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  • 151.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Numerical solutions of the macroscopic Maxwell equations for scattering by non-spherical particles: A tutorial review2016In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 178, p. 22-37Article in journal (Refereed)
    Abstract [en]

    Numerical solution methods for electromagnetic scattering by non-spherical particles comprise a variety of different techniques, which can be traced back to different assumptions and solution strategies applied to the macroscopic Maxwell equations. One can distinguish between time- and frequency-domain methods; further, one can divide numerical techniques into finite-difference methods (which are based on approximating the differential operators), separation-of-variables methods (which are based on expanding the solution in a complete set of functions, thus approximating the fields), and volume integral-equation methods (which are usually solved by discretisation of the target volume and invoking the long-wave approximation in each volume cell). While existing reviews of the topic often tend to have a target audience of program developers and expert users, this tutorial review is intended to accommodate the needs of practitioners as well as novices to the field. The required conciseness is achieved by limiting the presentation to a selection of illustrative methods, and by omitting many technical details that are not essential at a first exposure to the subject. On the other hand, the theoretical basis of numerical methods is explained with little compromises in mathematical rigour; the rationale is that a good grasp of numerical light scattering methods is best achieved by understanding their foundation in Maxwell's theory. (C) 2015 Elsevier Ltd. All rights reserved.

  • 152.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Numerically exact computation of the optical properties of light absorbing carbon aggregates for wavelength of 200 nm-12.2 mu m2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 17, p. 8319-8329Article in journal (Refereed)
    Abstract [en]

    The optical properties of externally mixed light absorbing carbon (LAC) aggregates are computed over the spectral range from 200 nm-12.2 mu m by use of the numerically exact superposition T-matrix method. The spectral computations are tailored to the 14-band radiation model employed in the Integrated Forecasting System operated at the European Centre for Medium Range Weather Forecast. The size- and wavelength dependence of the optical properties obtained with the fractal aggregate model differs significantly from corresponding results based on the homogeneous sphere approximation, which is still commonly employed in climate models. The computational results are integrated into the chemical transport model MATCH (Multiple-scale Atmospheric Transport and CHemistry modelling system) to compute 3-D fields of size-averaged aerosol optical properties. Computational results obtained with MATCH are coupled to a radiative transfer model to compute the shortwave radiative impact of LAC. It is found that the fractal aggregate model gives a shortwave forcing estimate that is twice as high as that obtained with the homogeneous sphere approximation. Thus previous estimates based on the homogeneous sphere model may have substantially underestimated the shortwave radiative impact of freshly emitted LAC.

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  • 153.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    On the Discrepancy between Modeled and Measured Mass Absorption Cross Sections of Light Absorbing Carbon Aerosols2010In: Aerosol Science and Technology, ISSN 0278-6826, E-ISSN 1521-7388, Vol. 44, no 6, p. 453-460Article in journal (Refereed)
    Abstract [en]

    Recent modeling studies based on the Rayleigh-Debye-Gans (RDG) approximation have revealed a discrepancy between modeled and measured mass absorption cross sections (MAC) for atmospheric light absorbing carbon (LAC) aerosols. One plausible explanation is that this discrepancy is due to errors introduced by neglecting electromagnetic interactions among monomers in LAC aggregates within the RDG approximation. Here we compute MAC by use of numerically exact solutions to Maxwell's equations and investigate the sensitivity of the results to a variation in the aggregates' physical properties and refractive index. The results do confirm that approximate methods can introduce large errors in the results for the optical properties. However, these errors alone cannot explain the discrepancy between measured and modeled values of MAC. An agreement between observations and theoretical results can only be attained when assuming a fairly high value of the real and imaginary parts of the refractive index along the void-fraction curve and a mass density not exceeding 1.5-1.7 g/cm3.

  • 154.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    On the observability of chemical and physical aerosol properties by optical observations: Inverse modelling with variational data assimilation2009In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 61, no 5, p. 747-755Article in journal (Refereed)
    Abstract [en]

    Determining size-resolved chemical composition of aerosols is important for modelling the aerosols' direct and indirect climate impact, for source-receptor modelling, and for understanding adverse health effects of particulate pollutants. Obtaining this kind of information from optical remote sensing observations is an ill-posed inverse problem. It can be solved by variational data assimilation in conjunction with an aerosol transport model. One important question is how much information about the particles' physical and chemical properties is contained in the observations. We perform a numerical experiment to test the observability of size-dependent aerosol composition by remote sensing observations. An aerosol transport model is employed to produce a reference and a perturbed aerosol field. The perturbed field is taken as a proxy for a background estimate subject to uncertainties. The reference result represents the 'true' state of the system. Optical properties are computed from the reference results and are assimilated into the perturbed model. The assimilation results reveal that inverse modelling of optical observations significantly improves the background estimate. However, the optical observations alone do not contain sufficient information for producing a faithful retrieval of the size-resolved aerosol composition. The total mass mixing ratios, on the other hand, are retrieved with remarkable accuracy.

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  • 155.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Optical properties of black carbon aerosols encapsulated in a shell of sulfate: comparison of the closed cell model with a coated aggregate model2017In: Optics Express, E-ISSN 1094-4087, Vol. 25, no 20, p. 24579-24593Article in journal (Refereed)
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  • 156.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    The T-matrix code Tsym for homogeneous dielectric particles with finite symmetries2013In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 123, p. 62-78Article in journal (Refereed)
    Abstract [en]

    A T-matrix code tailored to non-axisymmetric particles with finite symmetries is described. The code exploits geometric symmetries of particles by use of group theoretical methods. Commutation relations of the T-matrix are implemented for reducing CPU-time requirements. Irreducible representations of finite groups are employed for alleviating ill-conditioning problems in numerical computations. Further, an iterative T-matrix method for particles with small-scale surface perturbations is implemented. The code can compute both differential and integrated optical properties of particles in,either fixed or random orientation. Methods for testing the convergence and correctness of the computational results are discussed. The package also includes a database of pre-computed group-character tables, as well as an interface to the GAP programming language for computational group theory. The code can be downloaded at http://www.rss.chalmers.se/similar to kahnert/Tsym.html. (C) 2013 Elsevier Ltd. All rights reserved.

