Abstract. The chemical composition of the upper troposphere/lower stratosphere region (UTLS) is influenced by horizontal transport of air masses, vertical transport within convective systems and warm conveyor belts, rapid turbulent mixing, as well as photochemical production or loss of species. This results in the formation of the extratropical transition layer (ExTL), which is defined by the vertical structure of CO and has been studied until now mostly by means of trace gas correlations. Here, we extend the analysis to include aerosol particles and derive the sulfate–ozone correlation in central Europe from aircraft in situ measurements during the CAFE-EU (Chemistry of the Atmosphere Field Experiment over Europe)/BLUESKY mission. The mission probed the UTLS during the COVID-19 period with significantly reduced anthropogenic emissions. We operated a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) to measure the chemical composition of non-refractory aerosol particles in the size range from about 40 to 800 nm. In our study, we find a correlation between the sulfate mass concentration and O3 in the lower stratosphere. The correlation exhibits some variability exceeding the mean sulfate–ozone correlation over the measurement period. Especially during one flight, we observed enhanced mixing ratios of sulfate aerosol in the lowermost stratosphere, where the analysis of trace gases shows tropospheric influence. However, back trajectories indicate that no recent mixing with tropospheric air occurred within the last 10 d. Therefore, we analyzed volcanic eruption databases and satellite SO2 retrievals from the TROPOspheric Monitoring Instrument (TROPOMI) for possible volcanic plumes and eruptions to explain the high amounts of sulfur compounds in the UTLS. From these analyses and the combination of precursor and particle measurements, we conclude that gas-to-particle conversion of volcanic SO2 leads to the observed enhanced sulfate aerosol mixing ratios.

中文翻译：

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温带跨对流层顶混合对平流层最低层臭氧与硫酸盐气溶胶相关性的影响


摘要。对流层上层/平流层下层区域（UTLS）的化学成分受到气团水平输送、对流系统和温暖传送带内的垂直输送、快速湍流混合以及光化学产生或物种损失的影响。这导致了温带过渡层（ExTL）的形成，该过渡层由二氧化碳的垂直结构定义，迄今为止主要通过痕量气体相关性进行研究。在这里，我们将分析扩展到包括气溶胶颗粒，并通过 CAFE-EU（欧洲上空大气化学现场实验）/BLUESKY 任务期间飞机的现场测量得出中欧的硫酸盐-臭氧相关性。该任务在 COVID-19 期间对 UTLS 进行了探测，人为排放量显着减少。我们使用紧凑型飞行时间气溶胶质谱仪 (C-ToF-AMS) 来测量尺寸范围约为 40 至 800 nm 的非难熔气溶胶颗粒的化学成分。在我们的研究中，我们发现平流层下部硫酸盐质量浓度与 O3 之间存在相关性。该相关性表现出一些变化，超过了测量期间平均硫酸盐-臭氧相关性。特别是在一次飞行期间，我们观察到平流层最低层硫酸盐气溶胶的混合比例增加，痕量气体的分析表明对流层的影响。然而，向后轨迹表明在过去 10 天内没有发生与对流层空气的混合。因此，我们分析了火山喷发数据库和从对流层监测仪器 (TROPOMI) 获取的卫星 SO2 数据，寻找可能的火山羽流和喷发，以解释 UTLS 中存在大量硫化合物。 根据这些分析以及前体和颗粒测量的结合，我们得出结论，火山 SO2 的气体到颗粒的转化导致观察到的硫酸盐气溶胶混合比增强。