Lenard Lukas Röder

Recently, global mean methane concentrations have increased strongly. Methane is one of the most important greenhouse gases and plays a key role in atmospheric chemistry. Especially, due to its long lifetime of approx. 10 years and its significant effect on Earth’s climate change, a detailed knowledge of its source regions and their temporal evolution is crucial.In this study, we present a unique data set of methane measured in situ over the Amazon rainforest region during the wet season in the CAFE Brazil (Chemistry of the Atmosphere Field Experiment) aircraft campaign from December 2022 to January 2023 in Manaus, Brazil. Methane was measured with an infrared quantum cascade laser absorption spectrometer on board the High Altitude and LOng-range aircraft (HALO). These observations show enhanced concentrations of methane in and above the boundary layer of the Amazon rainforest. Locally, dry air mixing ratios of up to approx. 2100 ppbv could be measured up to 4 km of altitude. Detailed analysis shows only a small contribution from anthropogenic sources. Especially over permanent wetlands and deforested areas, the methane concentrations were enhanced. Furthermore, the data has been compared to satellite measurements from the National Oceanic and Atmospheric Administration (NOAA), indicating good agreement in the free troposphere. Nevertheless, the mean levels directly above the Amazon rainforest are approx. 100 ppbv higher than the global background. Moreover, a global distribution based on airborne data from several campaigns (PHILEAS 2023, CAFE Brazil 2022/23, SouthTrac 2019, CAFE Africa 2018, WISE 2017, ATom 2016/17, OMO 2015, ESMVal 2012) shows that the methane surface concentrations over the Amazon rainforest has a local maximum. This calls for more detailed investigations of methane near the surface in the Amazon and raises an important question: Have we underestimated the Amazon rainforest as a significant source of the global methane budget?

The composition of the upper troposphere/lower stratosphere region (UTLS) is influenced by long-range or regional transport in the troposphere and stratosphere, 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, which has been defined by the vertical structure of CO profiles and studied by now mostly by means of trace gas correlations. Here, we extend the analysis to aerosol particles and derive the ozone to sulfate aerosol correlation in Central Europe from aircraft in-situ measurements during the CAFE-EU/BLUESKY mission in May and June 2020. During the campaign two research aircraft, i.e., DLR-HALO (High Altitude and Long Range Research Aircraft) and DLR-Falcon, were deployed covering an altitude range from the planetary boundary layer up to 14 km altitude and thus probing the UTLS during the COVID-19 period with significant 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 addition to the C-ToF-AMS data, we use trace gas measurements from both HALO and DLR-Falcon.In our study, we find a correlation between the ozone mixing ratio (O3) and the sulfate mass concentration in the lower stratosphere, between 10 and 14 km for all flights. The correlation is not constant with time but exhibits some variability over the two-week period of the campaign exceeding the background sulfate to ozone correlation. Especially during one flight, we observed enhanced mixing ratios of sulfate aerosol in the lowermost stratosphere, where the analysis of trace gases, such as CO, SO2, H2O, O3 and HNO3 show tropospheric influence during this time. Also, back trajectories indicate, that no recent mixing with tropospheric air occurred within the last 10 days. In addition, we analyzed satellite SO2 retrievals from TROPOMI for volcanic plumes and eruptions. These satellite observations show enhanced volcanic activities in April 2020 on Kamchatka, Russia, with at least one explosive eruption of the Sheveluch volcano reaching the tropopause region and some minor eruptions of different volcanoes into the free troposphere. From these findings, we conclude that gas-to-particle conversion of volcanic SO2 leads to the observed enhanced sulfate aerosol mixing ratios.

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.

