| 1. |
- Ahlm, Lars, et al.
(författare)
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Particle number concentrations over Europe in 2030 : the role of emissions and new particle formation
- 2013
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus GmbH. - 1680-7367 .- 1680-7375 .- 1680-7324. ; 13:20, s. 10271-10283
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Tidskriftsartikel (refereegranskat)abstract
- The aerosol particle number concentration is a key parameter when estimating impacts of aerosol particles on climate and human health. We use a three-dimensional chemical transport model with detailed microphysics, PMCAMx-UF, to simulate particle number concentrations over Europe in the year 2030, by applying emission scenarios for trace gases and primary aerosols. The scenarios are based on expected changes in anthropogenic emissions of sulfur dioxide, ammonia, nitrogen oxides, and primary aerosol particles with a diameter less than 2.5 mu m (PM2.5) focusing on a photochemically active period, and the implications for other seasons are discussed. For the baseline scenario, which represents a best estimate of the evolution of anthropogenic emissions in Europe, PMCAMx-UF predicts that the total particle number concentration (N-tot) will decrease by 30-70% between 2008 and 2030. The number concentration of particles larger than 100 nm (N-100), a proxy for cloud condensation nuclei (CCN) concentration, is predicted to decrease by 40-70% during the same period. The predicted decrease in N-tot is mainly a result of reduced new particle formation due to the expected reduction in SO2 emissions, whereas the predicted decrease in N-100 is a result of both decreasing condensational growth and reduced primary aerosol emissions. For larger emission reductions, PMCAMx-UF predicts reductions of 60-80% in both N-tot and N-100 over Europe. Sensitivity tests reveal that a reduction in SO2 emissions is far more efficient than any other emission reduction investigated, in reducing N-tot. For N-100, emission reductions of both SO2 and PM2.5 contribute significantly to the reduced concentration, even though SO2 plays the dominant role once more. The impact of SO2 for both new particle formation and growth over Europe may be expected to be somewhat higher during the simulated period with high photochemical activity than during times of the year with less incoming solar radiation. The predicted reductions in both N-tot and N-100 between 2008 and 2030 in this study will likely reduce both the aerosol direct and indirect effects, and limit the damaging effects of aerosol particles on human health in Europe
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| 2. |
- Bidleman, Terry F., et al.
(författare)
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Biannual cycles of organochlorine pesticide enantiomers in arctic air suggest changing sources and pathways
- 2014
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus GmbH. - 1680-7367 .- 1680-7375. ; 14:17, s. 25027-25050
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Tidskriftsartikel (refereegranskat)abstract
- Air samples collected during 1994–2000 at the Canadian arctic air monitoring stationAlert (82300 N, 62200 W) were analyzed by enantiospecific gas chromatography –mass spectrometry for -hexachlorocyclohexane (-HCH), trans-chlordane (TC) and5 cis-chlordane (CC). Results were expressed as enantiomer fractions (EF = quantitiesof (+)/[(+)+(−)] enantiomers), where EFs=0.5, < 0.5 and > 0.5 indicate racemic composition,and preferential depletion of (+) and (−) enantiomers, respectively. Long-termaverage EFs were close to racemic values for -HCH (0.504±0.004, n =197) andCC (0.505±0.004, n =162), and deviated farther from racemic for TC (0.470±0.013,10 n =165). Digital filtration analysis revealed biannual cycles of lower -HCH EFs insummer-fall and higher EFs in winter-spring. These cycles suggest volatilization ofpartially degraded -HCH with EF < 0.5 from open water and advection to Alert duringthe warm season, and background transport of -HCH with EF> 0.5 during the coldseason. The contribution of sea-volatilized -HCH was only 11% at Alert, vs. 32%15 at Resolute Bay (74.68 N, 94.90W) in 1999. EFs of TC also followed biannual cyclesof lower and higher values in the warm and cold seasons. These were in phasewith low and high cycles of the TC/CC ratio (expressed as FTC =TC/(TC+CC)), whichsuggests greater contribution of microbially “weathered” TC in summer-fall vs. winterspring.CC was closer to racemic than TC and displayed seasonal cycles only in 1997–20 1998. EF profiles are likely to change with rising contribution of secondary emissionsources, weathering of residues in the environment, and loss of ice cover in the Arctic.Enantiomer-specific analysis could provide added forensic capability to air monitoringprograms.
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| 3. |
- Eliasson, Salomon, et al.
(författare)
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Assessing modelled spatial distributions of ice water path using satellite data
- 2010
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus GmbH. - 1680-7367 .- 1680-7375. ; 10:5, s. 12185-12224
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Tidskriftsartikel (refereegranskat)abstract
- The climate models used in the IPCC AR4 show large differences in monthly mean cloud ice. The most valuable source of information that can be used to potentially constrain the models is global satellite data. For this, the data sets must be long enough to capture the inter-annual variability of Ice Water Path (IWP). PATMOS-x was used together with ISCCP for the annual cycle evaluation in Fig. 7 while ECHAM-5 was used for the correlation with other models in Table 3. A clear distinction between ice categories in satellite retrievals, as desired from a model point of view, is currently impossible. However, long-term satellite data sets may still be used to indicate the climatology of IWP spatial distribution. We evaluated satellite data sets from CloudSat, PATMOS-x, ISCCP, MODIS and MSPPS in terms of monthly mean IWP, to determine which data sets can be used to evaluate the climate models. IWP data from CloudSat cloud profiling radar provides the most advanced data set on clouds. As CloudSat data are too short to evaluate the model data directly, it was mainly used here to evaluate IWP from the other satellite data sets. ISCCP and MSPPS were shown to have comparatively low IWP values. ISCCP shows particularly low values in the tropics, while MSPPS has particularly low values outside the tropics. MODIS and PATMOS-x were in closest agreement with CloudSat in terms of magnitude and spatial distribution, with MODIS being the best of the two. As PATMOS-x extends over more than 25 years and is in fairly close agreement with CloudSat, it was chosen as the reference data set for the model evaluation. In general there are large discrepancies between the individual climate models, and all of the models show problems in reproducing the observed spatial distribution of cloud-ice. Comparisons consistently showed that ECHAM-5 is the GCM from IPCC AR4 closest to satellite observations
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| 4. |
- Emanuelsson, Eva U., et al.
