Aerosol particles acting as cloud condensation nuclei (CCN) or ice-nucleating particles (INPs) play a major role in the formation and glaciation of clouds. Thereby they exert a strong impact on the ...radiation budget of the Earth. Data on abundance and properties of both types of particles are sparse, especially for remote areas of the world, such as the Southern Ocean (SO). In this work, we present unique results from ship-borne aerosol-particle-related in situ measurements and filter sampling in the SO region, carried out during the Antarctic Circumnavigation Expedition (ACE) in the austral summer of 2016–2017. An overview of CCN and INP concentrations over the Southern Ocean is provided and, using additional quantities, insights regarding possible CCN and INP sources and origins are presented.
CCN number concentrations spanned 2 orders of magnitude, e.g. for a supersaturation of 0.3 % values ranged roughly from 3 to 590 cm−3.
CCN showed variable contributions of organic and inorganic material (inter-quartile range of hygroscopicity parameter κ from 0.2 to 0.9).
No distinct size dependence of κ was apparent, indicating homogeneous composition across sizes (critical dry diameter on average between 30 and 110 nm).
The contribution of sea spray aerosol (SSA) to the CCN number concentration was on average small.
Ambient INP number concentrations were measured in the temperature range from −5 to −27 ∘C using an immersion freezing method. Concentrations spanned up to 3 orders of magnitude, e.g. at −16 ∘C from 0.2 to 100 m−3.
Elevated values (above 10 m−3 at −16 ∘C) were measured when the research vessel was in the vicinity of land (excluding Antarctica), with lower and more constant concentrations when at sea. This, along with results of backward-trajectory analyses, hints towards terrestrial and/or coastal INP sources being dominant close to ice-free (non-Antarctic) land.
In pristine marine areas INPs may originate from both oceanic sources and/or long-range transport.
Sampled aerosol particles (PM10) were analysed for sodium and methanesulfonic acid (MSA). Resulting mass concentrations were used as tracers for primary marine and secondary aerosol particles, respectively.
Sodium, with an average mass concentration around 2.8 µg m−3, was found to dominate the sampled, identified particle mass.
MSA was highly variable over the SO, with mass concentrations up to 0.5 µg m−3 near the sea ice edge.
A correlation analysis yielded strong correlations between sodium mass concentration and particle number concentration in the coarse mode, unsurprisingly indicating a significant contribution of SSA to that mode.
CCN number concentration was highly correlated with the number concentration of Aitken and accumulation mode particles. This, together with a lack of correlation between sodium mass and Aitken and accumulation mode number concentrations, underlines the important contribution of non-SSA, probably secondarily formed particles, to the CCN population. INP number concentrations did not significantly correlate with any other measured aerosol physico-chemical parameter.
Aerosol measurements over the Southern Ocean are used to constrain
aerosol–cloud interaction radiative forcing (RFaci) uncertainty in a global climate model. Forcing uncertainty is quantified using 1 ...million climate model variants that sample the uncertainty in nearly 30 model parameters. Measurements of cloud condensation nuclei and other aerosol properties from an Antarctic circumnavigation expedition strongly constrain natural aerosol emissions: default sea spray emissions need to be increased by around a factor of 3 to be consistent with measurements. Forcing uncertainty is reduced by around 7 % using this set of several hundred measurements, which is comparable to the 8 % reduction achieved using a diverse and extensive set of over 9000 predominantly Northern Hemisphere measurements. When Southern Ocean and Northern Hemisphere measurements are combined, uncertainty in RFaci is reduced by 21 %, and the strongest 20 % of forcing values are ruled out as implausible. In this combined constraint, observationally plausible RFaci is around 0.17 W m−2 weaker (less negative) with 95 % credible values ranging from −2.51 to
−1.17 W m−2 (standard deviation of −2.18 to −1.46 W m−2). The Southern Ocean and Northern Hemisphere measurement datasets are complementary because they constrain different processes. These results
highlight the value of remote marine aerosol measurements.
Ambient 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.
