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  • 1.
    Andersson, Camilla
    et al.
    SMHI, Research Department, Air quality.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Bergström, Robert
    SMHI, Research Department, Air quality.
    Interannual variation and trends in air pollution over Europe due to climate variability during 1958-2001 simulated with a regional CTM coupled to the ERA40 reanalysis2007In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 59, no 1, p. 77-98Article in journal (Refereed)
    Abstract [en]

    A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of surface ozone (O(3)), nitrogen dioxide (NO(2)) and particulate matter (PM) and its constituents over Europe during 1958-2001. The model was coupled to the meteorological reanalysis ERA40, produced at the European Centre for Medium-range Weather Forecasts. Emissions and boundary conditions of chemical compounds and PM were kept constant at present levels. The average European interannual variation, due to meteorological variability, ranges from 3% for O(3), 5% for NO(2), 9% for PM, 6-9% for dry deposition, to about 20% for wet deposition of sulphur and nitrogen. For the period 1979-2001 the trend in ozone, due to climate variability is increasing in central and southwestern Europe and decreasing in northeastern Europe, the trend in NO(2) is approximately opposite. The trend in PM is positive in eastern Europe. There are negative trends in wet deposition in southwestern and central Europe and positive trends in dry deposition overall. A bias in ERA40 precipitation could be partly responsible for the trends. The variation and trends need to be considered when interpreting measurements and designing measurement campaigns.

  • 2.
    Bennet, Cecilia
    et al.
    SMHI, Research Department, Air quality.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    A regional model for surface ozone in Southeast Asia2008In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, no 5, p. 718-728Article in journal (Refereed)
    Abstract [en]

    As part of the model intercomparison study MICS Asia II, the Swedish MATCH model was set up for Southeast and East Asia. In that study, the comprehensive photochemistry scheme of MATCH was used for the first time in Asia. The current work focuses on results of surface ozone from the MATCH model simulations falling outside the model intercomparison study. Model results of surface ozone concentrations for the entire year of 2001 were investigated and compared with measurements in Southeast Asia. The model produced higher surface ozone concentrations than the observations at all of the non-remote stations investigated but underestimated during the dry season at remote locations. Modelled seasonal variation was similar to, but less pronounced than, the variation in the measurements. This study indicates that NO(x) is the limiting precursor for ozone production in the model, while the fractionation in different species and total amount of non-methane volatile organic compounds (NMVOC) emissions are less important. Naturally emitted NMVOC, isoprene, is an important precursor of surface ozone at certain conditions, and a better inventory of these emissions is needed. Deposition velocities of ozone also have impact on surface concentrations. To improve the model performance, it is important to add a land use inventory with corresponding deposition velocities.

  • 3.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, Michael
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Omar, Ali H.
    The vertical distribution of thin features over the Arctic analysed from CALIPSO observations2011In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 1, p. 77-85Article in journal (Refereed)
    Abstract [en]

    Clouds play a crucial role in the Arctic climate system. Therefore, it is essential to accurately and reliably quantify and understand cloud properties over the Arctic. It is also important to monitor and attribute changes in Arctic clouds. Here, we exploit the capability of the CALIPSO-CALIOP instrument and provide comprehensive statistics of tropospheric thin clouds, otherwise extremely difficult to monitor from passive satellite sensors. We use 4 yr of data (June 2006-May 2010) over the circumpolar Arctic, here defined as 67-82 degrees N, and characterize probability density functions of cloud base and top heights, geometrical thickness and zonal distribution of such cloud layers, separately for water and ice phases, and discuss seasonal variability of these properties. When computed for the entire study area, probability density functions of cloud base and top heights and geometrical thickness peak at 200-400, 1000-2000 and 400-800 m, respectively, for thin water clouds, while for ice clouds they peak at 6-8, 7-9 and 400-1000 m, respectively. In general, liquid clouds were often identified below 2 km during all seasons, whereas ice clouds were sensed throughout the majority of the upper troposphere and also, but to a smaller extent, below 2 km for all seasons.

