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In-situ measurements of small atmospheric ice crystals (< 100 µm) on the Antarctic plateau are rare. Yet, small ice crystals are abundant in a region that often reaches cirrus temperatures even in the warmest season. The Particle Phase Discriminator (PPD-2K) was deployed on DOME-C, Antarctica during austral summer 2023/2024. It was used to characterize the microphysical and optical properties of individual ice fog and diamond dust ice crystals having spherical equivalent diameters between 11 and 150 µm. These properties included particle concentration, size distribution and spatial light scattering patterns in the forward direction that allow the analysis of the particle sphericity (particle phase), shape and crystal complexity.

Data of the AquaVIT-4 intercomparison of atmospheric hygrometers which was conducted at the AIDA climate simulation chamber of the Karlsruhe Institute of Technology (KIT), Germany, in March–April 2022, within the framework of the HEMERA H2020 EU project. The objectives were to document the performance of existing hygrometers and to support the development of novel methods for water vapor (H2O) measurements in the upper atmosphere. The AquaVIT-4 intercomparison involved seven hygrometers, based on either infrared laser absorption spectroscopy or frostpoint hygrometry techniques: four deployed on aircraft or stratospheric balloon platforms, and three reference instruments. The simulated conditions in the AIDA chamber reproduced the characteristic atmospheric conditions of the upper troposphere-lower stratosphere (UTLS, altitude range ~5–28 km) in the tropics and mid-latitudes, spanning between 20–600 hPa pressure, 190–245 K temperature, and 0.5–530 ppm H2O mixing ratio. The campaign was divided into two phases, each consisting of four measurement days: an “open intercomparison”, where the simulated conditions were known to the participants, and a “blind intercomparison”, where the conditions were coordinated by independent referees and unknown to the participating teams. Here we present a statistical analysis of the entire dataset, which allows to assess the accuracy and limitations of each instrument. For the accuracy evaluation, two sets of reference measurements were defined: one for in situ instruments, located inside the AIDA vessel, and one for extractive instruments, sampling the chamber gas through a heated inlet. This distinction accounts for H2O desorption effects, which are most prominent at low pressures and low H2O concentrations. All instruments showed a good agreement with the reference values in the range of H2O > 2 ppm, with mean deviations within ±7 % for H2O > 10 ppm, and ±8 % between 2–10 ppm H2O. The largest differences were found for H2O < 2 ppm, a rarely observed range in the atmosphere, though most of the instruments still achieved average deviations within ±10 %. Overall, the results of AquaVIT-4 demonstrate the high accuracy and reliability of the four involved sensors for upper atmospheric monitoring and research applications.

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Data for a study in which we present real-time measurements of organic aerosol (OA) and biogenic volatile organic compounds (BVOCs) at a pine forest stressed by bark beetles and previous droughts close to a biogas power plant (BPP) in western Germany during June 2020. A proton-transfer-reaction time-of-flight mass spectrometer coupled with a particle inlet (CHARON-PTR-ToF-MS) and a Vocus-PTR-ToF-MS were deployed to measure OA and BVOCs. During the entire measurement period, the average concentration of monoterpenes (2.5 ± 5.3 ppb) was higher than isoprene (0.58 ± 0.54 ppb) and sesquiterpenes (0.01 ± 0.01 ppb). The OA composition mainly consisted of semi-volatile organic compounds formed from monoterpene oxidation. Based on a wind direction analysis, BVOC data were categorized into two groups with main influence from the BPP (WD-BPP) and the forest (WD-forest), respectively. In the WD-BPP group, high concentrations of monoterpenes and sesquiterpenes were attributed to BPP emissions. In the WD-forest group, higher temperatures enhanced the biogenic emissions of isoprene, monoterpenes, and sesquiterpenes especially during daytime, exceeding their photochemical consumption. Positive matrix factorization analysis of VOCs revealed substantial contributions of gaseous organic acids from BVOC oxidation during daytime, while weakly oxidized monoterpene products dominated during nighttime. Moreover, increasing relative humidity promoted the gas-to-particle partitioning of gaseous weakly oxidized monoterpene products, leading to an increase of nighttime OA mass. This study highlights that the variations of BVOCs and their oxidation products are influenced by meteorology, local BPP emissions, and chemical transformation processes at this stressed forest.

The provided dataset includes all relevant data to comprehend and reproduce the PhD work of Tobias Schorr with the title "Assessing the Potential of Cirrus Cloud Thinning through Cloud Chamber Experiments and Parcel Model Simulations" (DOI: 10.5445/IR/1000168905).The AIDA cloud chamber data contains a unique experimental investigation of the competition between homogeneous and heterogeneous freezing at cirrus conditions (< 230 K).The climate engineering concept of "cirrus cloud thinning" (CCT) is modeled with the box model MAID and the initialization files as well as result summary tables are provided within the dataset.

