| 1. |
- Mashayekhy Rad, Farshid, 1973-
(författare)
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Analytical methods for biomolecules involved in atmospheric aerosol formation in the Arctic
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the Arctic, increasing ice-free conditions and nutrients freed from the melting ice must strongly influence the marine life. Aerosol emissions from microbiological marine processes may affect the low clouds and fogs over the summer Arctic, which in turn have effects on the melting of sea ice. The radiative properties of the high Arctic low clouds are strongly dependent on the number concentration of airborne water-soluble particles, known as cloud condensation nuclei (CCN). If the effects of CCN on cloud optical properties is to be fully understood it is important to be able to specify the source and concentrations of the Arctic aerosol particles.Previous studies in the Arctic have indicated that organic material formed in the uppermost ocean surface is transferred to the atmosphere and plays a potentially very important role in the aerosol-fog/cloud cycle. However, many aspects of this process remain unverified and chemical characterisation of targeted groups of biomolecules is still notably fragmentary or non-existing. Investigation of biomolecules, particularly amino acids, peptides and proteins together with mono- and polysaccharides and fatty acids in the airborne aerosol, and their relative contributions to fog/cloud water, requires development of an array of “cutting edge” analytical techniques and methods.In this thesis, electrospray ionization mass spectrometry was used for all applications and target biomolecules. The measurements in the Arctic turned out to be challenging due to the highly complex, salty matrices, combined with very low concentration and high diversity of the target biomolecules, and each step of the analytical chain needed careful consideration. To increase the detectability of the very low levels of polysaccharides and proteins in aerosols, these compounds were hydrolyzed to their subunits, monosaccharides and amino acids. Monosaccharides were separated using hydrophilic interaction chromatography, which was beneficial for their detection in electrospray ionization mass spectrometry. Amino acids were derivatized, yielding improvement in reversed-phase chromatographic separation, ionization efficiency as well as selectivity. For fatty acids in a sea surface sample, a novel fast screening method was developed, utilizing travelling-wave ion mobility separation as an orthogonal technique connected to mass spectrometry. In addition, a method for the detection of wood burning as an anthropogenic source of aerosols was developed, utilizing anhydrous monosaccharides as markers. This method can be used in the upcoming expeditions for source apportionment studies.The results from the analyses of the aerosol and fog water samples, collected over the summer pack ice north of 80 °N, show that both total polysaccharides and total proteinaceous compounds (sum of proteins, peptides and amino acids) occurred at the pmol m-3 to nmol m-3 level. Interestingly, the levels were found higher between different years, suggested to be coupled to less ice coverage and thus to a higher biological activity in the ocean surface. The highest concentrations of polysaccharides, as an indication of marine polymer gels, were found during the summer over the pack ice area. In addition, a pilot source apportionment study was carried out combining the measurement of different molecular tracers, used as source markers. This study indicates the seasonality and abundance of marine polymer gels as an important feature of the Arctic Ocean connected to the melting and freezing of sea ice. It should be further studied how the abundance of these gels, which have a high potential for cloud droplet activation, affect the melting and freezing of the perennial sea ice.Given the successful development of analytical methods for targeted groups of biomolecules, this thesis has supported the importance of biomolecules as CCN and for cloud formation in the Arctic. Less ice coverage may further increase the number of biomolecular CCN which could change the radiative balance, by the formation of more low-level clouds. Overall, more studies are required to further unravel the complex relationship of biogenic sources, atmospheric chemistry and meteorology to assess the impact of climate change on the Arctic.
