Johannes Heuser

The current observational coverage of the atmospheric boundary layer (ABL) remains insufficient to improve high-resolution forecasting, including numerical weather prediction (NWP) and nowcasting, particularly for severe weather events. The existing measurement networks cannot provide, at sufficient spatial and temporal resolution, the vertically resolved kinematic and thermodynamic information needed to resolve the ABL for high-resolution forecasting. In order to address this shortcoming, the German Weather Service, Deutscher Wetterdienst (DWD), is currently expanding its operational network to include ground-based vertical profile measurements. Lidar remote sensing profilers are being installed at thirteen selected weather stations across Germany. These stations will complement DWD’s observation systems, such as radiosondes, radar wind profilers, and AMDAR measurements.Doppler-lidar systems and differential absorption lidars (DIALs) will allow for the continuous retrieval of wind and humidity across the boundary layer. The DIALs, DA10 atmospheric profilers by Vaisala, will be used to provide vertical humidity profiles up to 4 km above ground level based on broadband differential absorption at two wavelengths in the near-infrared spectrum.As part of their deployment, the DA10 units undergo extensive characterisation and testing. This includes continuous monitoring of the technical parameters alongside the measured water vapour mixing ratio and attenuated backscatter profiles, enabling the simultaneous assessment of operational reliability and data quality across a wide range of meteorological conditions. In conjunction with this monitoring, systematic intercomparisons were conducted both among the DA10 units themselves and against established reference measurements, primarily radiosondes, further strengthening this assessment. Initial results indicate a good overall agreement between the DIALs’ humidity profiles and the radiosonde measurements, while also highlighting the limitations of these commercially available lidars for systematic measurements of ground-based humidity profiles.

Improving convective-scale forecasts requires more detailed and continuous observational data of thermodynamic profiles and wind profiles in the atmospheric boundary layer (ABL) than currently available. To meet these data requirements, DWD is establishing a network of various surface remote sensing systems targeted on ABL-profiling for routine network operation. This involves integrating 13 Doppler lidars for observing wind profiles and 13 broadband differential absorption lidars (DIALs) for observing water vapor profiles into the network at selected surface stations across Germany until end of 2027.This contribution reports the results from the assessment of the DIAL, the DA10 from Vaisala, for water vapor profiling network performance and its ability to improve the boundary-layer moisture in a limited-area numerical weather prediction system. The Vaisala DA10 instrument is designed to provide operational water vapor profile observations in the ABL, without the need for calibration. We operate two DA10 units at the Observatory Lindenberg to evaluate all aspects of instrument reliability, operational sustainability, data quality, and on the potential benefit for the NWP using assimilation experiments. Our methods include comparisons with radiosounding observations (4 per day) over at least one year of continuous observations, as well as observation-minus-background statistics between the DA10s and the regional model system ICON-D2 to identify observation errors and to evaluate the model performance with respect to boundary-layer moisture, e.g., under convection. Furthermore, we present first results from assimilating the DA10 water vapor profiles into the kilometer-scale ensemble data assimilation system (KENDA).Summarizing, this presentation provides an overview of the DA10 network's operational viability for monitoring water vapour profiles 24/7 and for providing additional information for convective-scale data assimilation.