  • 157.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    T-matrix computations for particles with high-order finite symmetries2013In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 123, p. 79-91Article in journal (Refereed)
    Abstract [en]

    The use of group theoretical methods can substantially reduce numerical ill-conditioning problems in T-matrix computations. There are specific problems related to obtaining the irreducible characters of high-order symmetry groups and to the construction of a transformation from the basis of vector spherical wave functions to the irreducible basis of high-order symmetry groups. These problems are addressed, and numerical solutions are discussed and tested. An important application of the method is non-convex particles perturbed with high-order polynomials. Such morphologies can serve as models for particles with small-scale surface roughness, such as mineral aerosols, atmospheric ice particles with rimed surfaces, and various types of cosmic dust particles. The method is tested for high-order 3D-Chebyshev particles, and the performance of the method is gauged by comparing the results to computations based on iteratively solving a Lippmann-Schwinger T-matrix equation. The latter method trades ill-conditioning problems for potential slow-convergence problems, and it is rather specific, as it is tailored to particles with small-scale surface roughness. The group theoretical method is general and not plagued by slow-convergence problems. The comparison of results shows that both methods achieve a comparable numerical stability. This suggests that for particles with high-order symmetries the group-theoretical approach is able to overcome the illconditioning problems. Remaining numerical limitations are likely to be associated with loss-of-precision problems in the numerical evaluation of the surface integrals. (C) 2012 Elsevier Ltd. All rights reserved.

  • 158.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Variational data analysis of aerosol species in a regional CTM: background error covariance constraint and aerosol optical observation operators2008In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, no 5, p. 753-770Article in journal (Refereed)
    Abstract [en]

    A multivariate variational data assimilation scheme for the Multiple-scale Atmospheric Transport and CHemistry (MATCH) model is presented and tested. A spectral, non-separable approach is chosen for modelling the background error constraints. Three different methods are employed for estimating background error covariances, and their analysis performances are compared. Observation operators for aerosol optical parameters are presented for externally mixed particles. The assimilation algorithm is tested in conjunction with different background error covariance matrices by analysing lidar observations of aerosol backscattering coefficient. The assimilation algorithm is shown to produce analysis increments that are consistent with the applied background error statistics. Secondary aerosol species show no signs of chemical relaxation processes in sequential assimilation of lidar observations, thus indicating that the data analysis result is well balanced. However, both primary and secondary aerosol species display emission- and advection-induced relaxations.

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  • 159.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Andersson, Emma
    How much information do extinction and backscattering measurements contain about the chemical composition of atmospheric aerosol?2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 5, p. 3423-3444Article in journal (Refereed)
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  • 160.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Kanngiesser, Franz
    Aerosol optics model for black carbon applicable to remote sensing, chemical data assimilation, and climate modelling2021In: Optics Express, E-ISSN 1094-4087, Vol. 29, no 7, p. 10639-10658Article in journal (Refereed)
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    Aerosol optics model for black carbon applicable to remote sensing, chemical data assimilation, and climate modelling
  • 161.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Kanngiesser, Franz
    Modelling optical properties of atmospheric black carbon aerosols2020In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 244, article id UNSP 106849Article in journal (Refereed)
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  • 162.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Kanngiesser, Franz
    Jarvinen, Emma
    Schnaiter, Martin
    Aerosol-optics model for the backscatter depolarisation ratio of mineral dust particles2020In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 254, article id 107177Article in journal (Refereed)
    Abstract [en]

    The size-dependence of the linear depolarisation ratio of mineral dust aerosols is investigated. Laboratory measurements on 131 different aerosol samples with varying size distributions and mineralogical compositions are fitted with a homogeneous spheroid model. A minimum-bias and minimum-variance fit of the data is obtained for prolate model particles with a refractive index of 1.525+0.001i and an aspect ratio of 0.87. The model error is analysed by varying the input parameters to the light-scattering computations. It is found that the scattering of the measurements about the model can mainly be explained by variation of the morphology and dielectric properties, and to a much lesser extent by variation in the geometric standard deviation of the size distribution. The modelling of the data is extended by using size-shape distributions of spheroids. The results indicate that there is some freedom in choosing the best-fit weights of the shape-distribution of spheroids, which could potentially be useful when extending the model to multiple wavelengths, or to including additional optical parameters other than depolarisation. However, it is also found that the most reasonable fits of the data are obtained by mildly aspherical prolate and oblate spheroids, which limits the freedom of adjusting the best-fit weights. (C) 2020 The Authors. Published by Elsevier Ltd.

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  • 163.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, T
    Uncertainties in measured and modelled asymmetry parameters of mineral dust aerosols2006In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 100, no 1-3, p. 173-178Article in journal (Refereed)
    Abstract [en]

    The error caused by the uncertainty in the refractive index in the determination of the asymmetry parameter g is studied for a variety of mineral dust aerosol samples at two different optical wavelengths. Lorenz-Mie computations for spherical model particles are compared with results based on laboratory-measured phase functions in conjunction with a commonly used extrapolation method. The difference between the g-value based on measurements and the g-value based on Lorenz-Mie simulations is generally on the same order of magnitude as the error caused by the uncertainty in the refractive index m. For larger effective radii the error in g related to the use of spherical model particles is even larger than that related to the uncertainty in in. This indicates that the use of spherical model particles can be among the major error sources in the determination of the asymmetry parameter of dust aerosols. (c) 2005 Elsevier Ltd. All rights reserved.

  • 164.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, T.
    Raisanen, P.
    Mie simulations as an error source in mineral aerosol radiative forcing calculations2007In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 133, no 623, p. 299-307Article in journal (Refereed)
    Abstract [en]

    The role of aerosols remains a major uncertainty for climate and climate change. For the direct radiative forcing by mineral aerosols, the uncertainty in the refractive index in has been regarded as the most important error source, while the impact of aerosol non-sphericity has been considered a minor issue and is neglected in climate models. Here, the errors caused by the spherical particle approximation (SPA) are evaluated by comparing radiative fluxes based on (i) Mie simulations and (ii) laboratory measurements of aerosol optical properties. Furthermore, they are contrasted with the errors related to the uncertainty in the refractive index. These two error sources are found to be of comparable magnitude, although they are strongly dependent on optical depth, surface albedo, and particle size. Thus, our results provide evidence that, contrary to common beliefs, the use of spherical model particles in radiative transfer simulations is probably among the major sources of error in quantifying the climate forcing effect of mineral aerosols. This stems from misrepresentation of the scattering phase function and the asymmetry parameter. Aerosol single-scattering computations based on non-spherical model particles are expected to reduce the shape-related errors and thus significantly improve the accuracy of radiative forcing simulations. Copyright (c) 2007 Royal Meteorological Society.

