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- ItemCharacterization of organic aerosol across the global remote troposphere: A comparison of ATom measurements and global chemistry models(Katlenburg-Lindau : EGU, 2020) Hodzic, Alma; Campuzano-Jost, Pedro; Bian, Huisheng; Chin, Mian; Colarco, Peter R.; Day, Douglas A.; Froyd, Karl D.; Heinold, Bernd; Katich, Joseph M.; Jo, Duseong S.; Kodros, John K.; Nault, Benjamin A.; Pierce, Jeffrey R.; Ray, Eric; Schacht, Jacob; Schill, Gregory P.; Schroder, Jason C.; Schwarz, Joshua P.; Sueper, Donna T.; Tegen, Ina; Tilmes, Simone; Tsigaridis, Kostas; Yu, Pengfei; Jimenez, Jose L.The spatial distribution and properties of submicron organic aerosol (OA) are among the key sources of uncertainty in our understanding of aerosol effects on climate. Uncertainties are particularly large over remote regions of the free troposphere and Southern Ocean, where very few data have been available and where OA predictions from AeroCom Phase II global models span 2 to 3 orders of magnitude, greatly exceeding the model spread over source regions. The (nearly) pole-to-pole vertical distribution of nonrefractory aerosols was measured with an aerosol mass spectrometer onboard the NASA DC-8 aircraft as part of the Atmospheric Tomography (ATom) mission during the Northern Hemisphere summer (August 2016) and winter (February 2017). This study presents the first extensive characterization of OA mass concentrations and their level of oxidation in the remote atmosphere. OA and sulfate are the major contributors by mass to submicron aerosols in the remote troposphere, together with sea salt in the marine boundary layer. Sulfate was dominant in the lower stratosphere. OA concentrations have a strong seasonal and zonal variability, with the highest levels measured in the lower troposphere in the summer and over the regions influenced by biomass burning from Africa (up to 10 μgsm-3). Lower concentrations (~ 0:1 0.3 μgsm-3) are observed in the northern middle and high latitudes and very low concentrations (< 0:1 μgsm-3) in the southern middle and high latitudes. The ATom dataset is used to evaluate predictions of eight current global chemistry models that implement a variety of commonly used representations of OA sources and chemistry, as well as of the AeroCom-II ensemble. The current model ensemble captures the average vertical and spatial distribution of measured OA concentrations, and the spread of the individual models remains within a factor of 5. These results are significantly improved over the AeroCom-II model ensemble, which shows large overestimations over these regions. However, some of the improved agreement with observations occurs for the wrong reasons, as models have the tendency to greatly overestimate the primary OA fraction and underestimate the sec-ondary fraction. Measured OA in the remote free troposphere is highly oxygenated, with organic aerosol to organic carbon (OA= OC) ratios of ~ 2.2 2.8, and is 30 % 60% more oxygenated than in current models, which can lead to significant errors in OA concentrations. The model measurement comparisons presented here support the concept of a more dynamic OA system as proposed by Hodzic et al. (2016), with enhanced removal of primary OA and a stronger production of secondary OA in global models needed to provide better agreement with observations. © 2020 IEEE Computer Society. All rights reserved.
