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

大气气溶胶颗粒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与颗粒尺寸分布和组成的现场观测显示出相当大的差异，部分原因是颗粒动力学的复杂性，包括干沉积。鉴于森林覆盖面广阔，森林上的颗粒沉积速度相对较高，森林生态系统在消除气溶胶颗粒方面的作用正引起一些科学学科和监管机构越来越多的关注。然而，仍然存在重大不确定性，原因是：(1)与实地测量颗粒大小、溶解通量和平均浓度有关的困难，(2)缺乏对冠层介质以及更重要的树叶表面特征的详细和同时测量，(3)在描述冠层内部和紧靠冠层上方的输送剂(湍流)的所有主要特征方面存在困难。本项目将通过探索：(1)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，在多个层次尺度(树叶到树冠)上使用综合实验和建模方法来解决在森林表面上颗粒沉积的三个关键方面，以及(3)从方面[1]和[2]到整个生态系统的放大结果。冠层尺度尺寸分辨的颗粒通量和平均浓度分布将在具有“理想”微气象条件的不同林地(针叶和阔叶)中进行测量，并在环境室内进行对照实验。这些实验的发现将通过考虑叶片表面的属性、涡轮和潜热成分来指导在叶片水平上开发新的颗粒收集方案。此外，还将探索如何将这些结果从现在可以从遥感平台获得的测量结果(例如，叶面积密度)提升到冠层水平，这些测量结果可以使用多层和粒子尺寸分辨的冠层湍流闭合模型。模式结果将在三个森林地点使用位于树冠上方和林下的尺寸分辨平均颗粒浓度分布和两级涡旋-协方差颗粒通量系统进行评估。本项目将在过程水平上改进对颗粒干沉积的理解，并提供适用于从地球系统模型到区域尺度空气质量模式的一系列数值模式的机械描述。为了最大限度地利用所得出的研究成果，将通过一个项目网站向公众公布这些数据集和模型。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-大气能量交换、气溶胶、碳、水、有机物和氮)研究小组和欧洲合作者的互动，与更广泛的科学界接触。环境科学学士(http://www.indiana.edu/~bses/))课程将为本科生提供机会，让他们获得顶尖的研究经验。

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.