  • 165.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, T
    Veihelmann, B
    Spherical and spheroidal model particles as an error source in aerosol climate forcing and radiance computations: A case study for feldspar aerosols2005In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 110, no D18, article id D18S13Article in journal (Refereed)
    Abstract [en]

    A case study for feldspar aerosols is conducted to assess the errors introduced by simple model particles in radiance and flux simulations. The spectral radiance field and net flux are computed for a realistic phase function of feldspar aerosols measured in the laboratory at 633 nm. Results are compared to computations with spherical and spheroidal model particles. It is found that the use of spherical model particles introduces large spectral radiance errors at top of atmosphere (TOA) between -6 and 31%. Using a new shape parameterization of spheroids reduces the error range to -1 to 6%. Spherical model particles yield an absolute TOA spectral net flux error of -6.1 mW m(-2) nm(-1). An equiprobable shape distribution of spheroids results in only minor improvements, but the new shape parameterization yields an error of only -0.8 mW m(-2) nm(-1). A variation of the refractive index m reveals that the resulting changes in the TOA spectral net flux are slightly smaller than the error caused by assuming the particles to be spherical. However, the uncertainty of m is commonly considered the major error source in aerosol radiative forcing simulations, whereas the use of spherical model particles is often not seriously questioned. This study implies that this notion needs to be reconsidered. Should the relative spectral net flux errors be representative for the entire spectrum, then the use of spherical model particles may be among the major error sources in broadband flux simulations. The new spheroidal shape parameterization can, however, substantially improve the results.

  • 166.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Variational data-analysis method for combining laboratory-measured light-scattering phase functions and forward-scattering computations2007In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 103, no 1, p. 27-42Article in journal (Refereed)
    Abstract [en]

    A method is developed based on the variational data-analysis formalism to combine laboratory-measured scattering phase functions with forward-scattering phase function computations based on independent size distribution (SD) measurements. The algorithm yields an optimal estimate of the true phase function of the system that is not only based on the measurements and the computational results but also on all available information of the error variances and, if applicable, error covariances of the measured and computed phase functions. The high flexibility of the method is demonstrated by applying it to phase functions of feldspar and fly ash aerosols. Further, the algorithm is employed to determine the asymmetry parameter g of nine different mineral aerosol samples at two different optical wavelengths, and to assess the relative importance of different error sources in the determination of g. It is found that the use of spherical model particles in simulations of g can result in errors on the same order of magnitude as the uncertainty of the refractive index. The use of spherical model particles in computations of forward scattering, however, is found to be only a minor error source. (c) 2006 Elsevier Ltd. All rights reserved.

  • 167.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Lindqvist, Hannakaisa
    Models for integrated and differential scattering optical properties of encapsulated light absorbing carbon aggregates2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 7, p. 7974-7993Article in journal (Refereed)
    Abstract [en]

    Optical properties of light absorbing carbon (LAC) aggregates encapsulated in a shell of sulfate are computed for realistic model geometries based on field measurements. Computations are performed for wavelengths from the UV-C to the mid-IR. Both climate- and remote sensing-relevant optical properties are considered. The results are compared to commonly used simplified model geometries, none of which gives a realistic representation of the distribution of the LAC mass within the host material and, as a consequence, fail to predict the optical properties accurately. A new core-gray shell model is introduced, which accurately reproduces the size- and wavelength dependence of the integrated and differential optical properties. (C) 2013 Optical Society of America

  • 168.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Lindqvist, Hannakaisa
    Review: Model particles in atmospheric optics2014In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 146, p. 41-58Article, review/survey (Refereed)
    Abstract [en]

    This review paper provides an overview over model geometries for computing light scattering by small particles. The emphasis is on atmospheric optics, although much of this review will also be relevant to neighbouring fields, in particular to astronomy. Various morphological particle properties are discussed, such as overall nonsphericity, pristine shapes, aggregation, and different forms of inhomogeneity, e.g. porous and compact inhomogeneous morphologies, as well as encapsulated aggregates. Models employed to reproduce the optical properties of complex particles range from strongly simplified to highly realistic and morphologically sophisticated model geometries. Besides reviewing the most recent literature, we discuss the idea behind models of varying degree of complexity with regard to the intended use of the models. Applications range from fundamental studies of light scattering processes to routine applications of particle optics look-up tables in operational modelling systems. (C) 2014 Elsevier Ltd. All rights reserved.

  • 169.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Lindqvist, Hannakaisa
    Ebert, Martin
    Optical properties of light absorbing carbon aggregates mixed with sulfate: assessment of different model geometries for climate forcing calculations2012In: Optics Express, E-ISSN 1094-4087, Vol. 20, no 9Article in journal (Refereed)
    Abstract [en]

    Light scattering by light absorbing carbon (LAC) aggregates encapsulated into sulfate shells is computed by use of the discrete dipole method. Computations are performed for a UV, visible, and IR wavelength, different particle sizes, and volume fractions. Reference computations are compared to three classes of simplified model particles that have been proposed for climate modeling purposes. Neither model matches the reference results sufficiently well. Remarkably, more realistic core-shell geometries fall behind homogeneous mixture models. An extended model based on a core-shell-shell geometry is proposed and tested. Good agreement is found for total optical cross sections and the asymmetry parameter. (C) 2012 Optical Society of America

  • 170.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Markkanen, Johannes
    Morphological models for inhomogeneous particles: Light scattering by aerosols, cometary dust, and living cells2016In: Light Scattering Reviews, Volume 11: Light Scattering and Radiative Transfer / [ed] Kokhanovsky, Alexander, Berlin: Springer , 2016, 2, p. 299-337Chapter in book (Refereed)
  • 171.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Mauno, Paivi
    On the impact of non-sphericity and small-scale surface roughness on the optical properties of hematite aerosols2011In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 112, no 11, p. 1815-1824Article in journal (Refereed)
    Abstract [en]

