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Sökning: WFRF:(Ekman C. J.) > (2010-2014) > Stockholms universitet

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1.
  • Liu, X., et al. (författare)
  • Toward a minimal representation of aerosols in climate models : description and evaluation in the Community Atmosphere Model CAM5
  • 2012
  • Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 5:3, s. 709-739
  • Tidskriftsartikel (refereegranskat)abstract
    • A modal aerosol module (MAM) has been developed for the Community Atmosphere Model version 5 (CAM5), the atmospheric component of the Community Earth System Model version 1 (CESM1). MAM is capable of simulating the aerosol size distribution and both internal and external mixing between aerosol components, treating numerous complicated aerosol processes and aerosol physical, chemical and optical properties in a physically-based manner. Two MAM versions were developed: a more complete version with seven lognormal modes (MAM7), and a version with three lognormal modes (MAM3) for the purpose of long-term (decades to centuries) simulations. In this paper a description and evaluation of the aerosol module and its two representations are provided. Sensitivity of the aerosol lifecycle to simplifications in the representation of aerosol is discussed. Simulated sulfate and secondary organic aerosol (SOA) mass concentrations are remarkably similar between MAM3 and MAM7. Differences in primary organic matter (POM) and black carbon (BC) concentrations between MAM3 and MAM7 are also small (mostly within 10 %). The mineral dust global burden differs by 10 % and sea salt burden by 30-40 % between MAM3 and MAM7, mainly due to the different size ranges for dust and sea salt modes and different standard deviations of the log-normal size distribution for sea salt modes between MAM3 and MAM7. The model is able to qualitatively capture the observed geographical and temporal variations of aerosol mass and number concentrations, size distributions, and aerosol optical properties. However, there are noticeable biases; e.g., simulated BC concentrations are significantly lower than measurements in the Arctic. There is a low bias in modeled aerosol optical depth on the global scale, especially in the developing countries. These biases in aerosol simulations clearly indicate the need for improvements of aerosol processes (e.g., emission fluxes of anthropogenic aerosols and precursor gases in developing countries, boundary layer nucleation) and properties (e.g., primary aerosol emission size, POM hygroscopicity). In addition, the critical role of cloud properties (e. g., liquid water content, cloud fraction) responsible for the wet scavenging of aerosol is highlighted.
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2.
  • Kirkevag, A., et al. (författare)
  • Aerosol-climate interactions in the Norwegian Earth System Model-NorESM1-M
  • 2013
  • Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 6:1, s. 207-244
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of this study is to document and evaluate recent changes and updates to the module for aerosols and aerosol-cloud-radiation interactions in the atmospheric module CAM4-Oslo of the core version of the Norwegian Earth System Model (NorESM), NorESM1-M. Particular attention is paid to the role of natural organics, sea salt, and mineral dust in determining the gross aerosol properties as well as the anthropogenic contribution to these properties and the associated direct and indirect radiative forcing. The aerosol module is extended from earlier versions that have been published, and includes life-cycling of sea salt, mineral dust, particulate sulphate, black carbon, and primary and secondary organics. The impacts of most of the numerous changes since previous versions are thoroughly explored by sensitivity experiments. The most important changes are: modified prognostic sea salt emissions; updated treatment of precipitation scavenging and gravitational settling; inclusion of biogenic primary organics and methane sulphonic acid (MSA) from oceans; almost doubled production of land-based biogenic secondary organic aerosols (SOA); and increased ratio of organic matter to organic carbon (OM/OC) for biomass burning aerosols from 1.4 to 2.6. Compared with in situ measurements and remotely sensed data, the new treatments of sea salt and dust aerosols give smaller biases in near-surface mass concentrations and aerosol optical depth than in the earlier model version. The model biases for mass concentrations are approximately unchanged for sulphate and BC. The enhanced levels of modeled OM yield improved overall statistics, even though OM is still underestimated in Europe and overestimated in North America. The global anthropogenic aerosol direct radiative forcing (DRF) at the top of the atmosphere has changed from a small positive value to -0.08 W m(-2) in CAM4-Oslo. The sensitivity tests suggest that this change can be attributed to the new treatment of biomass burning aerosols and gravitational settling. Although it has not been a goal in this study, the new DRF estimate is closer both to the median model estimate from the AeroCom intercomparison and the best estimate in IPCC AR4. Estimated DRF at the ground surface has increased by ca. 60 %, to -1.89 W m(-2). We show that this can be explained by new emission data and omitted mixing of constituents between updrafts and downdrafts in convective clouds. The increased abundance of natural OM and the introduction of a cloud droplet spectral dispersion formulation are the most important contributions to a considerably decreased estimate of the indirect radiative forcing (IndRF). The IndRF is also found to be sensitive to assumptions about the coating of insoluble aerosols by sulphate and OM. The IndRF of -1.2 W m(-2), which is closer to the IPCC AR4 estimates than the previous estimate of -1.9 W m(-2), has thus been obtained without imposing unrealistic artificial lower bounds on cloud droplet number concentrations.