Uncertainty in radiative forcing caused by aerosol–cloud interactions is about twice as large as for CO₂ and remains the least well understood anthropogenic contribution to climate change. A major ...cause of uncertainty is the poorly quantified state of aerosols in the pristine preindustrial atmosphere, which defines the baseline against which anthropogenic effects are calculated. The Southern Ocean is one of the few remaining near-pristine aerosol environments on Earth, but there are very few measurements to help evaluate models. The Antarctic Circumnavigation Expedition: Study of Preindustrial-like Aerosols and their Climate Effects (ACE-SPACE) took place between December 2016 and March 2017 and covered the entire Southern Ocean region (Indian, Pacific, and Atlantic Oceans; length of ship track 33,000 km) including previously unexplored areas. In situ measurements covered aerosol characteristics e.g., chemical composition, size distributions, and cloud condensation nuclei (CCN) number concentrations, trace gases, and meteorological variables. Remote sensing observations of cloud properties, the physical and microbial ocean state, and back trajectory analyses are used to interpret the in situ data. The contribution of sea spray to CCN in the westerly wind belt can be larger than 50%. The abundance of methanesulfonic acid indicates local and regional microbial inf luence on CCN abundance in Antarctic coastal waters and in the open ocean. We use the in situ data to evaluate simulated CCN concentrations from a global aerosol model. The extensive, available ACE-SPACE dataset (https://zenodo.org/communities/spi-ace?page=1&size=20) provides an unprecedented opportunity to evaluate models and to reduce the uncertainty in radiative forcing associated with the natural processes of aerosol emission, formation, transport, and processing occurring over the pristine Southern Ocean.
The Southern Ocean is a critical component of Earth's climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large ...scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, and ocean biogeochemistry and microbiology. This circumpolar cruise included visits to 12 remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter-term variations, geographic setting of environmental processes, and interactions between them over the duration of 90 d. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable we applied an unsupervised machine learning method, the sparse principal component analysis (sPCA), which describes environmental processes through 14 latent variables. To derive a robust statistical perspective on these processes and to estimate the uncertainty in the sPCA decomposition, we have developed a bootstrap approach. Our results provide a proof of concept that sPCA with uncertainty analysis is able to identify temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and “hotspots” of interaction between environmental compartments. While confirming many well known processes, our analysis provides novel insights into the Southern Ocean water cycle (freshwater fluxes), trace gases (interplay between seasonality, sources, and sinks), and microbial communities (nutrient limitation and island mass effects at the largest scale ever reported). More specifically, we identify the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity; the fact that sea ice controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilisation and reduced light limitation; and the clear regional patterns of aerosol characteristics that have emerged, stressing the role of the sea state, atmospheric chemical processing, and source processes near hotspots for the availability of cloud condensation nuclei and hence cloud formation. A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper-ocean layer light intensity, surface wind speed and relative humidity played an important role in our analysis, highlighting the necessity for Earth system models to represent them adequately. In conclusion, our study highlights the use of sPCA to identify key ocean–atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. It thereby fills an important gap between simple correlation analyses and complex Earth system models. The sPCA processing code is available as open-access from the following link: https://renkulab.io/gitlab/ACE-ASAID/spca-decomposition (last access: 29 March 2021). As we show here, it can be used for an exploration of environmental data that is less prone to cognitive biases (and confirmation biases in particular) compared to traditional regression analysis that might be affected by the underlying research question.
The Arctic is sensitive to cloud radiative forcing. Due to the limited number of aerosols present throughout much of the year, cloud formation is susceptible to the presence of cloud condensation ...nuclei and ice nucleating particles (INPs). Primary biological aerosol particles (PBAP) contribute to INPs and can impact cloud phase, lifetime, and radiative properties. We present yearlong observations of hyperfluorescent aerosols (HFA), tracers for PBAP, conducted with a Wideband Integrated Bioaerosol Sensor, New Electronics Option during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition (October 2019–September 2020) in the central Arctic. We investigate the influence of potential anthropogenic and natural sources on the characteristics of the HFA and relate our measurements to INP observations during MOSAiC. Anthropogenic sources influenced HFA during the Arctic haze period. But surprisingly, we also found sporadic “bursts” of HFA with the characteristics of PBAP during this time, albeit with unclear origin. The characteristics of HFA between May and August 2020 and in October 2019 indicate a strong contribution of PBAP to HFA. Notably from May to August, PBAP coincided with the presence of INPs nucleating at elevated temperatures, that is, >−9°C, suggesting that HFA contributed to the “warm INP” concentration. The air mass residence time and area between May and August and in October were dominated by the open ocean and sea ice, pointing toward PBAP sources from within the Arctic Ocean. As the central Arctic changes drastically due to climate warming with expected implications on aerosol–cloud interactions, we recommend targeted observations of PBAP that reveal their nature (e.g., bacteria, diatoms, fungal spores) in the atmosphere and in relevant surface sources, such as the sea ice, snow on sea ice, melt ponds, leads, and open water, to gain further insights into the relevant source processes and how they might change in the future.