    We perform a comparative modelling study to investigate how different morphological features influence the optical properties of hematite aerosols. We consider high-order Chebyshev particles as a proxy for aerosol with a small-scale surface roughness, and spheroids as a model for nonspherical aerosols with a smooth boundary surface. The modelling results are compared to those obtained for homogeneous spherical particles. It is found that for hematite particles with an absorption efficiency of order unity the difference in optical properties between spheres and spheroids disappears. For optically softer particles, such as ice particles at far-infrared wavelengths, this effect can be observed for absorption efficiencies lower than unity. The convergence of the optical properties of spheres and spheroids is caused by absorption and quenching of internal resonances inside the particles, which depend both on the imaginary part of the refractive index and on the size parameter, and to some extent on the real part of the refractive index. By contrast, small-scale surface roughness becomes the dominant morphological feature for large particles. This effect is likely to depend on the amplitude of the surface roughness, the relative significance of internal resonances, and possibly on the real part of the refractive index. The extinction cross section is rather insensitive to surface roughness, while the single-scattering albedo, asymmetry parameter, and the Mueller matrix are strongly influenced. Small-scale surface roughness reduces the backscattering cross section by up to a factor of 2-3 as compared to size-equivalent particles with a smooth boundary surface. This can have important implications for the interpretation of lidar backscattering observations. (C) 2011 Elsevier Ltd. All rights reserved.

  • 172.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Mauno, Paivi
    On the impact of non-sphericity and small-scale surface roughness on the optical properties of hematite aerosols (vol 112, pg 1815, 2011)2012In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 113, no 1, p. 117-117Article in journal (Refereed)
  • 173.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    Tyynela, Jani
    Light scattering by particles with small-scale surface roughness: Comparison of four classes of model geometries2012In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 113, no 18, p. 86-97Article in journal (Refereed)
    Abstract [en]

    We compare four different model geometries for particles with small-scale surface roughness. The geometries are based on regular and stochastic surface perturbations, as well as on 2D- and 3D-roughness models. We further compare T-matrix and discrete dipole computations. Particle size parameters of 5 and 50 are considered, as well as refractive indices of 1.6+0.0005i and 3+0.1i. The effect of small-scale surface roughness on the intensity and polarisation of the scattered light strongly depends on the size parameter and refractive index. In general, 2D surface roughness models predict stronger effects than 3D models. Stochastic surface roughness models tend to predict the strongest depolarising effects, while regular surface roughness models can have a stronger effect on the angular distribution of the scattered intensity. Computations with the discrete dipole approximation only cover a limited range of size parameters. T-matrix computations allow us to significantly extend that range, but at the price of restricting the model particles to symmetric surface perturbations with small amplitudes. (C) 2012 Elsevier Ltd. All rights reserved.

  • 174.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Rother, Tom
    Convergence of the iterative T-matrix method2020In: Optics Express, E-ISSN 1094-4087, Vol. 28, no 19, p. 28269-28282Article in journal (Refereed)
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  • 175.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Rother, Tom
    Electromagnetic Wave Scattering on Nonspherical Particles: Basic Methodology and Simulations2014 (ed. 2)Book (Other academic)
  • 176.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Rother, Tom
    Modeling optical properties of particles with small-scale surface roughness: combination of group theory with a perturbation approach2011In: Optics Express, E-ISSN 1094-4087, Vol. 19, no 12, p. 11138-11151Article in journal (Refereed)
    Abstract [en]

    A T-matrix method for scattering by particles with small-scale surface roughness is presented. The method combines group theory with a perturbation expansion approach. Group theory is found to reduce CPU-time by 4-6 orders of magnitude. The perturbation expansion extends the range of size parameters by a factor of 5 compared to non-perturbative methods. An application to optically hard particles shows that small-scale surface roughness changes scattering in side-and backscattering directions, and it impacts the single-scattering albedo. This can have important implications for interpreting remote sensing observations, and for the climate impact of mineral aerosols. (C) 2011 Optical Society of America

  • 177.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Sandvik, Anne Dagrun
    Biryulina, Marina
    Stamnes, Jakob J.
    Stamnes, Knut
    Impact of ice particle shape on short-wave radiative forcing: A case study for an arctic ice cloud2008In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 109, no 7, p. 1196-1218Article in journal (Refereed)
    Abstract [en]

    We used four different non-spherical particle models to compute optical properties of an arctic ice cloud and to simulate corresponding cloud radiative forcings and fluxes. One important finding is that differences in cloud forcing, downward flux at the surface, and absorbed flux in the atmosphere resulting from the use of the four different ice cloud particle models are comparable to differences in these quantities resulting from changing the surface albedo from 0.4 to 0.8, or by varying the ice water content (IWC) by a factor of 2. These findings show that the use of a suitable non-spherical ice cloud particle model is very important for a realistic assessment of the radiative impact of arctic ice clouds. The differences in radiative broadband fluxes predicted by the four different particle models were found to be caused mainly by differences in the optical depth and the asymmetry parameter. These two parameters were found to have nearly the same impact on the predicted cloud forcing. Computations were performed first by assuming a given vertical profile of the particle number density, then by assuming a given profile of the IWC. In both cases, the differences between the cloud radiative forcings computed with the four different non-spherical particle models were found to be of comparable magnitude. This finding shows that precise knowledge of ice particle number density or particle mass is not sufficient for accurate prediction of ice cloud radiative forcing. It is equally important to employ a non-spherical shape model that accurately reproduces the ice particle's dimension-to-volume ratio and its asymmetry parameter. The hexagonal column/plate model with air-bubble inclusions seems to offer the highest degree of flexibility. (c) 2007 Elsevier Ltd. All rights reserved.