Les particules carbonées de suies sont formées pendant la combustion incomplète de combustibles fossiles, biocarburants et biomasse et sont considérées comme contribuant à une partie importante des émissions d’aérosols, en particulier dans les zones polluées. Il est connu que les particules de suie contiennent des fractions de carbone absorbant, telles que le carbone noir (BC) et le carbone brun (BrC), ce qui en fait une espèce clef pour comprendre et estimer l’interaction entre les aérosols et le rayonnement atmosphérique, i.e. l’effet radiatif direct (DRE). Les estimations actuelles du DRE des suies et de ses composantes BC et BrC restent incertaines à cause de la difficulté à représenter leurs propriétés microphysiques et optiques spectrales dans des modèles. En particulier, des lacunes persistent dans la description de la variabilité des propriétés optiques des suies à l’émission, à cause des différentes conditions de combustion, et de leurs changements au cours du temps de vie dans l’atmosphère, lors du mélange avec d’autres aérosols. De plus, des différences entre les observations réalisées en laboratoire et les mesures sur le terrain demeurent et ne sont pas comprises.Ces travaux de thèse visent à fournir de nouvelles mesures et descriptions des propriétés physiques, chimiques et optiques des suies et de leur fraction BC et BrC afin d’améliorer leur représentation dans les modèles. L’objectif est donc de faire progresser la compréhension et la description de la variabilité des propriétés des suies 1) lors de l’émission, pour des conditions de combustion variables, et 2) pendant le vieillissement dans l’atmosphère, en particulier, à cause du mélange interne avec des composés organiques et inorganiques formant un revêtement à la surface des suies. Afin de réaliser une étude mécanistique des propriétés des suies, un ensemble cohérent d’expériences a été mis en place en utilisant la chambre de simulation atmosphérique CESAM (Chambre Expérimentale de Simulation Atmosphérique Multiphasique) et un générateur de suies à base de propane. Les expériences ont été déployées afin de déterminer des paramètres optiques clef, utilisés en modélisation et télédétection, comme les sections efficaces d’absorption, extinction, et diffusion (MAC, MEC, MSC), l’albédo de simple diffusion (SSA), et l’indice de réfraction complexe (CRI). Les propriétés des suies issues de différentes conditions de combustion ont permis d’établir une relation généralisée entre le MAC et la composition chimique des particules fraîchement émises. Des calculs optiques basés sur deux descriptions de la morphologie des particules ont été effectués pour déterminer le CRI des suies et discuter de l’utilisabilité et de la pertinence des données pour des différentes hypothèses de représentations de la forme.Les aérosols de suie ont été soumis à différents processus de vieillissement atmosphérique simulés afin de déterminer les effets du vieillissement sur leur capacité d'absorption et leurs propriétés physico-chimiques. En particulier, la formation d'un revêtement et l'augmentation de l'absorption due à ce mélange interne ont été étudiées pour deux précurseurs et processus de revêtement. Cela a permis d'étudier la relation entre l'augmentation de l'absorption, le vieillissement des particules et l'épaisseur du revêtement, d’intérêt tout au long du cycle de vie des suies.

Black carbon (BC) soot aerosol, produced during the incomplete combustion of fossil fuels, biofuels, and biomasses, is a major light-absorbing species and a key climate forcer. Despite its importance, BC remains challenging to represent in models due to persistent uncertainties in its spectral optical properties. In particular, the formation of non-absorbing coatings on fractal BC soot is a ubiquitous atmospheric process that enhances absorption, yet the magnitude of this enhancement (Eabs) remains highly uncertain and poorly represented in current models.In order to advance on this topic, a set of experiments were performed using the 4.2 m3 CESAM simulation chamber on BC-soot aerosol generated from a propane diffusion flame. Experiments were conceived to systematically investigate the impact of coating formation and further ageing on soot spectral optical properties. Two chemical systems inducing the formation of a coating by a second scattering aerosol phase produced via the photo-oxidation of SO2 and the ozonolysis of α-pinene were considered.The resulting dataset quantifies the magnitude and variability of Eabs under varying conditions, highlighting its dependence on soot morphology, soot–coating structure, and particle-to-particle heterogeneous mixing state. We show that the relative importance of these factors evolves with the dynamics of coating formation and ageing. Importantly, the Eabs cannot be reliably predicted using a fixed value or simple core–shell optical models, as commonly assumed in climate simulations.

The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, several aspects influencing the variability of C, particularly those related to aerosol microphysical properties, are still not fully constrained. In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments. The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 ± 0.03 to 3.9 ± 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm⁻¹. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 200 nm. This size dependence is relatively small (within 25 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles. These results are relevant for improving the accuracy and comparability of aerosol absorption measurements performed by aethalometers, particularly within monitoring networks. The observed dependence of C on particle size suggests that differences between urban and remote sites, or between periods dominated by nucleation versus coarse-mode particles (e.g., dust), may contribute to the variability reported across locations. Understanding these dependencies is essential for refining correction approaches and reducing inter-site discrepancies in network datasets.

The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, the factors influencing variability of C remain poorly understood, particularly in relation to aerosol properties. In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments. The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 ± 0.03 to 3.9 ± 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm⁻¹. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 120 nm. This size dependence is relatively small (within 15 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles.

The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, the factors influencing variability of C remain poorly understood, particularly in relation to aerosol properties. In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments. The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 ± 0.03 to 3.9 ± 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm⁻¹. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 120 nm. This size dependence is relatively small (within 15 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles.

The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, the factors influencing variability of C remain poorly understood, particularly in relation to aerosol properties. In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments. The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 ± 0.03 to 3.9 ± 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm⁻¹. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 120 nm. This size dependence is relatively small (within 15 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles.

The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, the factors influencing variability of C remain poorly understood, particularly in relation to aerosol properties. In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments. The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 ± 0.03 to 3.9 ± 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm⁻¹. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 120 nm. This size dependence is relatively small (within 15 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles.

The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, the factors influencing variability of C remain poorly understood, particularly in relation to aerosol properties. In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments. The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 ± 0.03 to 3.9 ± 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm⁻¹. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 120 nm. This size dependence is relatively small (within 15 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles.