A long-term study of cloud residuals from low-level Arctic clouds
DownloadTo constrain uncertainties in radiative forcings associated with aerosol–cloud interactions, improved understanding of Arctic cloud formation is required, yet long-term measurements of the relevant cloud and aerosol properties remain sparse. We present the first long-term study of cloud residuals, i.e. particles that were involved in cloud formation and cloud processes, in Arctic low-level clouds measured at Zeppelin Observatory, Svalbard. To continuously sample cloud droplets and ice crystals and separate them from non-activated aerosol, a ground-based counter-flow virtual impactor inlet system (GCVI) was used. A detailed evaluation of the GCVI measurements, using concurrent cloud particle size distributions, meteorological parameters, and aerosol measurements, is presented for both warm and cold clouds, and the potential contribution of sampling artefacts is discussed in detail. We find an excellent agreement of the GCVI sampling efficiency of liquid clouds using two independent approaches. The 2-year data set of cloud residual size distributions and number concentrations reveals that the cloud residuals follow the typical seasonal cycle of Arctic aerosol, with a maximum concentration in spring and summer and a minimum concentration in the late autumn and winter months. We observed average activation diameters in the range of 58–78 nm for updraught velocities below 1 m s−1. A cluster analysis also revealed cloud residual size distributions that were dominated by Aitken mode particles down to around 20–30 nm. During the winter months, some of these small particles may be the result of ice, snow, or ice crystal shattering artefacts in the GCVI inlet; however, cloud residuals down to 20 nm in size were also observed during conditions when artefacts are less likely.
Using correlations between observed equivalent black carbon and aerosol size distribution to derive size resolved BC mass concentration: a method applied on long-term observations performed at Zeppelin station, Ny-Ålesund, Svalbard
The aim of this study was to explore particle size dependent properties by combining long-term observations
of equivalent black carbon (eBC) and number size distributions to investigate their correlation as function of
particle size. The work was conducted in two main parts. The first part consisted of a short laboratory
experiment to compare observed total particle light absorption (sigma_abs) with that observed according to particle
size by using a combination of a Differential Mobility Analyzer (DMA) and a Particle Soot Absorption
Photometer (PSAP). The laboratory study confirmed strong similarities between the observed and derived
r abs . In the second part the statistical approach using correlation between the r abs and the dN of each bin of
the number size distribution was tested on long-term data ranging from 2002 to 2010 observed at Zeppelin
station, Ny-Ålesund Svalbard. The data was clustered according to the number size distribution and grouped
in four major categories: Washout, Nucleation, Intermediate and Polluted. Each category presented different
features with respect to the derived eBC mass distributions, the Intermediate category showed similarities to
the few available Single Particle Soot Photometer (SP2) observations in the Arctic. Overall, the statistical
distribution of eBC, according to particle size, presented a larger dynamical range in the location of the
mode(s). To check for consistency, the eBC mass distributions were transformed into number based eBC size
distribution and compared to the observed total number size distribution. Whereas the Washout, Nucleation
and Intermediate categories presented plausible number distributions, the Polluted category displayed a mode
at small sizes (about 50nm) that was significantly exaggerated
Provningsjämförelse / Proficiency Test 2021-2, Suspenderat material och slam / Suspended solids and sludge
DownloadOverall health impacts of a potential increase in cycle commuting in Stockholm, Sweden.
Aims:To estimate the overall health impact of transferring commuting trips from car to bicycle.Methods:In this study registry information on the location of home and work for residents in Stockholm County was used to obtain the shortest travel route on a network of bicycle paths and roads. Current modes of travel to work were based on travel survey data. The relation between duration of cycling and distance cycled was established as a basis for selecting the number of individuals that normally would drive a car to work, but have a distance to work that they could bicycle within 30 minutes. The change in traffic flows was estimated by a transport model (LuTrans) and effects on road traffic injuries and fatalities were estimated by using national hospital injury data. Effects on air pollution concentrations were modelled using dispersion models.Results:Within the scenario, 111,000 commuters would shift from car to bicycle. On average the increased physical activity reduced the one-year mortality risk by 12% among the additional bicyclists. Including the number of years lost due to morbidity, the total number of disability adjusted life-years gained was 696. The amount of disability adjusted life-years gained in the general population due to reduced air pollution exposure was 471. The number of disability adjusted life-years lost by traffic injuries was 176. Also including air pollution effects among bicyclists, the net benefit was 939 disability adjusted life-years per year.Conclusions:Large health benefits were estimated by transferring commuting by car to bicycle.
