Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measured the middle-infrared limb emission spectrum of the atmosphere from 2002 to 2012 on board ENVISAT, a polar-orbiting satellite. Recently, the European Space Agency (ESA) completed the final reprocessing of MIPAS measurements, using Version 8 of the Level 1 and Level 2 processors, which include more accurate models, processing strategies and auxiliary data. The list of retrieved gases has been extended, it now includes a number of new species with weak emission features in the MIPAS spectral range. The new retrieved trace species include carbonyl chloride (COCl₂), also called phosgene. Due to its toxicity, its use has been reduced over the years, however it is still used by chemical industries for sevaeral applications. Besides its direct injection in the troposphere, stratospheric phosgene is mainly produced from the photolysis of CCl₄, a molecule present in the atmosphere because of human activity. Since phosgene has a long stratospheric lifetime, it must be carefully monitored as it is involved in the ozone destruction cycles, especially over the winter polar regions. In this paper we exploit the ESA MIPAS Version 8 data in order to discuss the phosgene distribution, variability and trends in the middle and lower stratosphere and in the upper troposphere. The zonal averages show that phosgene volume mixing ratio is larger in the stratosphere, with a peak of 40 pptv between 50 and 30 hPa at equatorial latitudes, while at middle and polar latitudes it varies from 10 to 25 pptv. A moderate seasonal variability is observed in polar regions, mostly between 80 and 50 hPa. The comparison of MIPAS/ENVISAT COCl₂ v.8 profiles with the ones retrieved from MIPAS/balloon and ACE-FTS measurements highlights a negative bias of about 2 pptv, mainly in polar and mid-latitude regions. Part of this bias is attributed to the fact that the ESA Level 2 v.8 processor uses an updated spectroscopic database. For the trend computation, a fixed pressure grid is used to interpolate the phosgene profiles and, for each pressure level, VMR monthly averages are computed in pre-defined 10°-wide latitude bins. Then, for each latitudinal bin and pressure level, a regression model has been fitted to the resulting time-series in order to derive the atmospheric trends. We find that the phosgene trends are different in the two hemispheres. The analysis shows that the stratosphere of the Northern Hemisphere is characterised by a negative trend, of about −7 pptv/decade, while in the Southern Hemisphere phosgene mixing ratios increase with a rate of the order of +4 pptv/decade. In the upper troposphere a positive trend is found in both hemispheres.

中文翻译：

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来自 MIPAS ESA v8 数据的光气分布：相互比较和趋势

摘要。用于无源大气探测的迈克尔逊干涉仪 (MIPAS) 测量了 2002 年至 2012 年在 ENVISAT（极轨卫星）上的大气中红外临边发射光谱。最近，欧洲航天局 (ESA) 使用 Level 1 和 Level 2 处理器的第 8 版完成了 MIPAS 测量的最终再处理，其中包括更准确的模型、处理策略和辅助数据。回收的气体清单已扩展，现在包括许多在 MIPAS 光谱范围内具有弱发射特征的新物种。新回收的痕量物质包括碳酰氯 (COCl ₂ )，也称为光气. 由于它的毒性，多年来它的使用已经减少，但是它仍然被化学工业用于几种应用。除直接注入对流层外，平流层光气主要由CCl ₄光解产生，一种由于人类活动而存在于大气中的分子。由于光气具有较长的平流层寿命，因此必须对其进行仔细监测，因为它参与臭氧破坏循环，尤其是在冬季极地地区。在本文中，我们利用 ESA MIPAS 第 8 版数据来讨论平流层中、下层和对流层上层的光气分布、变异性和趋势。纬向平均值表明光气体积混合比在平流层较大，在赤道纬度50-30 hPa之间达到40 pptv的峰值，而在中纬度和极地纬度为10-25 pptv。在极地地区观察到适度的季节性变化，主要在 80 到 50 hPa 之间。MIPAS/ENVISAT COCl ₂的比较v.8 剖面与从 MIPAS/气球和 ACE-FTS 测量中检索到的剖面突出了大约 2 pptv 的负偏差，主要是在极地和中纬度地区。这种偏差的部分原因是 ESA Level 2 v.8 处理器使用更新的光谱数据库。对于趋势计算，固定压力网格用于插入光气剖面，并且对于每个压力水平，VMR 月平均值在预定义的 10° 宽纬度箱中计算。然后，对于每个纬度区间和压力水平，回归模型已被拟合到结果时间序列中，以推导出大气趋势。我们发现两个半球的光气趋势不同。分析表明，北半球平流层呈负趋势，约为-7 pptv/decade，而在南半球，光气混合比率以 +4 pptv/decade 的速度增加。在对流层上层，两个半球都出现了积极的趋势。