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| 2. |
- Bulatovic, Ines
(författare)
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Investigating aerosol effects on stratocumulus clouds through large-eddy simulation
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clouds have a large impact on Earth’s radiative budget by reflecting, absorbing and re-emitting radiation. They thus play a critical role in the climate system. Nevertheless, cloud radiative effects in a changing climate are highly uncertain. Atmospheric aerosol particles are another factor affecting Earth’s climate but the magnitude of their influence is also associated with high uncertainty. Therefore, an accurate representation of aerosol-cloud interactions in models is critical for having confidence in future climate projections. This thesis investigates aerosol impacts on cloud microphysical and radiative properties through numerical modelling, more specifically large-eddy simulation (LES). Moreover, the thesis investigates how the simulated cloud response to changes in the aerosol population depends on the model description of different processes. Mixed-phase stratocumulus (MPS) clouds are especially problematic to simulate for models on all scales. These clouds consist of a mixture of supercooled water and ice in the same volume and are therefore potentially thermodynamically unstable. MPS clouds over the central (north of 80° N) Arctic Ocean are particularly sensitive to aerosol changes due to the relatively clean atmospheric conditions in this region. At the same time, the clouds also have an important impact on the Arctic surface radiative budget. Therefore, this thesis mostly focuses on Arctic MPS clouds.Simulations of a typical subtropical marine stratocumulus cloud showed that the aerosol-cloud forcing depends on the model treatment for calculating the cloud droplet number concentration (CDNC). The simulated change in the top of the atmosphere shortwave radiation due to increased aerosol number concentrations was almost three times as large when the CDNC was prescribed compared to when the CDNC was prognostic. Simulations of a central Arctic summertime low-level MPS cloud confirmed that the chemical composition and the size of aerosol particles both can play an important role in determining the efficiency of an aerosol to act as cloud condensation nuclei - and thus influence cloud properties. However, the hygroscopicity of the aerosol particle was only important if the particles were small in size (i.e., if they correspond to the Aitken mode size) or if they were close to hydrophobic. Further, it was also found that Aitken mode particles can significantly change microphysical and radiative properties of central Arctic MPS if the concentration of larger particles (i.e., corresponding to the accumulation mode) is less than approximately 10-20 cm-3. One of the most recent research expeditions in the central Arctic (in the summer of 2018) was characterized by a high occurrence of multiple cloud layers. Namely, the boundary layer structure consisted of two MPS, one located close to the surface and one at the top of the boundary layer. Large-eddy simulations of an observed case with this particular cloud structure showed that the two-layer boundary-layer clouds are persistent unless the aerosol number concentrations are low (< 5 cm-3) or the wind speed is high (≥ 8.5 m s-1). In the model, low aerosol numbers led to a dissipation of the upper cloud layer while the lower cloud layer dissipated if the wind speed was strong. Changes in the optical thickness and cloud emissivity of each individual cloud layer of the two-layer cloud structure were found to substantially impact the surface radiative fluxes.
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| 3. |
- Widell, Bodil, 1972-
(författare)
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Development of GC-HRMS procedures for determination of naturally occuring polar compounds in various environmental applications
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall objectives of this dissertation were to gain further understanding of the two following environmentally significant issues: (i) Determination of natural steroid hormones in blood plasma from perch (Perca fluviatilis) during a reproductive cycle and to evaluate the possibility of using the steroid composition as a biomarker for early signs of endocrine disruptive effects. (ii) Determination of dissolved free amino acids in size resolved airborne particles collected over the Arctic pack ice area (>80°N) in summer and to study their overall relationship with the ocean surface microlayer as a potential source. This was made possible by the development of two separate gas chromatographic–high resolution mass spectrometry methods. To enable separation with gas chromatography both steroids and amino acids had to be chemically modified to increase their volatility. The small sample volumes available and low concentrations of analytes required a multi-step clean-up procedure to enable determination. The results showed that the circulating levels of steroids in perch varied over the year and that the levels of some androgens were lower in female perch exposed to leachate from a refuse dump compare to unexposed perch, which may explain the decline in fertility observed for the former group. This also indicated that the steroid composition in the blood plasma may function as a sensitive biomarker. The levels of dissolved free amino acids were enriched in the submicrometer aerosol, peaking in sizes around 100nm aerodynamic diameter. These findings do support a previous assumption that the most likely source for these particles is the surface microlayer of the open water between the ice floes. The most likely exchange mechanism of biogenic matter between ocean and atmosphere is the bursting of bubbles at the surface of the leads. This mechanism would provide a very important and poorly understood link between cloud radiative properties and marine biochemistry in the summer high Arctic (>80°N) through the production of cloud condensation nuclei.