  • 4.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, Michael
    Omar, Ali H.
    The vertical distribution of thin features over the Arctic analysed from CALIPSO observations2011In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 1, p. 86-95Article in journal (Refereed)
    Abstract [en]

    Influx of aerosols from the mid-latitudes has a wide range of impacts on the Arctic atmosphere. In this study, the capability of the CALIPSO-CALIOP instrument to provide accurate observations of aerosol layers is exploited to characterize their vertical distribution, probability density functions (PDFs) of aerosol layer thickness, base and top heights, and optical depths over the Arctic for the 4-yr period from June 2006 to May 2010. It is shown that the bulk of aerosols, from about 65% in winter to 45% in summer, are confined below the lowermost kilometer of the troposphere. In the middle troposphere (3-5 km), spring and autumn seasons show slightly higher aerosol amounts compared to other two seasons. The relative vertical distribution of aerosols shows that clean continental aerosol is the largest contributor in all seasons except in summer, when layers of polluted continental aerosols are almost as large. In winter and spring, polluted continental aerosols are the second largest contributor to the total number of observed aerosol layers, whereas clean marine aerosol is the second largest contributor in summer and autumn. The PDFs of the geometrical thickness of the observed aerosol layers peak about 400-700 m. Polluted continental and smoke aerosols, which are associated with the intrusions from mid-latitudes, have much broader distributions of optical and geometrical thicknesses, suggesting that they appear more often optically thicker and higher up in the troposphere.

  • 5.
    Engardt, Magnuz
    et al.
    SMHI, Research Department, Air quality.
    Holmen, K
    Model simulations of anthropogenic-CO2 transport to an Arctic monitoring station during winter1999In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 51, no 2, p. 194-209Article in journal (Refereed)
    Abstract [en]

    We describe, and use, a limited area, 3-dimensional transport model. The model domain is located over the Arctic, but includes the majority of the anthropogenic CO2 emissions in western and eastern Europe, which together make up about 1/3 of the global CO2 emissions. The model is run for several winter periods, using anthropogenic CO2 emissions only, and the results are compared with independent CO2 measurements taken at a monitoring station on Spitsbergen in the high Arctic. We show that the initial concentrations and boundary values of the domain are not crucial for the results, and conclude that most of the measured variability above the winter baseline in CO2 at the Arctic monitoring station emanates from recent CO2 sources within the model domain. From the observed small spatial variability in the monthly mean atmospheric CO2 mixing ratio in the north Atlantic region, we assume that there is only little net exchange between the atmosphere and ocean during the studied periods. Based on the co-variation between CO2 and particulate mass,we hypothesise that most of the measured CO2 variability is due to anthropogenic fossil fuel emissions, although we can not rule out a biogenic CO2 component. Using the transport model, we compare different estimates of fossil-fuel consumption in the mid-latitudes. We find that the industrial centres and the surrounding gas-fields in the lower-Ob region (60 degrees-72 degrees N, 65 degrees-80 degrees E) occasionally have a much larger impact on the CO2 measurements at Spitsbergen than follows from a recent CO2 emission inventory. This implies that there may be an overlooked CO2 source in this region, possibly flaring of gas.

  • 6.
    Engardt, Magnuz
    et al.
    SMHI, Research Department, Air quality.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Simulations of future sulphur and nitrogen deposition over Europe using meteorological data from three regional climate projections2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, article id 20348Article in journal (Refereed)
    Abstract [en]

    We use a regional model of atmospheric chemistry and transport to investigate trends in sulphur and nitrogen deposition over Europe during the first half of the 21st century. To assess changes due to climate change, the model was operated with meteorology from a regional climate model simulating present and future climates. The sensitivity of the deposition calculations to uncertainties in the climate projections was explored by using output from three different climate models. Changes in anthropogenic air pollution emissions in Europe were extracted from the gridded RCP4.5 emission inventory. The modelling systems were evaluated by comparing average modelled precipitation, deposition and concentrations over a 20-year period with observations collected around the year 2000. We conclude that the deposition of sulphur and nitrogen containing species will mainly be governed by changes in European emissions of these species over the period 2000-2050. If future emissions follow the pathway of the RCP4.5 scenario, Europe can expect significantly lower deposition of sulphur and oxidised nitrogen in 2050 compared to 2000. For reduced nitrogen, large areas of western Europe will receive considerably more deposition in 2050 than in 2000, due to feedback of decreased sulphur concentrations on the atmospheric turnover time of reduced nitrogen. Domain averaged reductions of total deposition from 2000 to 2050 are 63, 41 and 0.9% for sulphur, oxidised-and reduced nitrogen, respectively. Climate change results in decreased wet deposition of sulphur and reduced nitrogen leading to increased atmospheric turnover time of these species. Climate and emission changes lead to decreased atmospheric turnover times of reduced nitrogen but increased atmospheric turnover times of sulphur and oxidised nitrogen. These relations are likely leading to altered source-receptor relations in the future.

  • 7.
    Engardt, Magnuz
    et al.
    SMHI, Research Department, Air quality.
    Simpson, David
    Schwikowski, Margit
    Granat, Lennart
    Deposition of sulphur and nitrogen in Europe 1900-2050. Model calculations and comparison to historical observations2017In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 69, article id 1328945Article in journal (Refereed)
  • 8.
    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.