Here, we report on the development of a new quantum cascade laser infrared absorption spectroscopy (QLAS) instrument, the Airborne Tropospheric Tracer In-situ Laser Absorption spectrometer (ATTILA), for atmospheric trace-gas measurements on board of the German High-Altitude Long-range Observatory (HALO) aircraft. Its small and light design makes it suitable for airborne measurements up to approximately 150 hPa of ambient pressure (13–14 km). The dual laser instrument can measure several trace gases simultaneously in two 36.4 m path astigmatic Herriott cells with a data acquisition frequency of 1 Hz. We describe the measurement method and the data acquisition of ATTILA and its in-flight performance by focusing on potential sources of influences on the signal, which we investigated with a dedicated test flight during which the instrument sampled from a constant source. We show that linear critical influences associated with challenging movement patterns can be corrected afterwards, while nonlinear limitations can be minimized by appropriate calibration frequencies and integrated time intervals. During the recent aircraft campaign CAFE Brazil (Chemistry of the Atmosphere Field Experiment in Brazil) from December 2022 to January 2023, carbon monoxide (CO) measurements from ATTILA show a good agreement of a R² of 0.89 with simultaneous CO measurements from an established IR spectrometer for airborne measurements, the TRacer In Situ TDLAS (tunable diode laser absorption spectroscopy) for Atmospheric Research (TRISTAR), at a 10 s time resolution. First dynamical characteristics and tracer distributions of CO and methane (CH₄) over the Amazon rainforest can be identified with ATTILA measurements with a total measurement uncertainty of 10.1 % and 17.5 % for calibration gas mixing ratios of 153 and 1990 ppbv and a data accuracy of 0.3 % and 5.5 % for a data acquisition frequency of 1 Hz for CO and CH₄, respectively.

State-of-the-art neural network architectures in image classification and natural language processing were applied to interference fringe reduction in absorption spectroscopy by interpreting the data structure accordingly. A model was designed for temporal interpolation of background spectra and a different model was created for gas concentration fitting. The networks were trained on experimental data provided by a wavelength modulation spectroscopy instrument and the best performing architectures were analyzed further to evaluate generalization performance, robustness and transferability. A BERT-styled fitter achieved the best performance on the validation set and reduced the mean squared error of fitted amplitude by 99.5%. However, analysis of the de-noising behavior showed large biases. A U-Net styled convolutional neural network reduced the mean squared error of the interpolation by 93.2%. Evaluation on a test set provided evidence that the combination of model interpolation and linear fitting was robust and the detection limit was improved by 52.4%. Transferring the trained interpolator model to a different spectrometer setup showed no chaotic out-of-distribution effects. Additional fine-tuning further increased the performance. Neural network architectures cannot be generally applied to all absorption spectroscopy tasks. However, given the right task and the data representation, robust performance increase is achievable.

The composition of the upper troposphere/lower stratosphere region (UTLS) is influenced by horizontal transport, 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 has been defined by the vertical structure of CO profiles and studied by now mostly by means of trace gas correlations. Here, we extend the analysis to aerosol particles and derive the ozone to sulfate aerosol correlation in Central Europe from aircraft in-situ measurements during the CAFE-EU/BLUESKY mission, probing the UTLS during the COVID-19 period with significant 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 ozone mixing ratio (O₃) and the sulfate mass concentration in the lower stratosphere. The correlation exhibits some variability over the measurement period exceeding the background sulfate to ozone correlation. 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. Also, back trajectories indicate, that no recent mixing with tropospheric air occurred within the last 10 days. In addition, we analyzed satellite SO₂ retrievals from TROPOMI for volcanic plumes and eruptions. From these analyses, we conclude that gas-to-particle conversion of volcanic SO₂ leads to the observed enhanced sulfate aerosol mixing ratios.