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| 4. |
- Hamacher-Barth, Evelyne, 1962-
(författare)
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The high Arctic summer aerosol : Size, chemical composition, morphology and evolution over the pack-ice
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosol particles, especially in the high Arctic are still not very well represented in climate models. Particle size and number concentrations are strongly under-predicted and temporal variations of aerosol composition and size are still not very well understood, mainly due to the sparsity of observations.The main objective of this thesis is the characterization of the high Arctic summer aerosol by means of electron microscopy in order to extend the existing data set from previous expeditions by size resolved data on aerosol number, morphology and chemical composition and to gain a better understanding of the evolution of the aerosol in the atmosphere.Ambient aerosol was collected over the pack ice during the Arctic Summer Cloud and Ocean (ASCOS) campaign to the high Arctic in summer 2008. Aerosol particles were evaluated with scanning electron microscopy and subsequent digital image processing to assess particle size and morphology. More than 3900 aerosol particles from 9 sampling events were imaged with scanning electron microscopy and merged into groups of similar morphology which contributed to different degrees to the total aerosol: single particles (82%), gel particles (11%) and halo particles (7%). Single particles were observed over the whole size range with a maximum at 64 nm in diameter, gel particles appeared > 45 nm with a maximum in number at 174 nm, halo particles appeared > 75 nm with a maximum in number at 161 nm. The majority of particles showed the morphology of marine gels, no sea salt or otherwise crystalline particles were observed. Transmission electron microscopy enabled more subtle insights into particle morphology and allowed further subdivision of gel particles into aggregates, aggregates with film and mucus-like particles. Energy dispersive X-ray spectroscopy of individual particles revealed a gradual transition in the content of Na+/K+ and Ca2+/Mg2+ between particle morphologies. Single particles and aggregate particles preferentially contained Na+/K+ whereas aggregate with film particles and mucus-like particles mainly contained Ca2+/Mg2+ suggesting a connection between particle morphology and ion content. Back-trajectory analysis was used to identify aerosol sources and to understand the evolution of the aerosol as a function of the synoptic weather situation. Particle numbers, size and morphology changed with the days the air mass spent over the pack-ice. A morphological descriptor applied to gel particles showed a clear trend suggesting that the contour of the particles becomes sharper and more distinct with increased time spent over the pack-ice. For a very long time over the pack-ice, however, we observed a morphology comparable to freshly emitted particles suggesting aerosol sources over the inner pack-ice.Size resolved aerosol chemical composition measurements were utilized to investigate the inorganic composition of laboratory generated nascent sea spray aerosol particles and ambient aerosol samples collected during ASCOS. A significant enrichment of Ca2+ was observed in submicrometer particles in either case with a tendency for increasing Ca2+ enrichment with decreasing particle size. This has strong implications for the alkalinity of sea spray aerosol particles with consequences for the sulfur chemistry in the marine boundary layer, the hygroscopicity and thus the potential of sea spray aerosol particles to act as cloud condensation nuclei.
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| 5. |
- Hede, Thomas, 1975-
(författare)
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Beyond Köhler theory : Molecular dynamics simulations as a tool for atmospheric science
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the results from molecular dynamics (MD) simulations of nanoaerosol clusters are discussed. The connecting link of these studies is the Köhler theory, which is the theory of condensational growth and activation of cloud droplets to form clouds. By investigating parameters such as the surface tension, state of mixture and morphology of nanoaerosol particles, conclusions can be drawn to improve the Köhler theory to include the effects of organic compounds previously unaccounted for.For the terrestrial environment, the simulations show that the natural surfactant cis-pinonic acid, an oxidation product evaporated from boreal trees, spontaneously accumulates at the surface of nanoaerosol clusters and thereby reduces the surface tension. The surface tension depression is related to the concentration of the surfactant and the size of the clusters. Surface tension is an important parameter of the Köhler theory. A decrease of the surface tension can lower the critical water vapour supersaturation needed for cloud droplet activation, giving rise to more, but smaller cloud droplets (Twomey effect) which in turn could change the optical properties of the cloud. It was also shown that the three organic surfactants, being model compounds for so called Humic-like substances (HULIS) have the ability to form aggregates inside the nanoaerosol clusters. These HULIS aggregates can also promote the solubilization of hydrophobic organic carbon in the form of fluoranthene, enabling soot taking part in cloud drop formation.Dissolved intermediately surface-active free amino acids were shown to be of some relevance for cloud formation over remote marine areas. The MD simulations showed differences between the interacting forces for spherical and planar interfaces of amino acids solutions.This thesis has emphasized the surface-active properties of organic compounds, including model HULIS and amino acids and their effect on surface tension and molecular orientation including aggregate formation in nanoaerosol clusters and their activation to form droplets. This thesis shows that the Köhler equation does not fully satisfactory describe the condensational growth of nano-sized droplets containing organic surfactants. Different approaches are suggested as revisions of the Köhler theory.
