| 1. |
- Acke, Filip, et al.
(författare)
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Study of the reduction and reoxidation of a CaO surface
- 1997
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Ingår i: J Phys Chem B. - 1520-5207 .- 1520-6106. ; 101:33, s. 6484-
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Tidskriftsartikel (refereegranskat)abstract
- The reduction of NO with CO and H2 is shown to comprise two basic reactions: a surface oxygen abstraction by the reducing agent and a reoxidation of the surface by NO. The former reaction step has been demonstrated by transient CO2 formation during CO exposure of oxidized CaO surfaces, while the latter was demonstrated by N2 and/or N2O transient formation during NO exposure of a prereduced CaO surface. It was shown that at low temperatures (between room temperature and 500 °C) both N2 and N2O were formed, but at temperatures above 500 °C only N2 was observed. The activation energies of the respective steps have been determined using temperature-programmed reaction experiments. The activation energy of the surface oxygen abstraction was determined to be 25 kcal/mol and is similar to the apparent activation energy of the overall reaction. The activation energy of the NO bond breakage was determined to be maximum 10 kcal/mol as measured by N2O formation. The importance of an N2O2- or N2O22- intermediate in the formation of N2O will be discussed, and the importance of N2O decomposition in forming N2 at temperatures above 500 °C will be compared with a N surface diffusion mechanism.
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| 2. |
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| 3. |
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| 4. |
- Gårdfeldt, Katarina, 1959, et al.
(författare)
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A kinetic study on the Abiotic Methylation of Divalent Mercury in the Aqueous phase
- 2003
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 304:1-3, s. 127-136
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism and kinetics of the formation of methylmercury from an experimental solution containing divalent mercury and acetic acid has been investigated. The experiments were performed in a 2-dm3 Teflon reactor. The organic mercury was measured with time resolutions varying between minutes and hours, after derivatisation, gas chromatography separation and Cold vapour atomic fluorescence detection. (GC)-CVAFS. CVAFS technique was used for determination of inorganic mercury in the aqueous phase using an automated mercury analyser. The experiments were carried out in concentrations relevant for natural waters. Our result shows that the reaction proceeds via mercury acetate complexes. A first order reaction coefficient has been calculated at various pH values, and was found to be (9.0±0.9)×10−7 s−1 at pH 3.6–3.7. The rate was not found to be enhanced by UV-light when taking into account the photolytical degradation of methylmercury. The reaction rate at various pH values, the influences of some other relevant reaction parameters, and implications for atmospheric and terrestrial waters are discussed.
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| 8. |
- Gårdfeldt, Katarina, 1959, et al.
(författare)
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Evasion of Mercury from coastal and open waters of the Atlantic ocean and the Mediterranean sea
- 2003
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Ingår i: Atmospheric Environment. - 1352-2310 .- 1873-2844. ; 37:Suppl 1
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved gaseous mercury (DGM) was measured in coastal Atlantic seawater and in the Mediterranean Sea. The Atlantic measurements were performed during September 1999 at the Mace Head Atmospheric Research Station, situated on the Irish west coast. The measurements in the Mediterranean Sea were made along a 6000 km cruise path from 14 July to 9 August 2000 in the framework of the Med-Oceanor project. Total gaseous mercury (TGM) concentrations in air were continuously measured with a 5 min time resolution using an automated mercury analyser (Tekran 2537A) during both expeditions. Paired TGM and DGM samples from all campaigns showed that the surface water was supersaturated with elemental mercury. The mercury evasion was estimated using a gas exchange model (J. Geophys. Res. 97 (1992) 7373), which uses salinity, wind speed and water temperature as independent parameters. The predicted average mercury evasion from the coastal Atlantic water was 2.7 ng m−2 h−1 implying that the concentration of TGM in the Atlantic air is enhanced by mercury evasion from the sea. Measurements in different regions of the Mediterranean Sea showed spatial variations in DGM concentrations. The highest DGM concentration (90 pg l−1) was observed at a location in the Strait of Sicily (37°16N 11°52E). The mercury evasion in the eastern sector of the Mediterranean Sea (area: 32–36°N, 17–28°E) was generally higher (7.9 ng m−2 h−1) than that observed in the Tyrrhenian Sea (4.2 ng m−2 h−1) or in the western sector (2.5 ng m−2 h−1) (areas: 38–42°N, 8–13°E and 38–41°N, 7–8°E, respectively). Estimations of mercury evasion were also made at Mediterranean coastal sites using a dynamic chamber technique. In addition, a newly developed method making continuous in situ DGM measurements possible was tested.
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| 9. |
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| 10. |
- Gårdfeldt, Katarina, 1959, et al.
(författare)
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Oxidation of atomic mercury by hydroxyl radicals and photoinduced decomposition of methylmercury species in the aqueous phase
- 2001
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Ingår i: Atmospheric Environment. - 1352-2310 .- 1873-2844. ; 35:17, s. 3039-3047
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Tidskriftsartikel (refereegranskat)abstract
- The rate constant for Hg0+.OH, kHg0+.OH=(2.4±0.3)×109 M−1 s−1, in the aqueous phase was determined using a relative rate technique with methyl mercury as reference compound. The .OH initiated mercury reaction proceeds via the molecular Hg(I) radical which is oxidised to Hg(II) by dissolved O2. The reaction can be of importance under certain atmospheric circumstances, such as when the aqueous phase capacity of forming OH radicals is significant and the gas phase concentration of ozone drops. The same end product, i.e. Hg(II) was observed from the photodegradation of methylmercury hydroxide. In this case, molecular Hg(I) radicals are again likely to be formed after photodegradation of the Hg–C bond with subsequent oxidation. A lifetime of 230 h of methylmercury at outdoor conditions was estimated due to this reaction. The action of .OH on methylmercury species also involves breaking of organometallic bonds and formation of Hg(II). Speciation of these reaction products from methylmercury is important for the estimation of biogeochemical cycling of mercury.
