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Key chemical NOx sink uncertainties and how they influence top-down emissions of nitrogen oxides

机译：关键化学NOx汇不确定性以及它们如何影响自上而下的氮氧化物排放

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Triggered by recent developments from laboratory and field studies regarding major NO_x sink pathways in the troposphere, this study evaluates the influence of chemical uncertainties in NO_x sinks for global NO_x distributions calculated by the IMAGESv_2 chemistry-transport model, and quantifies their significance for top-down NO_x emission estimates. Our study focuses on five key chemical parameters believed to be of primary importance, more specifically, the rate of the reaction of NO_2 with OH radicals, the newly identified HNO 3-forming channel in the reaction of NO with HO_2, the reactive uptake of N_2O5 and HO_2 by aerosols, and the regeneration of OH in the oxidation of isoprene. Sensitivity simulations are performed to estimate the impact of each source of uncertainty. The model calculations show that, although the NO_2+OH reaction is the largest NO_x sink globally accounting for ca. 60% of the total sink, the reactions contributing the most to the overall uncertainty are the formation of HNO_3 in NO+HO_2, leading to NO_x column changes exceeding a factor of two over tropical regions, and the uptake of HO _2 by aqueous aerosols, in particular over East and South Asia. Emission inversion experiments are carried out using model settings which either minimise (MINLOSS) or maximise (MAXLOSS) the total NO x sink, both constrained by one year of OMI NO_2 column data from the DOMINO v_2 KNMI algorithm. The choice of the model setup is found to have a major impact on the top-down flux estimates, with 75% higher emissions for MAXLOSS compared to the MINLOSS inversion globally. Even larger departures are found for soil NO (factor of 2) and lightning (1.8). The global anthropogenic source is better constrained (factor of 1.57) than the natural sources, except over South Asia where the combined uncertainty primarily associated to the NO+HO_2 reaction in summer and HO_2 uptake by aerosol in winter lead to top-down emission differences exceeding a factor of 2. Evaluation of the emission optimisation is performed against independent satellite observations from the SCIAMACHY sensor, with airborne NO_2 measurements of the INTEX-A and INTEX-B campaigns, as well as with two new bottom-up inventories of anthropogenic emissions in Asia (REASv_2) and China (MEIC). Neither the MINLOSS nor the MAXLOSS setup succeeds in providing the best possible match with all independent datasets. Whereas the minimum sink assumption leads to better agreement with aircraft NO_2 profile measurements, consistent with the results of a previous analysis (Henderson et al., 2012), the same assumption leads to unrealistic features in the inferred distribution of emissions over China. Clearly, although our study addresses an important issue which was largely overlooked in previous inversion exercises, and demonstrates the strong influence of NO_x loss uncertainties on top-down emission fluxes, additional processes need to be considered which could also influence the inferred source.
机译：由对流层中主要NO_x汇途径的实验室和现场研究的最新进展触发，本研究评估了IMAGESv_2化学迁移模型计算出的NO_x汇化学不确定性对全球NO_x分布的影响，并量化了其对自上而下的意义NO_x排放估算。我们的研究集中在五个最重要的化学关键参数上，更具体地说，是NO_2与OH自由基的反应速率，在NO与HO_2反应中新发现的HNO 3形成通道，N_2O5的反应性吸收气溶胶产生的HO_2和HO_2，以及异戊二烯氧化过程中OH的再生。进行灵敏度仿真以估计每个不确定性源的影响。模型计算表明，尽管NO_2 + OH反应是全球最大的NO_x汇，但约占在总汇的60％中，对总体不确定性影响最大的反应是在NO + HO_2中形成HNO_3，导致热带地区的NO_x色谱柱变化超过两倍，以及水气溶胶对HO _2的吸收，特别是在东亚和南亚。 排放反演实验使用最小化（MINLOSS）或最大化（MAXLOSS）总NOx吸收量的模型设置进行，二者均受到来自DOMINO v_2 KNMI算法的OMI NO_2色谱柱数据的限制。发现模型设置的选择对自顶向下的通量估算值有重大影响，与全球的MINLOSS反演相比，MAXLOSS的排放量高出75％。土壤NO（2的因子）和闪电（1.8）的偏差更大。全球人为源比自然源受到更好的约束（系数为1.57），南亚除外，南亚地区的不确定性主要与夏季的NO + HO_2反应和冬季的气溶胶吸收引起的综合不确定性导致自上而下的排放差异超过因子是2。 排放优化的评估是根据SCIAMACHY传感器的独立卫星观测结果进行的，对INTEX-A和INTEX-B战役的机载NO_2测量，以及两个新的底部亚洲（REASv_2）和中国（MEIC）的人为排放量清单。 MINLOSS或MAXLOSS设置都无法成功提供与所有独立数据集的最佳匹配。最低汇假设与飞机NO_2剖面测量结果更好地吻合，这与先前的分析结果一致（Henderson等，2012），但相同的假设导致推断的中国排放分布特征不切实际。显然，尽管我们的研究解决了一个重要的问题，该问题在以前的反演练习中基本上被忽略，并且证明了NO_x损失不确定性对自上而下的排放通量的强大影响，但仍需要考虑可能影响推断来源的其他过程。

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