Aerosol particles acting as cloud condensation nuclei (CCN) or ice nucleating parti-
cles (INP) play a major role in the formation and glaciation of clouds. Thereby they exert a strong impact on the ...radiation budget of the Earth. Data on abundance and properties of both particle types are sparse, especially for remote areas of the world, such as the Southern Ocean (SO).
In this work, unique results from ship-borne aerosol-particle-related in situ measurements and filter sampling in the summertime SO region are presented. An overview of CCN and INP number concentrations on the Southern Ocean is provided and, using additional analyses on particle chemical composition and air-mass origin, insights regarding possible CCN and INP sources and origins are
presented, with the help of a correlation analysis.
CCN number concentrations spanned 2 orders of magnitude, e.g. for a supersaturation of 0.3 % values ranged roughly from 3 to 590 cm⁻³. CCN showed variable contributions of organic and inorganic material. No distinct size-dependence of the CCN hygroscopicity parameter was apparent, indicating homogeneous composition across sizes (critical dry diameter on average between 30 nm and 110 nm). The relative contribution of sea spray aerosol (SSA) to the CCN number concentration
was on average small (below 35 %).
Ambient INP number concentrations were measured in the temperature range from −4 to −27 °C using an immersion freezing method. Concentrations spanned up to 3 orders of magnitude, e.g. at −16 °C from 0.2 to 100 m⁻³. Elevated values (above 10 m⁻³ at −16 °C) were measured when the research vessel was in the vicinity of land (excluding Antarctica). Lower, more constant concentrations were measured on the open ocean. This, along with results of backward-trajectory analyses, hints towards terrestrial and/or coastal INP sources being dominant close to ice-free (non-Antarctic) land. In pristine marine areas INP may originate from both oceanic sources and/or long range transport.
A correlation analysis yielded strong correlations between sodium mass concentration and particle number concentration in the coarse mode (larger 1 µm), unsurprisingly indicating a significant contribution of SSA to that mode. CCN number concentration was highly correlated with the number concentrations of Aitken (10 to 100 nm) and accumulation mode particles (100 to 1000 nm). This, together with a lack of correlation between sodium mass and Aitken and accumulation mode number concentrations, underlines the important contribution of non-SSA, probably secondarily formed particles, to the CCN population.:1 Introduction
2 Fundamentals
2.1 Aerosol particle activation
2.1.1 Köhler theory
2.1.2 κ-Köhler theory
2.2 Ice nucleation
2.2.1 Homogeneous Freezing
2.2.2 Heterogeneous Freezing
3 Campaign, instrumentation, and data handling
3.1 Antarctic Circum-navigation Expedition
3.2 In situ aerosol measurements
3.2.1 Aerosol number size distribution
3.2.2 Cloud condensation nuclei
3.3 Off-line aerosol characterisation
3.3.1 High-volume sampling
3.3.2 Low-volume sampling
3.3.3 Ice nucleation droplet array (INDA)
3.3.4 Analysis of chemical composition
3.4 Further resources
3.4.1 In-water organic compound measurements
3.4.2 Wind measurements
3.4.3 Air-mass origin analysis
3.4.4 Fluorescent particles
3.4.5 Correlation analysis
4 Results and Discussion
4.1 Aerosol particles and cloud condensation nuclei
4.1.1 Particle number size distributions
4.1.2 CCN number concentrations
4.1.3 CCN hygroscopicity
4.1.4 Air-mass origin for aerosol particle and CCN measurements
4.2 Ice nucleating particles
4.2.1 INP abundance
4.2.2 Air-mass origin for INP measurements
4.3 Chemical composition of sampled aerosol particles
4.4 Correlation analysis
5 Summary and Conclusions
Aerosolpartikel, die als Wolkennukleations- oder Eiskeime fungieren, spielen eine Schlüsselrolle in den Entstehungs- und Vereisungsprozessen von Wolken. Mit ihren wolkenrelevanten Eigenschaften haben diese beiden Arten von Aerosolpartikeln einen starken Einfluss auf den Strahlungshaushalt der Erde. Messungen ihrer Häufigkeit und Eigenschaften sind selten, inbesondere in den entlegenen Regionen der Erde wie beispielsweise dem Südlichen Ozean.
In dieser Arbeit werden die Ergebnisse von in situ und filterbasierten Partikelmessungen einer Forschungsfahrt auf dem Südlichen Ozean in den Sommermonaten der Südhalbkugel gezeigt. Ein erstmaliger Überblick über die Anzahlkonzentrationen der Wolkennukleations- und Eiskeime über dem Südlichen Ozean wird gegeben. Unter Berücksichtigung weiterer Messergebnisse zur chemischen Zusammensetzung der Partikel und Betrachtungen zur Herkunft der Luftmassen werden Rückschlüsse
auf die Herkunft und Quellen der gesammelten, wolkenrelevanten Aerosolpartikel gezogen, auch mit Hilfe einer Korrelationsanalyse.
