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Sensitivity to grid resolution in the ability of a chemical transport model to simulate observed oxidant chemistry under high-isoprene conditions

机译:在化学传输模型能够模拟高异戊二烯条件下观察到的氧化剂化学过程中对网格分辨率的敏感性

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摘要

Formation of ozone and organic aerosol in continental atmospheres depends onwhether isoprene emitted by vegetation is oxidized by the high-NO pathway(where peroxy radicals react with NO) or by low-NO pathways (where peroxyradicals react by alternate channels, mostly with HO). We used mixedlayer observations from the SEACRS aircraft campaign over the SoutheastUS to test the ability of the GEOS-Chem chemical transport model at differentgrid resolutions (0.25°  ×  0.3125°,2°  ×  2.5°, 4°  ×  5°) tosimulate this chemistry under high-isoprene, variable-NO conditions.Observations of isoprene and NO over the Southeast US show a negativecorrelation, reflecting the spatial segregation of emissions; this negativecorrelation is captured in the model at0.25°  ×  0.3125° resolution but not at coarserresolutions. As a result, less isoprene oxidation takes place by thehigh-NO pathway in the model at 0.25°  ×  0.3125°resolution (54 %) than at coarser resolution (59 %). The cumulativeprobability distribution functions (CDFs) of NO, isoprene, and ozoneconcentrations show little difference across model resolutions and goodagreement with observations, while formaldehyde is overestimated at coarseresolution because excessive isoprene oxidation takes place by thehigh-NO pathway with high formaldehyde yield. The good agreement ofsimulated and observed concentration variances implies that smaller-scalenon-linearities (urban and power plant plumes) are not important on theregional scale. Correlations of simulated vs. observed concentrations do notimprove with grid resolution because finer modes of variability areintrinsically more difficult to capture. Higher model resolution leads todecreased conversion of NO to organic nitrates and increased conversionto nitric acid, with total reactive nitrogen oxides (NO) changing littleacross model resolutions. Model concentrations in the lower free troposphereare also insensitive to grid resolution. The overall low sensitivity ofmodeled concentrations to grid resolution implies that coarse resolution isadequate when modeling continental boundary layer chemistry for globalapplications.
机译:大陆大气中臭氧和有机气溶胶的形成取决于植被释放的异戊二烯是通过高NO途径(过氧自由基与NO反应)还是通过低NO途径(过氧自由基通过替代途径(主要是HO)反应)氧化。我们使用东南美国SEACRS飞机战役中的混合层观测来测试GEOS-Chem化学迁移模型在不同网格分辨率(0.25°××0.3125°,2°××2.5°,4°××5°)下的能力,以模拟这种化学反应高异戊二烯,NO可变的条件。美国东南部的异戊二烯和NO的观测值显示负相关,反映了排放物的空间隔离。在模型中以0.25°××0.3125°的分辨率捕获了这种负相关,但在较粗的分辨率下却没有。结果,模型中高NO途径在0.25°××0.3125°分辨率(54 %%)下发生的异戊二烯氧化反应比在较粗分辨率(59 %%)下发生的异戊二烯氧化反应少。 NO,异戊二烯和臭氧浓度的累积概率分布函数(CDF)在模型分辨率和观察值之间显示出很小的差异,而在粗略分辨率下高估了甲醛,因为高NO途径会通过甲醛含量高的高NO途径发生过量的异戊二烯氧化。模拟和观察到的浓度变化的良好一致性表明,较小尺度的非线性(城市和电厂烟羽)在区域尺度上并不重要。网格分辨率并不能改善模拟浓度与观测浓度之间的相关性,因为从本质上讲,更精细的可变模式很难捕获。较高的模型分辨率导致NO向有机硝酸盐的转化率降低,而向硝酸的转化率提高,而在整个模型分辨率下,总反应性氮氧化物(NO)的变化均很小。自由对流层下部的模型浓度对网格分辨率也不敏感。建模浓度对网格分辨率的总体敏感性较低,这意味着在为全球应用建模大陆边界层化学时,粗分辨率就足够了。

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