  • 178.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Scheirer, Ronald
    SMHI, Research Department, Atmospheric remote sensing.
    Multiple scattering by aerosols as seen from CALIPSO - a Monte-Carlo modelling study2019In: Optics Express, E-ISSN 1094-4087, Vol. 27, no 23, p. 33684-33700Article in journal (Refereed)
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  • 179. Kanngiesser, Franz
    et al.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Calculation of optical properties of light-absorbing carbon with weakly absorbing coating: A model with tunable transition from film-coating to spherical-shell coating2018In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 216, p. 17-36Article in journal (Refereed)
  • 180. Kanngiesser, Franz
    et al.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Coating material-dependent differences in modelled lidar-measurable quantities for heavily coated soot particles2019In: Optics Express, E-ISSN 1094-4087, Vol. 27, no 25, p. 36368-36387Article in journal (Refereed)
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  • 181. Kanngiesser, Franz
    et al.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Modeling Optical Properties of Non-Cubical Sea-Salt Particles2021In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 126, no 4, article id e2020JD033674Article in journal (Refereed)
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    Modeling Optical Properties of Non-Cubical Sea-Salt Particles
  • 182. Kanngiesser, Franz
    et al.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Optical properties of water-coated sea salt model particles2021In: Optics Express, E-ISSN 1094-4087, Vol. 29, no 22, p. 34926-34950Article in journal (Refereed)
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    Optical properties of water-coated sea salt model particles
  • 183. Karlsson, Per Erik
    et al.
    Klingberg, Jenny
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Andersson, Camilla
    SMHI, Research Department, Air quality.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Karlsson, Gunilla Pihl
    Pleijel, Hakan
    Past, present and future concentrations of ground-level ozone and potential impacts on ecosystems and human health in northern Europe2017In: SCIENCE OF THE TOTAL ENVIRONMENT, ISSN 0048-9697, Vol. 576, p. 22-35Article in journal (Refereed)
  • 184. Kauhaniemi, M.
    et al.
    Kukkonen, J.
    Harkonen, J.
    Nikmo, J.
    Kangas, L.
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    Ketzel, M.
    Kousa, A.
    Haakana, M.
    Karppinen, A.
    Evaluation of a road dust suspension model for predicting the concentrations of PM10 in a street canyon2011In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 45, no 22, p. 3646-3654Article in journal (Refereed)
    Abstract [en]

    We have slightly refined, evaluated and tested a mathematical model for predicting the vehicular suspension emissions of PM10. The model describes particulate matter generated by the wear of road pavement, traction sand, and the processes that control the suspension of road dust particles into the air. However, the model does not address the emissions from the wear of vehicle components. The performance of this suspension emission model has been evaluated in combination with the street canyon dispersion model OSPM. We used data from a measurement campaign that was conducted in the street canyon Runeberg Street in Helsinki from 8 January to 2 May, 2004. The model reproduced fairly well the seasonal variation of the PM10 concentrations, also during the time periods, when studded tyres and anti-skid treatments were commonly in use. For instance, the index of agreement (IA) was 0.83 for the time series of the hourly predicted and observed concentrations of PM10. The predictions of the model were found to be sensitive to precipitation and street traction sanding. The main uncertainties in the predictions are probably caused by (i) the cleaning processes of the streets, which are currently not included in the model, (ii) the uncertainties in the estimation of the sanding days, and (iii) the uncertainties in the evaluation of precipitation. This study provides more confidence that this model could potentially be a valuable tool of assessment to evaluate and forecast the suspension PM10 emissions worldwide. However, a further evaluation of the model is needed against other datasets in various vehicle fleet, speed and climatic conditions. (C) 2011 Elsevier Ltd. All rights reserved.

  • 185. Kauhaniemi, M.
    et al.
    Stojiljkovic, A.
    Pirjola, L.
    Karppinen, A.
    Harkonen, J.
    Kupiainen, K.
    Kangas, L.
    Aarnio, M. A.
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    Denby, B. R.
    Kukkonen, J.
    Comparison of the predictions of two road dust emission models with the measurements of a mobile van2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 17, p. 9155-9169Article in journal (Refereed)
    Abstract [en]

    The predictions of two road dust suspension emission models were compared with the on-site mobile measurements of suspension emission factors. Such a quantitative comparison has not previously been reported in the reviewed literature. The models used were the Nordic collaboration model NORTRIP (NOn-exhaust Road TRaffic Induced Particle emissions) and the Swedish-Finnish FORE model (Forecasting Of Road dust Emissions). These models describe particulate matter generated by the wear of road surface due to traction control methods and processes that control the suspension of road dust particles into the air. An experimental measurement campaign was conducted using a mobile laboratory called SNIFFER, along two selected road segments in central Helsinki in 2007 and 2008. The suspended PM10 concentration was measured behind the left rear tyre and the street background PM10 concentration in front of the van. Both models reproduced the measured seasonal variation of suspension emission factors fairly well during both years at both measurement sites. However, both models substantially under-predicted the measured emission values. The article illustrates the challenges in conducting road suspension measurements in densely trafficked urban conditions, and the numerous requirements for input data that are needed for accurately applying road suspension emission models.

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  • 186. Kchalchenkov, Aleksander
    et al.
    Kovalets, Ivan
    Asker, Christian
    SMHI, Research Department, Air quality.
    Lavrova, Tatiana
    Todosienko, Sergey
    Avila, Rodolfo
    APPLICATION OF THE COMPLEX OF ATMOSPHERIC TRANSPORT MODELS FOR ASSESSMENT OF IMPACT ON THE ENVIRONMENT OF THE TERRITORIES OF FORMER URANIUM PRODUCTION2017Conference paper (Refereed)
  • 187. Ketzel, Matthias
    et al.
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    Johansson, Christer
    Duering, Ingo
    Pohjolar, Mia
    Oettl, Dietmar
    Gidhagen, Lars
    SMHI, Research Department, Air quality.
    Wahlin, Peter
    Lohmeyer, Achim
    Haakana, Mervi
    Berkowicz, Ruwim
    Estimation and validation of PM2.5/PM10 exhaust and non-exhaust emission factors for practical street pollution modelling2007In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 41, no 40, p. 9370-9385Article in journal (Refereed)
    Abstract [en]