- ItemShip-based measurements of ice nuclei concentrations over the Arctic, Atlantic, Pacific and Southern oceans(Katlenburg-Lindau : EGU, 2020) Welti, André; Bigg, Keith E.; DeMott, Paul J.; Gong, Xianda; Hartmann, Markus; Harvey, Mike; Henning, Silvia; Herenz, Paul; Hill, Thomas C.J.; Hornblow, Blake; Leck, Caroline; Löffler, Mareike; McCluskey, Christina S.; Rauker, Anne Marie; Schmale, Julia; Tatzelt, Christian; van Pinxteren, Manuela; Stratmann, FrankAmbient concentrations of ice-forming particles measured during ship expeditions are collected and summarised with the aim of determining the spatial distribution and variability in ice nuclei in oceanic regions. The presented data from literature and previously unpublished data from over 23 months of ship-based measurements stretch from the Arctic to the Southern Ocean and include a circumnavigation of Antarctica. In comparison to continental observations, ship-based measurements of ambient ice nuclei show 1 to 2 orders of magnitude lower mean concentrations. To quantify the geographical variability in oceanic areas, the concentration range of potential ice nuclei in different climate zones is analysed by meridionally dividing the expedition tracks into tropical, temperate and polar climate zones. We find that concentrations of ice nuclei in these meridional zones follow temperature spectra with similar slopes but vary in absolute concentration. Typically, the frequency with which specific concentrations of ice nuclei are observed at a certain temperature follows a log-normal distribution. A consequence of the log-normal distribution is that the mean concentration is higher than the most frequently measured concentration. Finally, the potential contribution of ship exhaust to the measured ice nuclei concentration on board research vessels is analysed as function of temperature. We find a sharp onset of the influence at approximately 36 C but none at warmer temperatures that could bias ship-based measurements. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemThree-dimensional evolution of Saharan dust transport towards Europe based on a 9-year EARLINET-optimized CALIPSO dataset(Katlenburg-Lindau : EGU, 2017) Marinou, Eleni; Amiridis, Vassilis; Binietoglou, Ioannis; Tsikerdekis, Athanasios; Solomos, Stavros; Proestakis, Emannouil; Konsta, Dimitra; Papagiannopoulos, Nikolaos; Tsekeri, Alexandra; Vlastou, Georgia; Zanis, Prodromos; Balis, Dimitrios; Wandinger, Ulla; Ansmann, AlbertIn this study we use a new dust product developed using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) observations and EARLINET (European Aerosol Research Lidar Network) measurements and methods to provide a 3-D multiyear analysis on the evolution of Saharan dust over North Africa and Europe. The product uses a CALIPSO L2 backscatter product corrected with a depolarization-based method to separate pure dust in external aerosol mixtures and a Saharan dust lidar ratio (LR) based on long-term EARLINET measurements to calculate the dust extinction profiles. The methodology is applied on a 9-year CALIPSO dataset (2007-2015) and the results are analyzed here to reveal for the first time the 3-D dust evolution and the seasonal patterns of dust over its transportation paths from the Sahara towards the Mediterranean and Continental Europe. During spring, the spatial distribution of dust shows a uniform pattern over the Sahara desert. The dust transport over the Mediterranean Sea results in mean dust optical depth (DOD) values up to 0.1. During summer, the dust activity is mostly shifted to the western part of the desert where mean DOD near the source is up to 0.6. Elevated dust plumes with mean extinction values between 10 and 75 Mm-1 are observed throughout the year at various heights between 2 and 6 km, extending up to latitudes of 40° N. Dust advection is identified even at latitudes of about 60° N, but this is due to rare events of episodic nature. Dust plumes of high DOD are also observed above the Balkans during the winter period and above northwest Europe during autumn at heights between 2 and 4 km, reaching mean extinction values up to 50 Mm-1. The dataset is considered unique with respect to its potential applications, including the evaluation of dust transport models and the estimation of cloud condensation nuclei (CCN) and ice nuclei (IN) concentration profiles. Finally, the product can be used to study dust dynamics during transportation, since it is capable of revealing even fine dynamical features such as the particle uplifting and deposition on European mountainous ridges such as the Alps and Carpathian Mountains.
