Multi-axis differential optical absorption spectroscopy (MAX-DOAS) and direct sun NO₂ vertical column network data are used to investigate the accuracy of tropospheric NO₂ column measurements of the GOME-2 instrument on the MetOp-A satellite platform and the OMI instrument on Aura. The study is based on 23 MAX-DOAS and 16 direct sun instruments at stations distributed worldwide. A method to quantify and correct for horizontal dilution effects in heterogeneous NO₂ field conditions is proposed. After systematic application of this correction to urban sites, satellite measurements are found to present smaller biases compared to ground-based reference data in almost all cases. We investigate the seasonal dependence of the validation results as well as the impact of using different approaches to select satellite ground pixels in coincidence with ground-based data. In optimal comparison conditions (satellite pixels containing the station) the median bias between satellite tropospheric NO₂ column measurements and the ensemble of MAX-DOAS and direct sun measurements is found to be significant and equal to −34 % for GOME-2A and −24 % for OMI. These biases are further reduced to −24 % and −18 % respectively, after application of the dilution correction. Comparisons with the QA4ECV satellite product for both GOME-2A and OMI are also performed, showing less scatter but also a slightly larger median tropospheric NO₂ column bias with respect to the ensemble of MAX-DOAS and direct sun measurements.

中文翻译：

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使用MAX-DOAS和直接太阳网络观测结果验证GOME-2A和OMI对流层NO ₂柱测量结果

利用多轴差分光学吸收光谱法（MAX-DOAS）和直接的太阳NO ₂ 垂直柱网络数据来研究 MetOp-A卫星平台上的GOME-2仪器和OMI仪器对流层NO ₂柱测量的准确性在光环上。这项研究基于23个MAX-DOAS和16个直接日照仪，分布在全球各地。量化和校正异质NO _2中水平稀释效应的方法建议现场条件。在将此校正系统地应用到城市站点后，几乎在所有情况下，与基于地面的参考数据相比，卫星测量结果都呈现出较小的偏差。我们调查了验证结果的季节性依赖性以及使用不同方法进行验证的影响选择与地面数据一致的卫星地面像素。在最佳比较条件下（包含测站的卫星像素），发现对流层NO ₂柱测量与MAX-DOAS和直射太阳测量的集合之间的中值偏差非常明显， 对于GOME-2A和-24而言为-34％ OMI的％。 在应用稀释校正后，这些偏差分别进一步降低到了 -24  ％和-18％。还对GOME-2A和OMI的QA4ECV卫星产品进行了比较，结果显示散射较小，但对流层中值NO ₂略大 相对于MAX-DOAS和直接太阳测量的整体的列偏差。