The Ozone Monitoring Instrument (OMI) has been providing global observations of SO₂ pollution since 2004. Here we introduce the new anthropogenic SO₂ vertical column density (VCD) dataset in the version 2 OMI SO₂ product (OMSO2 V2). As with the previous version (OMSO2 V1.3), the new dataset is generated with an algorithm based on principal component analysis of OMI radiances but features several updates. The most important among those is the use of expanded lookup tables and model a priori profiles to estimate SO₂ Jacobians for individual OMI pixels, in order to better characterize pixel-to-pixel variations in SO₂ sensitivity including over snow and ice. Additionally, new data screening and spectral fitting schemes have been implemented to improve the quality of the spectral fit. As compared with the planetary boundary layer SO₂ dataset in OMSO2 V1.3, the new dataset has substantially better data quality, especially over areas that are relatively clean or affected by the South Atlantic Anomaly. The updated retrievals over snow/ice yield more realistic seasonal changes in SO₂ at high latitudes and offer enhanced sensitivity to sources during wintertime. An error analysis has been conducted to assess uncertainties in SO₂ VCDs from both the spectral fit and Jacobian calculations. The uncertainties from spectral fitting are reflected in SO₂ slant column densities (SCDs) and largely depend on the signal-to-noise ratio of the measured radiances, as implied by the generally smaller SCD uncertainties over clouds or for smaller solar zenith angles. The SCD uncertainties for individual pixels are estimated to be ∼ 0.15–0.3 DU (Dobson units) between ∼ 40^∘ S and ∼ 40^∘ N and to be ∼ 0.2–0.5 DU at higher latitudes. The uncertainties from the Jacobians are approximately ∼ 50 %–100 % over polluted areas and are primarily attributed to errors in SO₂ a priori profiles and cloud pressures, as well as the lack of explicit treatment for aerosols. Finally, the daily mean and median SCDs over the presumably SO₂-free equatorial east Pacific have increased by only ∼ 0.0035 DU and ∼ 0.003 DU respectively over the entire 15-year OMI record, while the standard deviation of SCDs has grown by only ∼ 0.02 DU or ∼ 10%. Such remarkable long-term stability makes the new dataset particularly suitable for detecting regional changes in SO₂ pollution.

中文翻译：

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第2版​​臭氧监测仪器SO ₂产品（OMSO2 V2）：新的人为SO ₂垂直柱密度数据集

自2004年以来，臭氧监测仪器（OMI）一直在全球范围内观察SO ₂污染。在此，我们在版本2 OMI SO ₂产品（OMSO2 V2）中引入了新的人为SO ₂垂直柱密度（VCD）数据集。与以前的版本（OMSO2 V1.3）一样，新数据集是使用基于OMI辐射的主成分分析的算法生成的，但具有一些更新。其中最重要的是使用扩展的查找表和建模先验轮廓来估计单个OMI像素的SO ₂雅可比矩阵，以便更好地表征SO ₂的像素间差异 灵敏度包括在冰雪上。另外，已经实施了新的数据筛选和光谱拟合方案以提高光谱拟合的质量。与OMSO2 V1.3中的行星边界层SO ₂数据集相比，新数据集具有更好的数据质量，尤其是在相对较干净或受南大西洋异常影响的区域。在高纬度上更新的雪/冰反演可产生更现实的SO ₂季节变化，并在冬季提高了对源的敏感性。进行了误差分析，以从光谱拟合和雅可比计算中评估SO ₂ VCD的不确定性。光谱拟合的不确定性反映在SO _2中倾斜列密度（SCD）很大程度上取决于测得辐射的信噪比，这通常是由于云上较小的SCD不确定性或较小的太阳天顶角所暗示。对于各个像素的SCD的不确定性估计为 〜 之间0.15-0.3 DU（多布森单位）〜  40 ^∘  S和〜  40 ^∘  N和为 〜  0.2-0.5 DU在高纬度地区。雅可比人的不确定性 在污染地区大约为50％–100％，主要归因于SO _2的误差先验概况和云压，以及缺乏对气溶胶的明确处理。最后，在大概SO每日平均数和中位数的SCD ₂ -免费赤道东太平洋地区仅增长了〜  0.0035 DU和 〜  0.003 DU分别在整个15年的OMI记录，而发生SCD的标准差已经只有大〜  0.02 DU或〜10  ％。如此出色的长期稳定性使新数据集特别适用于检测SO ₂ 污染的区域变化。