    In order to carry out efficient traffic and air quality management, validated models and PM emission estimates are needed. This paper compares current available emission factor estimates for PM10 and PM2.5 from emission databases and different emission models, and validates these against eight high quality street pollution measurements in Denmark, Sweden, Germany, Finland and Austria. The data sets show large variation of the PM concentration and emission factors with season and with location. Consistently at all roads the PM10 and PM2.5 emission factors are lower in the summer month than the rest of the year. For example, PM10 emission factors are in average 5-45% lower during the month 6-10 compared to the annual average. The range of observed total emission factors (including non-exhaust emissions) for the different sites during summer conditions are 80-130mgkm(-1) for PM10, 30-60mgkm(-1) for PM2.5 and 20-50mgkm(-1) for the exhaust emissions. We present two different strategies regarding modelling of PM emissions: (1) For Nordic conditions with strong seasonal variations due to studded tyres and the use of sand/salt as anti-skid treatment a time varying emission model is needed. An empirical model accounting for these Nordic conditions was previously developed in Sweden. (2) For other roads with a less pronounced seasonal variation (e.g. in Denmark, Germany, Austria) methods using a constant emission factor maybe appropriate. Two models are presented here. Further, we apply the different emission models to data sets outside the original countries. For example, we apply the "Swedish" model for two streets without studded tyre usage and the "German", model for Nordic data sets. The "Swedish" empirical model performs best for streets with studded tyre use, but was not able to improve the correlation versus measurements in comparison to using constant emission factors for the Danish side. The "German" method performed well for the streets without clear seasonal variation and reproduces the summer conditions for streets with pronounced seasonal variation. However, the seasonal variation of PM emission factors can be important even for countries not using studded tyres, e.g. in areas with cold weather and snow events using sand and de-icing materials. Here a constant emission factor probably will under-estimate the 90-percentiles and therefore a time varying emission model need to be used or developed for such areas. All emission factor models consistently indicate that a large part (about 50-85% depending on the location) of the total PM10 emissions originates from non-exhaust emissions. This implies that reduction measures for the exhaust part of the vehicle emissions will only have a limited effect on ambient PM10 levels. (C) 2007 Elsevier Ltd. All rights reserved.

  • 188.
    Kindbom, Karin
    et al.
    IVL Swedish Environmental Research Institute.
    Sjöberg, Karin
    IVL Swedish Environmental Research Institute.
    Munthe, John
    IVL Swedish Environmental Research Institute.
    Peterson, Kjell
    IVL Swedish Environmental Research Institute.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Roos, Elisabet
    SMHI.
    Bergström, Robert
    SMHI, Research Department, Air quality.
    Nationell miljöövervakning av luft- och nederbördskemi 1996: IVL Rapport B 12891998Report (Other academic)
    Abstract [sv]

    I föreliggande rapport redovisas resultat från 1996 års mätningar av luftens och nederbördens sammansättning i bakgrundsmiljö i Sverige. Rapporten redovisar mätresultat från de båda nationella övervakningsnäten EMEP-nätet och Luft- och nederbördskemiska nätet. I rapporten redovisas även de spridnings- och depositionberäkningar som gjorts med Sverigemodellen. Samtliga mätningar drivs av IVL medan modellberäkningarna med Sverigemodellen utförs av SMHI. Verksamheten finansieras av Miljöövervakningsenheten vid Naturvårdsverket.

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  • 189.
    Kindbom, Karin
    et al.
    IVL Svenska Miljöinstitutet AB.
    Svensson, Annika
    IVL Svenska Miljöinstitutet AB.
    Sjöberg, Karin
    IVL Svenska Miljöinstitutet AB.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Nationell miljöövervakning av luft- och nederbördskemi 1997, 1998 och 19992001Report (Other academic)
    Abstract [en]

    Measurements of the composition of air and precipitation in background areas in Sweden during 1997, 1998 and 1999 are presented in the report. Results from two national networks, EMEP and the Swedish Precipitation Chemistry Network, both run by IVL Swedish Environmental Research Institute, are compiled and evaluated. Included in the presentation are also model calculations of dispersion and deposition of sulphur- and nitrogen compounds over Sweden. The modelling is based on monitoring results from 1997 and the calculations have been made using the MATCH-Sweden modelling system developed by SMHI, Swedish Meteorological and Hydrological Institute. The Swedish Environmental Protection Agency finances the activities. The monitoring programmes during the three years have included daily sampling of sulphur dioxide, nitrogen dioxide and particle bound sulphate in air at six stations 1997 and five stations 1998 and 1999. Daily measurements of soot, total-nitrate and total-ammonium have been performed at four stations. Monthly sampling of sulphur dioxide and nitrogen dioxide has been made at 12 stations 1997 and 1998 and at 13 stations 1999. Ozone concentrations in ground-level air have been monitored at six stations. Measurements of mercury in air have been performed at two stations regarding total gaseous mercury (TGM) and particle bound mercury. The measurements of sulphur and nitrogen compounds in air displayed a decreasing gradient from south to north. Generally, the higher concentrations of sulphur dioxide, sulphate, soot and nitrogen dioxide are found during winter, while high levels of ozone are registered during spring or early summer. The remaining compounds show a more uniform concentration during the seasons. The annual averages were comparable to, or lower, than previous years. The highest annual average air concentration of ground-level ozone was, as previous years, registered in Esrange. Ozone levels above 180 μg/m3 were not registered during the period. AOT40 values were on a comparable level with previous years, except for southern Sweden 1998 where AOT40 values were unusually low. Daily sampling of precipitation using a wet-only sampler has been made at one station and weekly sampling at three stations. At nearly 30 stations, monthly sampling using bulk-samplers was carried out. The precipitation samples were analysed with respect to pH, sulphate, nitrate, ammonium, chloride, calcium, magnesium, sodium and potassium. At four stations sampling of precipitation for analysis of heavy metals, total-mercury and methyl-mercury was made. The components in precipitation generally showed a decreasing gradient from south to north. The concentration of sulphate has decreased somewhat compared to previous years. The annual averages of pH showed higher values in northern Sweden than in the south. The pH values were slightly higher throughout the country than in earlier years. The concentrations in precipitation and the deposition of heavy metals and mercury generally showed lower values in northern and higher values in southern Sweden. The MATCH-Sweden model is a three-dimensional Eulerian atmospheric dispersion model, which is used for calculation of dispersion and deposition of air pollutants over Sweden. This model system also includes a method for data assimilation of measured concentrations in air and precipitation. In this report only some few examples of calculated annual mean concentrations and annual deposition maps for 1997 and 1998 are presented for sulphur, oxidised and reduced nitrogen. The MATCH-Sweden model has also been used to estimate air pollution budgets for Sweden for the years 1997 and 1998. The Swedish net import of air pollutants is substantial for sulphur and NHx-nitrogen. The Swedish contribution to deposition over Sweden is about 7 % for sulphur, 11 % for NOx-nitrogen and 20 % for NHxnitrogen. MATCH-Sweden results show somewhat larger deposition values than the EMEP model over Sweden for sulphur and NOx-nitrogen. For NHx-nitrogen the values are much larger, especially in Northern Sweden where the MATCH-Sweden values are 2-3 times larger than the EMEP model.