Die Anzahlkonzentration der Wolkennukleationskeime schwankte innerhalb von zwei Größenordnungen, beispielsweise zwischen 3 und 590 cm⁻³ bei 0.3 % Übersättigung. Die chemische Zusammensetzung der Wolkennukleationskeime variierte dabei stark, zwischen organischem und inorganischem Material. Der Hygroskopizitätsparameter zeigte keine Größenabhängigkeit, was für eine intern gemischte Population von Wolkennukleationskeimen spricht (kritische Partikeldurchmesser lagen im
Mittel zwischen 30 und 110 nm). Der prozentuale Anteil von Seesalzpartikeln zur Anzahlkonzentration der Wolkennukleationskeime war im Mittel gering (kleiner 35 %).
Die Anzahlkonzentration der Eiskeime wurden im Temperaturbereich −4 bis −27 °C mittels einer filterbasierten Immersionsgefriermethode bestimmt. Die Anzahlkonzentrationen schwankten dabei im Bereich von bis zu drei Größenordnungen, beispielsweise zwischen 0.2 und 100 m⁻³ bei einer Temperatur von −16 °C. In Küstennähe, mit Ausnahme von Antarktika, wurden erhöhte Anzahlkonzen-
trationen (über 10 m⁻³ bei −16 °C) gemessen. Niedrigere, weniger variable Anzahlkonzentrationen wurden hingegen auf offener See gemessen. Diese Beobachtungen, zusammen mit den Ergebnissen zur Luftmassenherkunft, sprechen für eine Dominanz von terrestrischen und/oder küstennahen Quellen der Eiskeime in der Nähe von eisfreiem (nicht-Antarktischem) Festland. Dabei können in den unbe-
rührten, marinen Regionen die Eiskeime aus dem Meer selbst und/oder Ferntransport stammen.
Eine Korrelationsanalyse zeigte einen starken Zusammenhang zwischen der Massenkonzentration von Natrium und der Anzahlkonzentration an groben Aerosolpartikeln (größer 1 µm). Daraus folgt ein signifikanter Anteil an Seesalzpartikeln in dieser Partikelgröße. Die Anzahlkonzentration der Wolkennukleationskeime korrelierte stark mit den Anzahlkonzentrationen der Aitken- (10 bis 100 nm) bzw. Akkumulationskerne (100 bis 1000 nm). Diese Beobachtung, zusammen mit dem Fehlen einer Korrelation zwischen Natriummasse und Aitken- oder Akkumulationskernanzahl, unterstreicht die Relevanz von Partikeln die nicht Seesalz sind (vermutlich sekundär geformten Aerosolpartikel) für die Population der Wolkennukleationskeime.:1 Introduction
2 Fundamentals
2.1 Aerosol particle activation
2.1.1 Köhler theory
2.1.2 κ-Köhler theory
2.2 Ice nucleation
2.2.1 Homogeneous Freezing
2.2.2 Heterogeneous Freezing
3 Campaign, instrumentation, and data handling
3.1 Antarctic Circum-navigation Expedition
3.2 In situ aerosol measurements
3.2.1 Aerosol number size distribution
3.2.2 Cloud condensation nuclei
3.3 Off-line aerosol characterisation
3.3.1 High-volume sampling
3.3.2 Low-volume sampling
3.3.3 Ice nucleation droplet array (INDA)
3.3.4 Analysis of chemical composition
3.4 Further resources
3.4.1 In-water organic compound measurements
3.4.2 Wind measurements
3.4.3 Air-mass origin analysis
3.4.4 Fluorescent particles
3.4.5 Correlation analysis
4 Results and Discussion
4.1 Aerosol particles and cloud condensation nuclei
4.1.1 Particle number size distributions
4.1.2 CCN number concentrations
4.1.3 CCN hygroscopicity
4.1.4 Air-mass origin for aerosol particle and CCN measurements
4.2 Ice nucleating particles
4.2.1 INP abundance
4.2.2 Air-mass origin for INP measurements
4.3 Chemical composition of sampled aerosol particles
4.4 Correlation analysis
5 Summary and Conclusions
The etiologies of neurodegenerative diseases may be diverse; however, a common pathological denominator is the formation of aberrant protein conformers and the occurrence of pathognomonic ...proteinaceous deposits. Different approaches coming from neuropathology, genetics, animal modeling and biophysics have established a crucial role of protein misfolding in the pathogenic process. However, there is an ongoing debate about the nature of the harmful proteinaceous species and how toxic conformers selectively damage neuronal populations. Increasing evidence indicates that soluble oligomers are associated with early pathological alterations, and strikingly, oligomeric assemblies of different disease‐associated proteins may share common structural features. A major step towards the understanding of mechanisms implicated in neuronal degeneration is the identification of genes, which are responsible for familial variants of neurodegenerative diseases. Studies based on these disease‐associated genes illuminated the two faces of protein misfolding in neurodegeneration: a gain of toxic function and a loss of physiological function, which can even occur in combination. Here, we summarize how these two faces of protein misfolding contribute to the pathomechanisms of Alzheimer's disease, frontotemporal lobar degeneration, Parkinson's disease and prion diseases.