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Brown carbon aerosol (BrC) is one major contributor to atmospheric air pollution in Europe, especially in winter. Therefore, we studied the chemical composition, diurnal variation, and sources of BrC from 17th February to 16th March at a rural location in southwest Germany. In total, 178 potential BrC molecules (including 7 nitro aromatic compounds, NACs) were identified in the particle phase comprising on average 63 ± 32 ng m−3, and 31 potential BrC (including 4 NACs) molecules were identified in the gas phase contributing on average 6.2 ± 5.0 ng m−3 during the whole campaign. The 178 potential BrC molecules only accounted for 2.3 ± 1.5 % of the total organic mass, but can explain 11 ± 11 % of the total BrC absorption at 370 nm, assuming an average mass absorption coefficient at 370 nm (MAC370) of 9.5 m2 g−1. A few BrC molecules dominated the total BrC absorption. In addition, diurnal variations show that gas phase BrC was higher at daytime and lower at night. It was mainly controlled by secondary formation (e.g. photooxidation) and particle-to-gas partitioning. Correspondingly, the particle phase BrC was lower at daytime and higher at nighttime. Secondary formation dominates the particle-phase BrC with 61 ± 21 %, while 39 ± 21 % originated from biomass burning. Furthermore, the particle-phase BrC showed decreasing light absorption due to photochemical aging. This study extends the current understanding of real-time behaviors of brown carbon aerosol in the gas and particle phase at a location characteristic for the central Europe.

In-situ measurements of small atmospheric ice crystals (< 100 µm) on the Antarctic plateau are rare. Yet, small ice crystals are abundant in a region that often reaches cirrus temperatures even in the warmest season. The Particle Phase Discriminator (PPD-2K) was deployed on DOME-C, Antarctica during austral summer 2023/2024. It was used to characterize the microphysical and optical properties of individual ice fog and diamond dust ice crystals having spherical equivalent diameters between 11 and 150 µm. These properties included particle concentration, size distribution and spatial light scattering patterns in the forward direction that allow the analysis of the particle sphericity (particle phase), shape and crystal complexity.

The spatiotemporal distribution of aerosol particles in the atmosphere has a great impact on radiative transfer, clouds, and air quality. Modern remote sensing methods, as well as airborne in situ measure- ments by unpiloted aerial vehicles (UAV) or balloons, are suitable tools to improve our understanding of the role of aerosol particles in the atmosphere. To validate the measurement capabilities of three relatively new measurement systems and to bridge the gaps that are often encountered between remote sensing and in situ ob- servation, as well as to investigate aerosol particles in and above the boundary layer, we conducted two measure- ment campaigns and collected a comprehensive dataset employing a scanning aerosol lidar, a balloon-borne ra- diosonde with the Compact Optical Backscatter Aerosol Detector (COBALD), an optical particle counter (OPC) on a UAV, and a comprehensive set of ground-based instruments. The extinction coefficients calculated from near-ground-level aerosol size distributions measured in situ are well correlated with those retrieved from lidar measurements, with a slope of 1.037 ± 0.015 and a Pearson correlation coefficient of 0.878, respectively. Verti- cal profiles measured by an OPC-N3 on a UAV show similar vertical particle distributions and boundary layer heights to lidar measurements. However, the sensor, OPC-N3, shows a larger variability in the aerosol backscat- ter coefficient measurements, with a Pearson correlation coefficient of only 0.241. In contrast, the COBALD data from a balloon flight are well correlated with lidar-derived backscatter data from the near-ground level up to the stratosphere, with a slope of 1.063 ± 0.016 and a Pearson correlation coefficient of 0.925, respectively. This consistency between lidar and COBALD data reflects the good data quality of both methods and proves that lidar can provide reliable and spatial distributions of aerosol particles with high spatial and temporal resolutions. This study shows that the scanning lidar has the capability to retrieve backscatter coefficients near the ground level (from 25 to 50 m above ground level) when it conducts horizontal measurement, which is not possible for verti- cally pointing lidar. These near-ground-level retrievals compare well with ground-level in situ measurements. In addition, in situ measurements on the balloon and UAV validated the scanning lidar retrievals within and above the boundary layer. The scanning aerosol lidar allows us to measure aerosol particle distributions and profiles from the ground level to the stratosphere with an accuracy equal to or better than in situ measurements and with a similar spatial resolution.