、阿拉斯加的Toolik湖(代表永久冻土上方的积雪和冰冻湖泊上方的积雪)，以及由密歇根理工学院运营的Aspen Face研究站点(代表生物活性土壤上方的积雪)。科罗拉多州桌山仪器安放的额外测量将提供有关间歇性积雪的信息。积雪过程的新参数将被开发并纳入全球化学-气候模式ECHAM4和ECHAM5-MISY的单柱模式(SCM)版本。这些参数将被设计来描述基本过程，并捕捉现有和新的实地测量之间的差异，这些差异将用于模型评估。新的模式系统将被用来模拟大气-雪层臭氧和NOx交换对北极对流层臭氧预算的影响。这项工作将填补影响臭氧的积雪过程的现有理解空白，包括臭氧对雪的吸收和积雪下生物活动的作用，雪中NOx的释放，以及臭氧前体积雪排放的边界层臭氧的产生。它将首次测量永久冻土上的雪和冻结的湖泊上的雪-空气臭氧和氮氧化物的通量，并提供可用于非永久冻土上的雪的最彻底的测量。与目前化学气候模型中积雪影响的模拟相比，新的积雪交换模型将是一个非常重大的进步，并将使此类模型能够更好地描述不断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臭氧预算的影响，并将为评估气候变化通过改变积雪和永久冻土范围对对流层臭氧预算产生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.