Loss-of-function mutations in the parkin gene (PARK2) and PINK1 gene (PARK6) are associated with autosomal recessive parkinsonism. PINK1 deficiency was recently linked to mitochondrial pathology in ...human cells and Drosophila melanogaster, which can be rescued by parkin, suggesting that both genes play a role in maintaining mitochondrial integrity. Here we demonstrate that an acute down-regulation of parkin in human SH-SY5Y cells severely affects mitochondrial morphology and function, a phenotype comparable with that induced by PINK1 deficiency. Alterations in both mitochondrial morphology and ATP production caused by either parkin or PINK1 loss of function could be rescued by the mitochondrial fusion proteins Mfn2 and OPA1 or by a dominant negative mutant of the fission protein Drp1. Both parkin and PINK1 were able to suppress mitochondrial fragmentation induced by Drp1. Moreover, in Drp1-deficient cells the parkin/PINK1 knockdown phenotype did not occur, indicating that mitochondrial alterations observed in parkin- or PINK1-deficient cells are associated with an increase in mitochondrial fission. Notably, mitochondrial fragmentation is an early phenomenon upon PINK1/parkin silencing that also occurs in primary mouse neurons and Drosophila S2 cells. We propose that the discrepant findings in adult flies can be explained by the time of phenotype analysis and suggest that in mammals different strategies may have evolved to cope with dysfunctional mitochondria.
Neurodegenerative diseases are characterized by the accumulation of misfolded proteins in the brain. Insights into protein quality control mechanisms to prevent neuronal dysfunction and cell death ...are crucial in developing causal therapies. Here, we report that various disease‐associated protein aggregates are modified by the linear ubiquitin chain assembly complex (LUBAC). HOIP, the catalytic component of LUBAC, is recruited to misfolded Huntingtin in a p97/VCP‐dependent manner, resulting in the assembly of linear polyubiquitin. As a consequence, the interactive surface of misfolded Huntingtin species is shielded from unwanted interactions, for example with the low complexity sequence domain‐containing transcription factor Sp1, and proteasomal degradation of misfolded Huntingtin is facilitated. Notably, all three core LUBAC components are transcriptionally regulated by Sp1, linking defective LUBAC expression to Huntington's disease. In support of a protective activity of linear ubiquitination, silencing of OTULIN, a deubiquitinase with unique specificity for linear polyubiquitin, decreases proteotoxicity, whereas silencing of HOIP has the opposite effect. These findings identify linear ubiquitination as a protein quality control mechanism and hence a novel target for disease‐modifying strategies in proteinopathies.
Synopsis
Misfolded proteins recruit the linear ubiquitin chain assembly complex (LUBAC) via p97/VCP, resulting in the assembly of linear ubiquitin chains at protein aggregates, such as Huntingtin with an polyQ expansion (Htt‐polyQ). This modification interferes with proteotoxicity of Htt‐polyQ by preventing sequestration of the transcription factor Sp1 and by promoting proteasomal degradation of misfolded Htt‐polyQ.
The linear ubiquitin chain assembly complex (LUBAC) is recruited to misfolded protein species, such as mutant Huntingtin, Ataxin‐3, SOD1, and TDP‐43.
Linear ubiquitination of mutant Huntingtin causes remodeling of its interactive surface.
Expression of LUBAC is dysregulated in Huntington's disease by sequestration of the transcription factor Sp1 to misfolded Huntingtin.
Linear ubiquitination promotes removal of misfolded protein species in a p97/VCP‐ and proteasome‐dependent manner.
Recruitment of the LUBAC E3 ligase, best known for its function in NF‐κB signalling, to protein aggregates for linear ubiquitin‐mediated removal of misfolded neurodegenerative disease proteins such as huntingtin, SOD1 or TDP‐43 exemplifies a new, potentially targetable cellular mechanism for controlling proteinopathies.
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