Collaborative Research: Up-scaling from Leaf to Canopy the Aerosol-sized Particle Collection Mechanism Within a Non-uniform Canopy Medium

大气气溶胶粒子浓度是理解历史和未来可能的气候强迫的最大不确定性之一，甚至区域大气化学模型也显示出与现场观测的粒子大小分布和组成相当大的差异，部分原因是粒子动力学的复杂性，包括干沉降。由于森林覆盖面积大，森林上空的颗粒沉积速度相对较高，森林生态系统在清除气溶胶颗粒方面的作用正引起一些科学学科和管理机构的日益关注。然而，由于以下原因，仍然存在重大的不确定性：（1）与颗粒大小分辨通量和平均浓度的实地测量相关的困难，（2）缺乏对冠层介质的详细和同步测量，更重要的是，树叶表面特征，以及（3）在描述冠层内和冠层上方的运输介质（湍流）的所有主要特征方面存在挑战。这个项目将解决三个关键方面的颗粒沉积到森林表面使用相结合的实验和建模方法在多层次尺度（叶到冠层）通过探索：（1）在叶尺度上的叶收集机制的相对重要性和正确描述，（2）叶和非叶元素之间的沉积通量分配，以及（3）将方面[1]和[2]的结果放大到整个生态系统。将在具有“理想化”微气象条件的各种森林地点（针叶树和阔叶树）和在环境室中的受控实验中测量冠层尺度尺寸分辨的颗粒通量和平均浓度分布。从这些实验的结果将指导新的颗粒收集计划的发展，在叶片水平占叶表面特性，涡轮和热泳组件。此外，将探讨如何将这些结果放大到冠层水平，从现在可以从遥感平台（如叶面积密度）获得的测量结果，使用多级和颗粒大小分辨冠层湍流闭合模型。模型结果将在三个森林站点进行评估，使用尺寸分辨的平均粒子浓度分布图和位于树冠上方和林下的两级涡动协方差粒子通量系统，该项目将提高对粒子干沉积过程的理解，并提供适用于从地球系统模型到区域尺度空气质量模型的一系列数值模型的机制描述。为了便于最大限度地利用所得出的研究产品，将通过一个项目网站提供数据集和模型的电子版。该项目将支持一名博士后学者和一名研究生，他们将有机会通过与BEACHON（生物圈-大气能量，气溶胶，碳，H2O，有机氮交换）研究团队和欧洲合作者的互动与更广泛的科学界接触。本科生的机会将在BSES（科学在环境科学学士，http：//www.indiana.edu/cubbses/）计划进行他们的顶点研究经验提供。

Atmospheric aerosol particle concentrations represent one the largest uncertainties in understanding of both historical and possible future climate forcing, and even regional atmospheric chemistry models exhibit considerable discrepancies with in situ observations of particle size distribution and composition in part because of the complexities of particle dynamics, including dry deposition. Given the expansive forest cover and relatively high particle deposition velocities over forests, the role of forested ecosystems in removing aerosol particles is drawing increased attention in a number of scientific disciplines and regulatory agencies. However, significant uncertainties remain due to: (1) difficulties associated with field measurements of particle size resolved fluxes and mean concentrations, (2) lack of detailed and simultaneous measurements of the canopy medium and, more importantly, foliage surface characteristics, and (3) challenges in describing all the main features of the transporting agent (turbulence) within and immediately above the canopy. This project will address three key aspects of particle deposition onto forested surfaces using a combined experimental and modeling approach at multiple hierarchical scales (leaf-to-canopy) by exploring: (1) the relative importance of, and correct descriptions of, the foliage collection mechanisms at the leaf scale, (2) deposition flux partitioning between foliar and non-foliar elements, and (3) up-scaling results from aspects [1] and [2] to the entire ecosystem.Canopy scale size-resolved particle fluxes and mean concentration profiles will be measured in a diverse array of forested sites (conifers and broadleaf) endowed with "idealized" micrometeorological conditions and in controlled experiments in an environmental chamber. Findings from these experiments will guide the development of new particle collection schemes at the leaf level by accounting for leaf surface properties, turbo- and thermophoretic components. Also, how to upscale these results to the canopy level from measurements that can now be acquired from remote sensing platforms (e.g. leaf area density) using multi-level and particle size-resolved canopy turbulence closure models will be explored. The model results will be evaluated at three forested sites using size-resolved mean particle concentration profiles and two-level eddy-covariance particle flux systems positioned above the canopy and in the understory.This project will provide improvements in process-level understanding of particle dry deposition and for mechanistic descriptions suitable for application in a range of numerical models from earth system models to regional scale air quality models. To facilitate maximal use of the research products derived, the data sets and the models will be made publically accessible via a project website. The project will support one post-doctoral scholar and one graduate student, who will have opportunity to engage with the broader scientific community via interaction with the BEACHON (Biosphere-atmosphere Exchange of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen) research team and European collaborators. Opportunities for undergraduate students will be offered within the BSES (Bachelor of Science in Environmental Science, http://www.indiana.edu/~bses/) program to undertake their capstone research experiences.