Nitrogen Oxide Chemistry: Connecting Ambient Concentrations to Mechanisms of Emission, Oxidaton and Aerosol Formation

该项目支持对2007年和2009年生物圈对气溶胶和光化学实验（BEARPEX）的通量和梯度测量结果进行综合解释。总体目标是提高对大气和森林之间氮交换的机制理解。氮氧化物通过NOx （NO + NO2）循环直接控制对流层O3的催化生成，通过HOx （OH + HO2）循环的终止反应和相关的高级氮氧化物的生成间接控制对流层O3的催化生成。大气-生物圈NOy交换也影响区域和全球尺度的NOy收支、生态系统生产力和碳循环。对对流层的物理化学演化和涉及生态系统的相关反馈的可靠预测能力要求了解氮氧化物循环的主要途径并在模式中可靠地实施。在以往成果的基础上，本项目将研究调节森林NO2补偿点的因素，即低于NO2从森林排放而高于NO2沉积到森林的大气混合比。BEARPEX 2007和2009实验的设计，部分是为了提供这些二氧化氮交换过程性质的定量约束。通过森林冠层测量NO和NO2混合比的垂直梯度及其相应的进出冠层通量。测定了森林土壤中NO的通量。这些结果为补偿点提供了独立的证据，但从每个点推断出的实际值各不相同。此外，2004年在同一地点使用类似技术测量的NO和NO2通量的补偿点高出3倍，这表明大气-森林交换的性质可能随环境NOx混合比率的长期时间变化而变化。除氮氧化物外，2009年BEARPEX期间较高氮氧化物的交换通量与2004年的测量值有很大差异。这个项目将综合这些不同的数据和相关的过程级约束。结果将根据理论方法解释，包括修正布朗宁分析和详细的模型计算。总的目标是根据现有的观测限制，对调节大气和森林之间氮交换的因素形成连贯的机制理解。该项目将有助于培养研究生（包括两名女性）和本科生。它还将通过与Chabot空间和科学中心的合作，促进K-12科学教育，Chabot空间和科学中心是奥克兰学区的一个强大的当地博物馆。最后，结果将促进对有关空气质量和气候的政策决策的科学基础的理解。研究结果将在科学文献中公布，通过各种外展媒体向更广泛的受众公布，并直接向加州湾区空气质量管理区和加州空气资源委员会的监管机构公布。

This project supports an integrated interpretation of flux and gradient measurements from the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) during 2007 and 2009. The overall goal is to improve mechanistic understanding of nitrogen exchange between the atmosphere and forests. Nitrogen oxides control the catalytic production of tropospheric O3 directly via NOx (NO + NO2) cycling and indirectly via termination reactions of the HOx (OH + HO2) cycle and associated production of higher oxides of nitrogen. The atmosphere-biosphere exchange of NOy (sum of oxidized N species) also affects NOy budgets on regional and global scales, ecosystem productivity, and carbon cycling. A reliable predictive capability for the physicochemical evolution of the troposphere and related feedbacks involving ecosystems requires that major pathways in the cycling of nitrogen oxides be understood and reliably implemented in models. Building on past results, this project will investigate factors regulating the forests NO2 compensation point, the atmospheric mixing ratio below which NO2 is emitted from the forest and above which NO2 is deposited to the forest. The BEARPEX 2007 and 2009 experiments were designed, in part, to provide quantitative constraints on the nature of these NO2 exchange processes. Vertical gradients in NO and NO2 mixing ratios through the forest canopy were measured in parallel with their corresponding fluxes into and out of the canopy. Fluxes of NO from forest soils were also quantified. These results provide independent evidence for a compensation point but actual values inferred from each vary. In addition, NO and NO2 fluxes measured using similar techniques during a 2004 experiment at the same location yielded a factor of 3 greater compensation point, which suggests that the nature of atmosphere-forest exchange may vary as a function of long-term temporal changes in ambient NOx mixing ratios. In addition to NOx, exchange fluxes of higher oxides of nitrogen during BEARPEX 2009 diverged substantially from those measured in 2004. This project will synthesize these various data and associated process-level constraints. Results will be interpreted based on theoretical approaches including modified Browning analysis and detailed model calculations. The overall goal is to develop a coherent mechanistic understanding of factors regulating nitrogen exchange between the atmosphere and forests based on the available observational constraints. The project will contribute to the training graduate students, including two women, and undergraduate students. It will also foster K-12 science education through collaboration with the Chabot Space and Science Center, a local museum with a strong presence in the Oakland school district. Finally, results will advance understanding of the scientific basis for policy decisions regarding air quality and climate. Findings will be communicated in the scientific literature, to a more general audience through various outreach media, and directly to regulators in California at both the Bay Area Air Quality Management District and the California Air Resources Board.