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| 6. |
- Lundén, Jenny, 1971-
(författare)
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Atmospheric DMS in the High Arctic
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the Arctic summer when the anthropogenic influence is limited, the natural marine source of sulfur in the form of gas-phase dimethyl sulfide viz. DMS(g), is of great importance for cloud formation. The harsh environment of the Arctic makes it difficult to perform in situ measurements of DMS(g) and hence regional model simulations can serve as a complement to increase our understanding of DMS related processes in the Arctic. In this thesis a regional scale meteorological forecast model, extended with DMS(g) calculations, is used to provide a consistent three-dimensional time evolving picture of DMS(g) over the pack-ice region. The analysis focus on meteorological aspects on the horizontal and vertical distribution of DMS(g). Our results show that the amount of DMS(g) over an oceanic source region alone does not determine concentration found over the pack-ice, the prevailing wind also exerts a large influence on the horizontal DMS(g) distribution. The modeled DMS(g) concentrations are advected in plumes in over the pack-ice, which, in combination with the photo-chemical decay, explain the large observed temporal variability of DMS(g) over the pack-ice. The modeled vertical structure show episodes with DMS(g) maxima well above the local boundary layer. Also shown is that DMS(g) maxima can be formed adjacent to frontal zones. In the presence of turbulence DMS(g) can be mixed downwards into the local boundary layer and aid growth to local particles and hence contribute to cloud formation in the boundary layer.
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| 7. |
- Gao, Qiuju, 1966-
(författare)
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Marine biogenic polysaccharides as a potential source of aerosol in the high Arctic : Towards a link between marine biology and cloud formation
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Primary marine aerosol particles containing biogenic polymer microgels play a potential role for cloud formation in the pristine high Arctic summer. One of the major sources of the polymer gels in Arctic aerosol was suggested to be the surface water and more specifically, the surface microlayer (SML) of the open leads within the perennial sea ice as a result of bubble bursting at the air-sea interface. Phytoplankton and/or ice algae are believed to be the main origins of the polymer gels. In this thesis, we examine the chemical composition of biogenic polymers, with focus on polysaccharides, in seawater and airborne aerosol particles collected during the Arctic Summer Cloud Ocean Study (ASCOS) in the summer of 2008. The main results and findings include: A novel method using liquid chromatography coupling with tandem mass spectrometry was developed and applied for identification and quantification of polysaccharides. The enrichment of polysaccharides in the SML was shown to be a common feature of the Arctic open leads. Rising bubbles and surface coagulation of polymers are the likely mechanism for the accumulation of polysaccharides at the SML. The size dependencies of airborne polysaccharides on the travel-time since the last contact with the open sea are indicative of a submicron microgel source within the pack ice. The similarity of polysaccharides composition observed between the ambient aerosol particles and those generated by in situ bubbling experiments confines the microgel source to the open leads. The demonstrated occurrence of polysaccharides in surface sea waters and in air, with surface-active and hygroscopic properties, has shown their potential to serve as cloud condensation nuclei and subsequently promote cloud-drop activation in the pristine high Arctic. Presumably this possibility may renew interest in the complex but fascinating interactions between marine biology, aerosol, clouds and climate.
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