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  • 190.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Holmen, K
    Eneroth, K
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Summertime Siberian CO2 simulations with the regional transport model MATCH: a feasibility study of carbon uptake calculations from EUROSIB data2002In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 54, no 5, p. 834-849Article in journal (Refereed)
    Abstract [en]

    Biogenic surface fluxes Of CO2 over Europe and Siberia are implemented in the regional tracer transport model MATCH. A systematic comparison between simulated and observed CO2 fluxes and mixing ratios is performed for two observational sites in Russia taking into account both surface observations and vertical profiles of meteorological parameters and CO2 in the lowest 3 km from the summer months in 1998. We find that the model is able to represent meteorological parameters as temperature, humidity and planetary boundary layer height consistent with measurements. Further, it is found that the simulated surface CO2 fluxes capture a large part of the observed variability on a diurnal time scale. On a synoptic time scale the agreement between observations and simulation is poorer which leads to a disagreement between time series of observed and simulated CO2 mixing ratios. However, the model is able to realistically simulate the vertical gradient in CO2 in the lowest few kilometres. The vertical variability is studied by means of trajectory analysis together with results from the MATCH model. This analysis clearly illustrates some problems in deducing CO2 fluxes from CO2 mixing ratios measured in single vertical profiles. Studies of the regional variability Of CO2 in the model domain show that there exists no ideal vertical level for detecting the terrestrial signal Of CO2 in the free troposphere. The strongest terrestrial signal is found in the boundary layer above the lowest few hundred metres. Nevertheless, this terrestrial signal is small, and during the simulated period it is not possible to detect relative variations in the surface fluxes smaller than 20%. We conclude that a regional flux cannot be determined from single ground stations or a few vertical profiles, mainly due to synoptic scale variability in transport and in CO2 surface fluxes.

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  • 191.
    Klein, Thomas
    et al.
    SMHI, Core Services.
    Bergström, Robert
    SMHI, Research Department, Air quality.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Parameterization of dry deposition in MATCH2002Report (Other academic)
    Abstract [en]

    The present report describes the calculation of dry deposition in the Multi scale Atmospheric Transport and Chemistry modeling system (MATCH) applied in environmental monitoring studies. For this type of applications dry deposition is parameterized by means of a resistance concept. Modeled dry deposition velocities for different surface types, a variety of meteorological conditions and several chemical species are presented. The deposition’s dependence on the individual partial resistances and their variation with the meteorological conditions are illustrated by means of time-series. The details of the resistance concept are discussed in a pedagogical way in order to both facilitate understanding and to point out different deposition paths.Sensitivity studies have been performed for the laminar sub-layer resistance of particles for which two different settings of resistance values are compared. The importance of SO2 and NO2 uptake by the stomata of plants and the deposition of SO2 to the external parts of plants have also been investigated by means of sensitivity studies. In addition, horizontal maps and monthly mean values of dry deposition velocities based on meteorological data for 1998 are presented.

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  • 192.
    Klein, Thomas
    et al.
    SMHI, Core Services.
    Karlsson, Per-Erik
    IVL Swedish Environmental Research Institute.
    Andersson, Stefan
    SMHI, Research Department, Air quality.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Sjöberg, Karin
    IVL Swedish Environmental Research Institute.
    Assessing and improving the Swedish forecast and information capabilities for ground-level ozone2011Report (Other academic)
    Abstract [en]

    This study aims to assess and improve the Swedish forecast and information capabilities for ground-level ozone concentrations in ambient air. The assessment is based on a set of archived results from the Swedish operational chemical transport model MATCH and Swedish in-situ measurements of ozone covering the period of May 2008 to November 2010. The evaluation comprises two major activities: The first activity is an analysis of the overall model performance using standard statistical metrics suitable for longer time series. The second evaluation activity comprises in-detail analyses of the specific ozone episodes occurring in Sweden during the study period. In addition, trajectory modelling is used to investigate the meteorological conditions and transport patterns associated with those episodes. The evaluation of the model results shows that the model scores well according to standard evaluation criteria and confirms results of other studies in that the model easily meets the data quality requirements of the EU air quality directive 2008/50/EC. However, from an operational forecasting and information perspective it would be desirable to further improve the prediction of, in particular, high-level ozone episodes. Two different activities in our study are dedicated to the task of improving the forecast and information capabilities: The first activity tests the usefulness of statistical postprocessing of model results using regression techniques. The tests show promising results although the model performance during high-level ozone episodes is not improved. A limitation of our study is the relatively small archive of model data available for calibration andevaluation. Adaptive post-processing methods have not been tested in our study. The second activity aimed to improve ozone forecasting is a high-resolution model run for the year 2010. The higher reso-lution run gives slightly better results than the coarser operational model, which can be attributed to a better resolution of the physiography and thus certain physical and chemical processes. In particular, high-resolution simulations provide a more realisticrepresentation of the spatial ozone variation which is desirable for environmental assessments with a longer time horizon. However, from the perspective of operational ozone forecasting the increase in resolution cannot correct systematic problems such as an under-prediction of ozone if the source of ozone is non-local and the long-range transboundary transport is not correctly described by the European-scale model used as boundaries. Other potential sources of error are incomplete or erroneous emissions, representativeness issues, oversimplifications in the model’s physical or chemical processes, lacking data assimilation and initialization and oversimplifiedboundary conditions. While several of these issues are already addressed in current initiatives such as the EU FP7-project MACC, it is clear that further work will be needed during the coming years. Further work should also be invested in a better exploitation of the international developments within MACC and in the establishment of operational high-resolution air quality forecasts for Sweden, using boundary values from European-scale forecasts provided by theMACC-ensemble of regional air quality models.