  • 9.
    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.

  • 10.
    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.

  • 11. Leck, C
    et al.
    Heintzenberg, J
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    A meridional profile of the chemical composition of submicrometre particles over the East Atlantic Ocean: regional and hemispheric variabilities2002In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 54, no 4, p. 377-394Article in journal (Refereed)
    Abstract [en]

    Within the framework of SWEDARP (Swedish Antarctic Program) 92,93 an aerosol sampling program was carried out on board of M/S Palarbjorn which carried staff and material to the Nordic Antarctic Field exercises during the Austral summer 1992/1993. The cruise started 11 November 1992 from Oslo, went via Cape Town to Antarctica, and then back to Cape Town ,here the ship arrived on 4 January 1993. During the cruise, a meridional profile of physical and chemical submicrometre aerosol properties was derived covering the East Atlantic Ocean from 60degreesN to 70degreesS. The multicomponent aerosol data set combined with a trajectory analysis revealed a systematic meridional distribution of aerosol sources over the Atlantic that covered European and African continental Plumes and, South of 15degreesS, a largely biologically controlled marine aerosol. Median number concentrations calculated over the whole cruise spanned a factor of 20 between 2000 and 100 cm(-3), while total analyzed mass concentrations ranged between 7800 and 40 ng m(3). From the biologically dominated subset of the data in the southern hemisphere, relationships were developed that allowed an apportionment of the observed sulfate and ammonium concentration to biogenic and anthropogenic Sources over the whole meridional aerosol profile.

  • 12.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Exploiting the favourable alignment of CALIPSO's descending orbital tracks over Sweden to study aerosol characteristics2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, article id 21155Article in journal (Refereed)
    Abstract [en]

    One of the key knowledge gaps when estimating aerosol forcing and their role in air quality is our limited understanding of their vertical distribution. As an active lidar in space, the CALIOP-CALIPSO is helping to close this gap. The descending orbital track of CALIPSO follows elongated semi-major axis of Sweden, slicing its atmosphere every 2-3 d, thus providing a unique opportunity to characterise aerosols and their verticality in all seasons irrespective of solar conditions. This favourable orbital configuration of CALIPSO over Sweden is exploited in the present study. Using five years of night-time aerosol observations (2006-2011), we investigated the vertical distribution of aerosols. The role of temperature inversions and winds in governing this distribution is additionally investigated using collocated AIRS-Aqua and ERA-Interim Reanalysis data. It is found that the majority of aerosols (up to 70%) are located within 1 km above the surface in the lowermost troposphere, irrespective of the season. In summer, convection and stronger mixing lift aerosols to slightly higher levels, but their noticeable presence in the upper free troposphere is observed in the winter half of the year, when the boundary layer is decoupled due to strong temperature inversions separating local sources from the transport component. When southerly winds prevail, two or more aerosol layers are most frequent over southern Sweden and the polluted air masses have higher AOD values. The depolarisation ratio and integrated attenuated backscatter of these aerosol layers are also higher. About 30-50% of all aerosol layers are located below the level where temperature inversions peak. On the other hand, relatively cleaner conditions are observed when the winds have a northerly component.

  • 13.
    Wåhlstrom, Irene
    et al.
    SMHI, Research Department, Oceanography.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    A model sensitivity study for the sea-air exchange of methane in the Laptev Sea, Arctic Ocean2014In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 66, article id 24174Article in journal (Refereed)
    Abstract [en]

    The ocean's sinks and sources determine the concentration of methane in the water column and by that regulating the emission of methane to the atmosphere. In this study, we investigate how sensitive the sea-air exchange of methane is to increasing/decreasing sinks and sources as well as changes of different drivers with a time-dependent biogeochemical budget model for one of the shallow shelf sea in the Siberian Arctic, the Laptev Sea. The applied changes are: increased air temperature, river discharge, wind, atmospheric methane, concentration of nutrients in the river runoff or flux of methane from the sediment. Furthermore, simulations are performed to examine how the large range in observations for methane concentration in the Lena River as well as the rate of oxidation affects the net sea-air exchange. In addition, a simulation with five of these changes applied together was carried out to simulate expected climate change at the end of this century. The result indicates that none of the simulations changed the seawater to becoming a net sink for atmospheric methane and all simulations except three increased the outgassing to the atmosphere. The three exceptions were: doubling the atmospheric methane, decreasing the rivers' concentration of methane and increasing the oxidation rate where the latter is one of the key mechanisms controlling emission of methane to the atmosphere.

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