- ItemMolecular distributions of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls in PM2.5 collected at the top of Mt. Tai, North China, during the wheat burning season of 2014(Katlenburg-Lindau : EGU, 2018) Zhu, Yanhong; Yang, Lingxiao; Chen, Jianmin; Kawamura, Kimitaka; Sato, Mamiko; Tilgner, Andreas; van Pinxteren, Dominik; Chen, Ying; Xue, Likun; Wang, Xinfeng; Simpson, Isobel J.; Herrmann, Hartmut; Blake, Donald R.; Wang, WenxingFine particulate matter (PM2.5) samples collected at Mount (Mt.) Tai in the North China Plain during summer 2014 were analyzed for dicarboxylic acids and related compounds (oxocarboxylic acids and α-dicarbonyls) (DCRCs). The total concentration of DCRCs was 1050±580 and 1040±490ng m-3 during the day and night, respectively. Although these concentrations were about 2 times lower than similar measurements in 2006, the concentrations reported here were about 1-13 times higher than previous measurements in other major cities in the world. Molecular distributions of DCRCs revealed that oxalic acid (C2) was the dominant species (50%), followed by succinic acid (C4) (12%) and malonic acid (C3) (8%). WRF modeling revealed that Mt. Tai was mostly in the free troposphere during the campaign and long-range transport was a major factor governing the distributions of the measured compounds at Mt. Tai. A majority of the samples (79%) had comparable concentrations during the day and night, with their day-night concentration ratios between 0.9 and 1.1. Multi-day transport was considered an important reason for the similar concentrations. Correlation analyses of DCRCs and their gas precursors and between C2 and sulfate indicated precursor emissions and aqueous-phase oxidations during long-range transport also likely play an important role, especially during the night. Source identification indicated that anthropogenic activities followed by photochemical aging accounted for about 60% of the total variance and were the dominant source at Mt. Tai. However, biomass burning was only important during the first half of the measurement period. Measurements of potassium (K+) and DCRCs were about 2 times higher than those from the second half of the measurement period. The concentration of levoglucosan, a biomass burning tracer, decreased by about 80% between 2006 and 2014, indicating that biomass burning may have decreased between 2006 and 2014.
- ItemNorth African mineral dust sources: New insights from a combined analysis based on 3D dust aerosol distributions, surface winds and ancillary soil parameters(Katlenburg-Lindau : EGU, 2020) Vandenbussche, Sophie; Callewaert, Sieglinde; Schepanski, Kerstin; De Mazière, MartineMineral dust aerosol is a key player in the climate system. Determining dust sources and the spatio-temporal variability of dust emission fluxes is essential for estimating the impact of dust on the atmospheric radiation budget, cloud and precipitation formation processes, the bio-productivity and, ultimately, the carbon cycle. Although much effort has been put into determining dust sources from satellite observations, geo-locating active dust sources is still challenging and uncertainties in space and time are evident. One major source of uncertainty is the lack of clear differentiation between near-source dust aerosol and transported dust aerosol. In order to reduce this uncertainty, we use 3D information on the distribution of dust aerosol suspended in the atmosphere calculated from spectral measurements obtained by the Infrared Atmospheric Sounding Interferometer (IASI) by using the Mineral Aerosols Profiling from Infrared Radiance (MAPIR) algorithm. In addition to standard dust products from satellite observations, which provide 2D information on the horizontal distribution of dust, MAPIR allows for the retrieval of additional information on the vertical distribution of dust plumes. This ultimately enables us to separate between near-source and transported dust plumes. Combined with information on near-surface wind speed and surface properties, low-altitude dust plumes can be assigned to dust emission events and low-altitude transport regimes can be excluded. Consequently, this technique will reduce the uncertainty in automatically geo-locating active dust sources. The findings of our study illustrate the spatio-temporal distribution of North African dust sources based on 9 years of data, allowing for the observation of a full seasonal cycle of dust emissions, differentiating morning and afternoon/evening emissions and providing a first glance at long-term changes. In addition, we compare the results of this new method to the results from Schepanski et al. (2012), who manually identified dust sources from Spinning Enhanced Visible and InfraRed Imager (SEVIRI) red-green-blue (RGB) images. The comparison illustrates that each method has its strengths and weaknesses that must be taken into account when using the results. This study is of particular importance for understanding future environmental changes due to a changing climate. © Author(s) 2020