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  • 193.
    Klein, Thomas
    et al.
    SMHI, Core Services.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Frankenberg, Britt
    SMHI, Core Services.
    Svensson, J
    SMHI.
    Broman, Barry
    SMHI, Research Department, Climate research - Rossby Centre.
    Bennet, Cecilia
    SMHI, Research Department, Air quality.
    ECDS - a Swedish Research Infrastructure for the Open Sharing of Environment and Climate Data2013In: Data Science Journal, E-ISSN 1683-1470, no 12, p. 1-9Article in journal (Refereed)
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  • 194. Klingberg, J.
    et al.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Karlsson, P. E.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Pleijel, H.
    Declining ozone exposure of European vegetation under climate change and reduced precursor emissions2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 19, p. 5269-5283Article in journal (Refereed)
    Abstract [en]

    The impacts of changes in ozone precursor emissions as well as climate change on the future ozone exposure of the vegetation in Europe were investigated. The ozone exposure is expressed as AOT40 (Accumulated exposure Over a Threshold of 40 ppb O-3) as well as PODY (Phytotoxic Ozone Dose above a threshold Y). A new method is suggested to express how the length of the period during the year when coniferous and evergreen trees are sensitive to ozone might be affected by climate change. Ozone precursor emission changes from the RCP4.5 scenario were combined with climate simulations based on the IPCC SRES A1B scenario and used as input to the Eulerian Chemistry Transport Model MATCH from which projections of ozone concentrations were derived. The ozone exposure of vegetation over Europe expressed as AOT40 was projected to be substantially reduced between the periods 1990-2009 and 2040-2059 to levels which are well below critical levels used for vegetation in the EU directive 2008/50/EC as well as for crops and forests used in the LRTAP convention, despite that the future climate resulted in prolonged yearly ozone sensitive periods. The reduction in AOT40 was mainly driven by the emission reductions, not changes in the climate. For the toxicologically more relevant POD1 index the projected reductions were smaller, but still significant. The values for POD1 for the time period 2040-2059 were not projected to decrease to levels which are below critical levels for forest trees, represented by Norway spruce. This study shows that substantial reductions of ozone precursor emissions have the potential to strongly reduce the future risk for ozone effects on the European vegetation, even if concurrent climate change promotes ozone formation.

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  • 195. Klingberg, J.
    et al.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Uddling, J.
    Karlsson, P. E.
    Pleijel, H.
    Ozone risk for vegetation in the future climate of Europe based on stomatal ozone uptake calculations2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 174-187Article in journal (Refereed)
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  • 196. Klingberg, Jenny
    et al.
    Karlsson, Per Erik
    Andersson, Camilla
    SMHI, Research Department, Air quality.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Karlsson, Gunilla Pihl
    Pleijel, Hakan
    Observed annual surface ozone maxima and minima in northern and central Europe from 1990-2015-latitude dependence and temporal trends2019In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 24, p. 201-214Article in journal (Refereed)
    Abstract [en]

    Ground-level ozone is an air pollutant that, despite reductions in precursor emission in Europe, still represents a risk to vegetation and human health. This study is based on observations of ozone concentrations ([O-3]) from 25 European monitoring stations, north of the Alps within the EMEP network, during the 26-year period from 1990-2015. We analyzed the maximum and minimum hourly [O-3] as well as the seasonal cycle in relation to latitude. In addition, temporal trends were studied. The maximum [O-3] increased towards the south of the study area, while the yearly minimum of daytime mean increased towards the north. There was a strong correlation between the day of year when the maximum [O-3] occurred and latitude: the maximum [O-3] occurred earlier in the north. The maximum daytime [O-3] decreased at all stations while the minimum daytime [O-3] increased at most stations during the studied time period.

  • 197. Kovalets, Ivan V.
    et al.
    Asker, Christian
    SMHI, Research Department, Air quality.
    Khalchenkov, Alexander V.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Lavrova, Tatyana V.
    Atmospheric dispersion of radon around uranium mill tailings of the former Pridneprovsky Chemical Plant in Ukraine2017In: Journal of Environmental Radioactivity, ISSN 0265-931X, E-ISSN 1879-1700, Vol. 172, p. 173-190Article in journal (Refereed)
  • 198. Kovalets, Ivan V.
    et al.
    Robertson, Lennart
    SMHI, Research Department, Air quality.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Didkivska, Svitlana N.
    Ievdin, Ievgen A.
    Trybushnyi, Dmytro
    Calculation of the far range atmospheric transport of radionuclides after the Fukushima accident with the atmospheric dispersion model MATCH of the JRODOS system2014In: International Journal of Environment and Pollution, ISSN 0957-4352, E-ISSN 1741-5101, Vol. 54, no 2-4, p. 101-109Article in journal (Refereed)
    Abstract [en]

    The paper presents estimates of the far-range atmospheric dispersion of radionuclides after the accident at Fukushima Daiichi Nuclear Power Plant (NPP), obtained using the long-range atmospheric dispersion model MATCH. Software tools were developed to run MATCH in the EU nuclear emergency response system JRODOS using freely available numerical weather prediction (NWP) data of the Global Forecasting System (GFS) operated by the United States National Center of Environmental Prediction (NCEP). Comparisons are made of results with JRODOS/MATCH and a standalone MATCH operated by Swedish Meteorological and Hydrological Institute (SMHI) driven by the European Center for Medium-Range Weather Forecasts (ECMWF) NWP data.

  • 199. Krecl, Patricia
    et al.
    Cipoli, Yago Alonso
    Targino, Admir Creso
    Castro, Lizeth Bibiana
    Gidhagen, Lars
    SMHI, Research Department, Air quality.
    Malucelli, Francisco
    Wolf, Alyson
    Cyclists' exposure to air pollution under different traffic management strategies2020In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 723, article id 138043Article in journal (Refereed)
  • 200. Krecl, Patricia
    et al.
    Cipoli, Yago Alonso
    Targino, Admir Creso
    Toloto, Matheus de Oliveira
    Segersson, David
    SMHI, Research Department, Air quality.
    Parra, Alvaro
    Polezer, Gabriela
    Moreton Godoi, Ricardo Henrique
    Gidhagen, Lars
    SMHI, Research Department, Air quality.
    Modelling urban cyclists' exposure to black carbon particles using high spatiotemporal data: A statistical approach2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 679, p. 115-125Article in journal (Refereed)
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