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3.
  • Axelsson, John, et al. (författare)
  • Effects of Sustained Sleep Restriction on Mitogen-Stimulated Cytokines, Chemokines and T Helper 1/T Helper 2 Balance in Humans
  • 2013
  • Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 8:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Recent studies suggest that acute sleep deprivation disrupts cellular immune responses by shifting T helper (Th) cell activity towards a Th2 cytokine profile. Since little is known about more long-term effects, we investigated how five days of sleep restriction would affect pro-inflammatory, chemotactic, Th1- and Th2 cytokine secretion. Methods: Nine healthy males participated in an experimental sleep protocol with two baseline sleep-wake cycles (sleep 23.00 - 07.00 h) followed by 5 days with restricted sleep (03.00 - 07.00 h). On the second baseline day and on the fifth day with restricted sleep, samples were drawn every third hour for determination of cytokines/chemokines (tumor necrosis factor alpha (TNF-alpha), interleukin (IL) -1 beta, IL-2, IL-4 and monocyte chemoattractant protein-1 (MCP-1)) after in vitro stimulation of whole blood samples with the mitogen phytohemagglutinin (PHA). Also leukocyte numbers, mononuclear cells and cortisol were analysed. Results: 5-days of sleep restriction affected PHA-induced immune responses in several ways. There was a general decrease of IL-2 production (p<.05). A shift in Th1/Th2 cytokine balance was also evident, as determined by a decrease in IL2/IL4 ratio. No other main effects of restricted sleep were shown. Two significant interactions showed that restricted sleep resulted in increased TNF-alpha and MCP-1 in the late evening and early night hours (p's<.05). In addition, all variables varied across the 24 h day. Conclusions: 5-days of sleep restriction is characterized by a shift towards Th2 activity (i.e. lower 1L-2/IL-4 ratio) which is similar to the effects of acute sleep deprivation and psychological stress. This may have implications for people suffering from conditions characterized by excessive Th2 activity like in allergic disease, such as asthma, for whom restricted sleep could have negative consequences. BAS AK, 1991, IMMUNOLOGICAL REVIEWS, V123, P5
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4.
  • Rådsten-Ekman, Maria, et al. (författare)
  • Case-study evaluation of a low and vegetated noise barrier in an urban public space
  • 2011
  • Ingår i: Proceedings of Inter-Noise 2011. - Osaka, Japan: : The Institute of Noise Control Engineering of Japan and the Acoustical Society of Japan.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • To improve the sound environment along a popular esplanade in Lyon, France, a 1 m high vegetated noise barrier was erected to protect against noise from an adjacent road. The barrier was made of a metallic structure, filled with a substrate on which 40 plants per square meter were grown on both sides. The effect of the barrier was evaluated by acoustic measurements conducted before and after the barrier was erected, as well as, by a questionnaire study in which pedestrians were asked to assess the sound environment both behind and at the side of the barrier. The barrier reduced the sound pressure level from about 67 to 62 dB (LAeq), at sitting height (1.2 m), 3.5 m from the roadside. Questionnaires responses (n = 349) from the same location showed that the barrier reduced road-traffic noise annoyance, and increased the overall quality of the sound environment by making it slightly calmer and slightly more pleasant. However, these effects were fairly small and the sound environment was still perceived as annoying by most of the respondents. Overall, the result thus suggested that the barrier made the sound environment better but not good. Further work will include detailed psychoacoustic analysis of the questionnaire data, as well as listening experiments using binaural recordings from the site.
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