(författare)
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Formation of anthropogenic secondary organic aerosol (SOA) and its influence on biogenic SOA properties
- 2012
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus Publications. - 1680-7367 .- 1680-7375. ; 12:8, s. 20311-20350
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Tidskriftsartikel (refereegranskat)abstract
- Secondary organic aerosol (SOA) formation from mixed anthropogenic and biogenic precursors has been studied exposing reaction mixtures to natural sunlight in the SAPHIR chamber in Jülich, Germany. Several experiments with exclusively anthro- 5 pogenic precursors were performed to establish a relationship between yield and organic aerosol mass loading for the atmospheric relevant range of aerosol loads of 0.01 to 10 μgm−3. The yields (0.5–9 %) were comparable to previous data and further used for the detailed evaluation of the mixed biogenic and anthropogenic experiments. For the mixed experiments a number of different oxidation schemes were addressed. The 10 reactivity, the sequence of addition, and the amount of the precursors influenced the SOA properties. Monoterpene oxidation products, including carboxylic acids and dimer esters were identified in the aged aerosol at levels comparable to ambient air. OH radicals were measured by Laser Induced Fluorescence, which allowed for establishing relations of aerosol properties and composition to the experimental OH dose. Further 15 more, the OH measurements in combination with the derived yields for anthropogenic SOA enabled application of a simplified model to calculate the chemical turnover of the anthropogenic precursor and corresponding anthropogenic contribution to the mixed aerosol. The estimated anthropogenic contributions were ranging from small (8 %) up to significant fraction (>50 %) providing a suitable range to study the effect of aerosol 20 composition on the aerosol volatility (volume fraction remaining at 343 K: 0.86–0.94). The anthropogenic aerosol had higher oxygen to carbon ratio O/C and was less volatile than the biogenic fraction. However, in order to produce significant amount of anthropogenic SOA the reaction mixtures needed a higher OH dose that also increased O/C and provided a less volatile aerosol. A strong positive correlation was found between 25 changes in volatility and O/C with the exception during dark hours where the SOA volatility decreased while O/C did not change significantly. This change in volatility under dark conditions is likely due to chemical or morphological changes not affecting O/C.
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| 5. |
- Hede, Thomas, et al.
(författare)
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HULIS in Nanoaerosol Clusters; Investigations of Surface Tension and Aggregate Formation using Molecular Dynamics Simulations
- 2011
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus GmbH. - 1680-7367 .- 1680-7375.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Cloud condensation nuclei act as cores for water vapor condensation, and their composition and chemical properties may enhance or depress the ability for droplet growth. In this study we use molecular dynamics simulations to show that humic-like substances of larger systems (8.6 nm in diameter) mimic experimental data well referring to reduction of surface tension. The structural properties examined show the ability for the humic-like substances to aggregate inside the nanoaerosol clusters.
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| 6. |
- Nordin, E. Z., et al.
(författare)
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Secondary organic aerosol formation from gasoline passenger vehicle emissions investigated in a smog chamber
- 2012
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus Publications. - 1680-7367 .- 1680-7375. ; 12:12, s. 31725-31765
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Tidskriftsartikel (refereegranskat)abstract
- Gasoline vehicles have elevated emissions of volatile organic compounds during cold starts and idling and have recently been pointed out as potentially the main source of anthropogenic secondary organic aerosol (SOA) in megacities. However, there is a lack of laboratory studies to systematically investigate SOA formation in real-world exhaust. In this study, SOA formation from pure aromatic precursors, idling and cold start gasoline exhaust from one Euro II, one Euro III and one Euro IV passenger vehicles were investigated using photo-oxidation experiments in a 6 m3 smog chamber. The experiments were carried out at atmospherically relevant organic aerosol mass concentrations. The characterization methods included a high resolution aerosol mass spectrometer and a proton transfer mass spectrometer. It was found that gasoline exhaust readily forms SOA with a signature aerosol mass spectrum similar to the oxidized organic aerosol that commonly dominates the organic aerosol mass spectra downwind urban areas. After 4 h aging the formed SOA was 1–2 orders of magnitude higher than the Primary OA emissions. The SOA mass spectrum from a relevant mixture of traditional light aromatic precursors gave f43 (mass fraction at m/z = 4 3) approximately two times higher than to the gasoline SOA. However O : C and H : C ratios were similar for the two cases. Classical C6–C9 light aromatic precursors were responsible for up to 60% of the formed SOA, which is significantly higher than for diesel exhaust. Important candidates for additional precursors are higher order aromatic compounds such as C10, C11 light aromatics, naphthalene and methyl-naphthalenes.
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