The composition of the upper troposphere/lower stratosphere region (UTLS) is influenced by horizontal transport, 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 has been defined by the vertical structure of CO profiles and studied by now mostly by means of trace gas correlations. Here, we extend the analysis to aerosol particles and derive the ozone to sulfate aerosol correlation in Central Europe from aircraft in-situ measurements during the CAFE-EU/BLUESKY mission, probing the UTLS during the COVID-19 period with significant 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 ozone mixing ratio (O₃) and the sulfate mass concentration in the lower stratosphere. The correlation exhibits some variability over the measurement period exceeding the background sulfate to ozone correlation. 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. Also, back trajectories indicate, that no recent mixing with tropospheric air occurred within the last 10 days. In addition, we analyzed satellite SO₂ retrievals from TROPOMI for volcanic plumes and eruptions. From these analyses, we conclude that gas-to-particle conversion of volcanic SO₂ leads to the observed enhanced sulfate aerosol mixing ratios.

Here, we report the development of a new Quantum cascade Laser infrared Absorption Spectroscopy (QLAS) instrument, the Airborne Tropospheric Tracer In-situ Laser Absorption spectrometer (ATTILA), for atmospheric trace gas measurements on board of the German High-Altitude Long-range Observatory (HALO) aircraft. Its small and light design makes it suitable for airborne measurements up to approximately 150 hPa of ambient pressure (13–14 km). The dual laser instrument can measure several trace gases simultaneously in two 36.4-m-path astigmatic Herriott cells with a data acquisition frequency of 1 Hz. We describe the measurement method and the data acquisition of ATTILA and its in-flight performance by focusing on potential sources of influences on the signal, which we investigated with a dedicated test flight during which the instrument sampled from a constant source. We show that linear critical influences associated with challenging movement patterns can be corrected afterwards, while non-linear limitations can be minimized by appropriate calibration frequencies and integrated time intervals. During the recent aircraft campaign CAFE-Brazil (Chemistry of the Atmosphere Field Experiment in Brazil) from December 2022 to January 2023, carbon monoxide (CO) measurements from ATTILA show a good agreement of a R² of 0.89 with simultaneous CO measurements from an established IR spectrometer for airborne measurements, the TRacer In-Situ Tdlas for Atmospheric Research (TRISTAR), on a 10 s time resolution. First dynamical characteristics and tracer distributions of CO and methane (CH₄) over the Amazon rainforest can be identified with ATTILA measurements with a total measurement uncertainty of 10.1 % and 17.5 % and a data accuracy of 0.3 % and 5.5 % for a data acquisition frequency of 1 Hz for CO and CH₄, respectively.

Here, we report the development of a new Quantum cascade Laser infrared Absorption Spectroscopy (QLAS) instrument, the Airborne Tropospheric Tracer In-situ Laser Absorption spectrometer (ATTILA), for atmospheric trace gas measurements on board of the German High-Altitude Long-range Observatory (HALO) aircraft. Its small and light design makes it suitable for airborne measurements up to approximately 150 hPa of ambient pressure (13–14 km). The dual laser instrument can measure several trace gases simultaneously in two 36.4-m-path astigmatic Herriott cells with a data acquisition frequency of 1 Hz. We describe the measurement method and the data acquisition of ATTILA and its in-flight performance by focusing on potential sources of influences on the signal, which we investigated with a dedicated test flight during which the instrument sampled from a constant source. We show that linear critical influences associated with challenging movement patterns can be corrected afterwards, while non-linear limitations can be minimized by appropriate calibration frequencies and integrated time intervals. During the recent aircraft campaign CAFE-Brazil (Chemistry of the Atmosphere Field Experiment in Brazil) from December 2022 to January 2023, carbon monoxide (CO) measurements from ATTILA show a good agreement of a R² of 0.89 with simultaneous CO measurements from an established IR spectrometer for airborne measurements, the TRacer In-Situ Tdlas for Atmospheric Research (TRISTAR), on a 10 s time resolution. First dynamical characteristics and tracer distributions of CO and methane (CH₄) over the Amazon rainforest can be identified with ATTILA measurements with a total measurement uncertainty of 10.1 % and 17.5 % and a data accuracy of 0.3 % and 5.5 % for a data acquisition frequency of 1 Hz for CO and CH₄, respectively.