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

该项目重点研究陆地与大气的相互作用以及土壤中排放的亚硝酸（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并结合现场数据来研究北美主要森林地区的一系列树种的叶子对 HONO 的吸收。由于 HONO 在化学输运模型中没有得到很好的体现，因此加深对 HONO 源和汇的了解预计将对改善空气质量模型和确定某些温室气体（例如甲烷）在大气中的寿命产生重要影响。这项工作结合了大气化学、微生物生态学和建模方面的专业知识以及测量 HONO 土壤排放的独特分析能力。该提案的中心假设是，森林地区冠层下氧化氢自由基（HOx）循环和臭氧水平的变化是由HONO（SHONO）和氮氧化物（NO）（SNO）土壤排放的可变性驱动的，这取决于季节、土壤特性、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，高 SNO 对森林环境中的冠层以下 HOx 有重大影响，NOy（活性氮氧化物的总和）通量与森林组成相关，并且可以使用森林清查图绘制美国大陆 NOy 通量的空间变异性。研究的目标是： (1) 确定美国森林 SHONO 的地理空间趋势； (2) 开展实地活动，测量落叶混交林中的 SHONO； (3) 量化叶子和土壤表面对 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计划的一部分，本科生将直接参与研究，该计划为一年级学生提供研究经验和技能，以在 STEM 专业中脱颖而出。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力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.