Collaborative Research: Understanding Emission Sources and Sinks of Nitrous Acid in North American Forests

该项目侧重于陆地-大气相互作用，以及土壤排放的亚硝酸（HONO）和其他氮氧化物影响大气氧化能力的机制。实验计划包括在受控条件下使用生长室，结合实地数据，研究在北美主要森林地区占主导地位的一系列树种的叶片对HONO的吸收。由于HONO在化学运输模型中没有得到很好的体现，因此，对HONO源和汇的理解的改进预计将对改进空气质量模型和确定大气中某些温室气体（如甲烷）的寿命产生重要影响。这项工作将大气化学、微生物生态学和建模方面的专业知识与测量HONO土壤排放的独特分析能力相结合。该建议的中心假设是，森林地区冠下氧化氢自由基（HOx）循环和臭氧水平的变化是由土壤排放的HONO （SHONO）和氮氧化物（NO） （SNO）的变化驱动的，这取决于季节、土壤性质、地上植被表面和由微生物-植物相互作用介导的地下氮循环。初步数据表明，在森林环境中，高SNO对冠层下的HOx有显著影响，NOy（活性氮氧化物的总和）通量与森林组成有关，并且NOy通量的空间变异性可以通过森林清查图绘制出整个美国大陆。研究的目的是：(1)建立美国森林shoo的地理空间趋势；(2)开展混交林SHONO野外测量活动；(3)量化叶片和土壤表面对HONO的吸收。该项目将支持一名全职博士后研究员和一名研究生，他们将接受最新科学分析和建模方法的培训。作为印第安纳大学团体暑期研究体验项目的一部分，本科生将直接参与这项研究，该项目为入学的一年级学生提供研究经验和技能，使他们在STEM专业中脱颖而出。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project focuses on land-atmosphere interactions and the mechanisms by which nitrous acid (HONO) and other nitrogen oxides emitted from soils influence the oxidizing capacity of the atmosphere. The experimental plans include the use of growth chambers under controlled conditions combined with field data to study the uptake of HONO onto leaves from a range of tree species that dominate major forested regions across North America. Since HONO is not well represented in chemical transport models, improvements in understanding HONO sources and sinks are expected to have important implications for improving air quality models and for determining the lifetime of some greenhouse gases, such as methane, in the atmosphere.This effort combines expertise in atmospheric chemistry, microbial ecology, and modeling with unique analytical capabilities for measuring HONO soil emissions. The central hypothesis of this proposal is that variations in below-canopy hydrogen oxide radical (HOx) cycling and ozone levels in forested regions are driven by the variability of soil emissions of HONO (SHONO) and nitrogen oxide (NO) (SNO), that depend on season, edaphic properties, aboveground vegetation surfaces, and belowground nitrogen cycling that is mediated by microbe-plant interactions. Preliminary data show that high SNO has a significant impact on below canopy HOx in a forested environment, that NOy (the sum of reactive nitrogen oxides) fluxes are linked to forest composition, and that spatial variability in NOy fluxes can be mapped across the continental U.S. using forest inventory plots. The objectives of the research are to: (1) Establish geospatial trends in SHONO across U.S. forests; (2) Carry out field campaigns to measure SHONO in mixed deciduous forests; and (3) Quantify uptake of HONO by leaf and soil surfaces.The project will support a full-time postdoctoral researcher and a graduate student who will receive training in state-of-the science analytical and modeling methods. Undergraduate students will be directly involved in the research as part of Indiana University’s Groups Summer Research Experience Program, which gives entering first-year students research experience and skills to excel in STEM majors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.