The development of a miniaturised balloon-borne cloud water sampler and its first deployment in the high Arctic
DownloadThe chemical composition of cloud water can be used to infer the sources of particles upon which cloud droplets and ice crystals have formed. In order to obtain cloud water for analysis of chemical composition for elevated clouds in the pristine high Arctic, balloon-borne active cloud water sampling systems are the optimal approach. However, such systems have not been feasible to deploy previously due to their weight and the challenging environmental conditions. We have taken advantage of recent developments in battery technology to develop a miniaturised cloud water sampler for balloon-borne collection of cloud water. Our sampler is a bulk sampler with a cloud drop cutoff diameter of approximately 8mm and an estimated collection efficiency of 70%. The sampler was heated to prevent excessive ice accumulation and was able to operate for several hours under the extreme conditions encountered in the high Arctic. We have tested and deployed the new sampler on a tethered balloon during the Microbiology-Ocean-Cloud-Coupling in the High Arctic (MOCCHA) campaign in August and September 2018 close to the North pole. The sampler was able to successfully retrieve cloud water samples that were analysed to determine their chemical composition as well as their ice-nucleating activity. Given the pristine conditions found in the high Arctic we have placed significant emphasis on the development of a suitable cleaning procedure to minimise background contamination by the sampler itself.
Remobilization of terrestrial carbon across temporal and spatial scales deduced from the Arctic Ocean sediment record
DownloadArctic warming is expected to trigger large-scale environmental change including remobilization of terrestrial organic carbon (terrOC). Permafrost and peatland systems contain more than twice as much carbon as the atmosphere, and may upon destabilization expose large amounts of their carbon to microbial decomposition and release climate-forcing greenhouse gases (GHG). Remobilization of terrOC also causes lateral leakage of organic matter via Arctic rivers with further translocated organic matter degradation and GHG release, while a remainder is exported to the Arctic Ocean and re-deposited in sediments. Arctic Ocean sediments are thus receptors of terrOC remobilization for a large part of the circum-Arctic drainage basin, and offer an archive to study past terrOC remobilization, e.g. during warming periods of the last deglaciation.
This thesis investigates terrOC in Arctic Ocean sediments to study OC remobilization from permafrost and other terrestrial systems across temporal and spatial scales. As a first – historical – approach, permafrost OC remobilization and degradation during past warming episodes are studied using OC, dual-isotope source apportionment (13C-OC; 14C-OC) and terrestrial biomarkers (lignin phenols, long-chained n-alkanes and n-alkanoic acids) in glacial-cycle sediment cores from the Siberian continental margin. The results reveal that permafrost systems were highly vulnerable to OC release throughout past warming events, foremost during the Bølling–Allerød (14.7-12.9 kyr before present - BP) warming period and the early Holocene climate optimum (11.7-7.5 kyr BP). The sediment record shows that climate warming of about 1°C and 1.5°C (Northern Hemisphere) then triggered large-scale thawing of mostly coastal permafrost and permafrost soils in the Siberian hinterland. These results are consistent with the hypothesis that large-scale permafrost OC remobilization may have contributed to the observed rise in atmospheric CO2 during the last deglaciation, and thereby stresses the importance of permafrost thawing in the light of anthropogenic climate change.
The second – spatial – study angle in this thesis investigates the contemporary Earth system and studies terrOC remobilization from permafrost and other terrestrial sources using terrOC accumulation in surface sediments of the circum-Arctic shelf seas. This includes establishment and application of the Circum-Arctic Sediment Carbon Database (CASCADE), which is a data collection of thousands of observations of OC, 13C-OC, 14C-OC and terrestrial biomarkers from the published literature and yet-unpublished records. This offers the opportunity to study large-scale remobilization of terrOC in the circum-Arctic by integrating input from terrOC sources over large areas. Mass accumulation rates of the different terrOC sources (by 210Pb dating and dual-isotope source apportionment of OC) reveal that surface (incl. permafrost) soils remobilize more than twice as much terrOC as coastal erosion of old Pleistocene permafrost. Furthermore, vulnerabilities of terrOC stocks to large-scale remobilization are discussed, which suggests permafrost soils to be the most vulnerable terrOC pool to remobilization by climate warming.
This thesis highlights the vulnerability of terrOC stores to Arctic warming over time and space, and thus contributes to a better understanding of climate-carbon couplings in the Earth system.
Atmospheric ageing of inorganic sea spray aerosol: implications for hygroscopicity and cloud activation potential
DownloadSea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even
dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored.
We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial
decrease in hygroscopicity and cloud activation potential. The results point towards surface reactions that are more crucial
for small particles and the formation of salt structures with water bound within the aerosols, termed hydrates. Our findings
suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field
observations indicate a reduced hygroscopic growth of sub-micrometre SSA in the marine atmosphere compared to pure NaCl gfgddwhich is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for reduced
hygroscopicity and cloud activation potential.