RII Track-4:NSF: Assessment of Multiscale Air Quality Model (CMAQ) Representation of Spatiotemporal Atmospheric Nitrate Chemical Production in New England

硝酸盐是大气中的一种重要成分，来自于对空气质量、酸沉降和气候有重要影响的氮氧化物排放前体。 氮氧化物排放主要由人类活动主导，通常与化石燃料燃烧有关，由于有效的监管，过去几十年来美国各地的氮氧化物排放量大幅下降。 然而，硝酸盐的大气沉积仍然是一个重要的环境压力。 大气化学传输模型，这是常用的，以帮助指导政策，有困难再现观察到的大气硝酸盐浓度和沉积，导致不明确的指导方针，以改善现有的清洁空气法案二级标准。这种分歧可能与大气硝酸盐的复杂生产机制有关，需要更深入地了解硝酸盐大气化学，以更好地预测氮沉降的大气负担。 在该项目中，PI将与美国环保署研究三角园区的科学家合作，利用新型氧同位素示踪技术（Δ 17 O）评估和改进常用的大气化学和传输模型对大气硝酸盐形成的表示。 利用三维大气化学和传输模型，该项目将提高PI的研究专业知识，并有助于研究生的培训和学习。 该项目将在PI和东道主科学家之间建立新的长期合作关系。 项目成果将包括在布朗大学建立第一个大气化学和运输模型，该模型将用于布朗大学PI和其他合作者未来的研究项目，提高罗得岛的研究能力。氧稳定同位素组成（Δ 17 O）已被证明能对大气硝酸盐的产生机制提供定量的观测约束。 这是因为关键的大气氧化剂具有独特的Δ 17 O特征（或“指纹”），其结合在由前体氮氧化物排放物的氧化产生的产物硝酸盐中。 这项工作将使用社区多尺度空气质量模型（CMAQ）评估2005-2017年新英格兰时空大气硝酸盐生产的化学代表性。 模型模拟将使用高分辨率的美国域进行，大气硝酸盐形成途径将被标记，并用于计算定量表达硝酸盐生产机制的氧稳定同位素组成。 模型输出将用于与新英格兰大气硝酸盐的详细时空Δ 17 O观测结果进行比较，利用先前NSF支持的详细Δ 17 O数据来测试和改进新英格兰硝酸盐化学的大气化学模型表示。 该项目的目标包括评估大气硝酸盐的时空形成的化学表征，以及在氮氧化物排放显著减少的时期内美国东北部硝酸和颗粒硝酸盐之间的差异。 最终，该项目将使人们更好地理解减排对氮的大气循环的作用及其与大气成分、空气质量和酸沉降的联系。该奖项反映了NSF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。

Nitrate is a key component of the atmosphere that derives from precursor nitrogen oxide emissions that have important implications for air quality, acid deposition, and climate. Nitrogen oxide emissions are dominated by anthropogenic activities, typically associated with fossil-fuel combustion, which has dramatically declined across the US over the last several decades due to effective regulations. Yet, atmospheric deposition of nitrate remains a significant environmental stressor. Atmospheric chemistry transport models, which are commonly utilized to help guide policy, have difficulties reproducing observed atmospheric nitrate concentrations and deposition, resulting in unclear guidelines to improve existing Clean Air Act Secondary Standards. This disagreement may be related to complicated production mechanisms of atmospheric nitrate, requiring a deeper understanding of nitrate atmospheric chemistry to better predict the atmospheric burden of nitrogen deposition. In this project, the PI will partner with scientists from the US EPA Research Triangle Park to evaluate and improve upon a commonly utilized atmospheric chemistry and transport model’s representation of atmospheric nitrate formation utilizing a novel oxygen isotope tracer technique (Δ17O). Using a three-dimensional atmospheric chemistry and transport model, this project will enhance the PI’s research expertise and contribute to the training and learning of a graduate student. This project will establish new and long-lasting collaborations between the PI and host scientists. Project outcomes will include establishing the first atmospheric chemistry and transport model at Brown University that will be utilized in future research projects by the PI and other collaborators at Brown, enhancing Rhode Island's research capabilities. The oxygen stable isotopic composition (Δ17O) has been proven to provide quantitative observational constraints on the production mechanisms of atmospheric nitrate. This is because key atmospheric oxidants have distinctive Δ17O signatures (or "fingerprints") incorporated in the product nitrate derived from the oxidation of precursor nitrogen oxide emissions. This work will evaluate the chemical representation of spatiotemporal atmospheric nitrate production in New England from 2005-2017 using the Community Multiscale Air Quality Model (CMAQ). Model simulations will be conducted using a high-resolution US domain, and atmospheric nitrate formation pathways will be tagged and used to calculate the oxygen stable isotopic composition that quantitatively expresses nitrate production mechanisms. The model output will be used to compare with detailed spatiotemporal Δ17O observations of atmospheric nitrate in New England, leveraging detailed Δ17O data from prior NSF support to test and improve upon atmospheric chemistry model representation of nitrate chemistry in New England. The goals of this project include evaluating the chemical representation of the spatiotemporal formation of atmospheric nitrate and differences between nitric acid and particulate nitrate across the northeastern US during a period of significant reductions in nitrogen oxide emissions. Ultimately, this project will lead to a better understanding of the role of emission reductions on the atmospheric cycle of nitrogen and its connection to atmospheric composition, air quality, and acid deposition.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.