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| 11. |
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| 12. |
- Munthe, John, et al.
(författare)
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Distribution of atmospheric mercury species in Northern Europe: Final results from the MOE-project
- 2003
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Ingår i: Atmospheric Environment. - 1352-2310 .- 1873-2844. ; 37:Suppl 1
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Tidskriftsartikel (refereegranskat)abstract
- The mercury species over Europe (MOE) project was aimed at identifying sources, occurrence and atmospheric behaviour of atmospheric Hg species. Within MOE, emission measurements, ambient air measurements, process and regional-scale modelling and laboratory measurements were conducted. In this work, a summary of some of the main results is given. From the emission measurements, information on stack gas concentrations and emission factors for five coal fired power plants and three waste incinerators are presented. Results from field measurements of mercury species in ambient air at five locations in Northern Europe are presented. Examples from regional-scale atmospheric modelling are also given. The results emphasise the importance of information on Hg species for instance in emission inventories and measurement data from background sites. Furthermore, the importance of considering the role of the global cycling of mercury in future control strategies is emphasised
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| 13. |
- Snis, Anders, et al.
(författare)
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Abstraction of preadsorbed oxygen from CaO(100) by carbon monoxide
- 1994
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Ingår i: Surf Sci Lett. - 0039-6028. ; 310:1-3
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism for abstraction of preadsorbed oxygen from CaO(100) by CO(g) to form CO2(g) is investigated by electronic structure calculations. The reaction mechanism is assumed to be the reverse of the one obtained for the decomposition of N2O(g) at CaO(100) [Surf. Sci 292 (1993) 317]. A 32 kcal/mol barrier for reaction is calculated. Adsorbed oxygen, Oads, to surface vibration frequencies in the range 840–930 cm−1 are calculated. These values are in qualitative agreement with experiment.
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| 14. |
- Snis, Anders, et al.
(författare)
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N2O adsorption and decomposition at a CaO (100) surface studied by means of theory
- 1993
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Ingår i: Surf Sci. - 0039-6028. ; 292:3, s. 317-324
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption and decomposition of an N2O molecule at different sites on a CaO(s) surface are investigated by means of ab initio quantum chemistry. The calcium, Ca2+, and oxygen, Os2−, sites at a perfect (100) surface and at a corner position, Oc2−, are considered. Adsorption energies at different sites are calculated and the largest value, 6 kcal/mol, is obtained for a corner site. The barrier for dissociation is calculated to 26 and 27 kcal/mol at the Oc2− and Os2− sites, respectively. These values are some 10 kcal/mol lower than the experimental estimate, and the discrepancy is understood from methodological difficulties to describe the free N2O molecule. A mechanism for the dissociation over an O2− site is proposed, whereby the transfer of the O atom goes via a linear N-N … O … O2− transition state.
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| 15. |
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| 16. |
- Sommar, Jonas, 1969, et al.
(författare)
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A kinetic study of the gas-phase reaction between the hydroxylradical and atomic mercury
- 2001
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Ingår i: Atmos.Environ. - 1352-2310 .- 1873-2844. ; 35:17, s. 3049-3054
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Tidskriftsartikel (refereegranskat)abstract
- The atom is the dominating species of mercury in the atmosphere. Its oxidation processes are of great interest since it is mainly oxidised mercury that undergoes deposition and thereby spreads into the ecosystems and becomes bioaccumulated. The kinetics of the gas-phase reaction between atomic mercury and hydroxyl radical has been determined at room temperature and atmospheric pressure of air by relative rate technique. OH radicals were produced by photolysis employing methyl nitrite. By using cyclohexane as the reference compound, the rate coefficient obtained was k(Hg0+·OH)=(8.7±2.8)×10−14 cm3 s−1 leading to natural lifetimes of mercury at global mean conditions of 4–7 month due to this reaction.
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| 17. |
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| 18. |
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| 19. |
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| 21. |
- Strömberg, Dan, 1959, et al.
(författare)
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Relativistic calculations on some mercury sulphide molecules
- 1991
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Ingår i: Water Air and Soil Poll. - 0049-6979. ; 56:1, s. 681-695
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Tidskriftsartikel (refereegranskat)abstract
- Relativistic quantum calculations at the CASSCF- and CCI-levels were performed on the Hg(SH)2, HgSH and HgS molecules. The relativistic effects were taken into account by a relativistic effective core potential method. Dissociation energies and optimal geometries were calculated for these three molecules, which are plausible atmospheric Hg compounds. The Hg(SH)2 and HgSH molecules (in the gaseous phase) have never been studied before, neither experimentally nor theoretically, i.e. the existence of these molecules are uncertain. The theoretical dissociation energies, De's, of Hg(SH)2 and HgSH (at the CCI-level) were 59 kcal·mol–1 and 3 kcal·mol–1, respectively, indicating that Hg(SH)2 could be stable in the atmosphere but probably not HgSH. The theoretical De of HgS differs very much from the experimental one, but the reason for this is not clear. The Hg-S distances for Hg(SH)2, HgSH and HgS were found to be 2.38, 2.63 and 2.30 Å, respectively. The Hg-S-H angle in Hg(SH)2 was optimized to 93°. The excitation energies of Hg(SH)2, Hg(SH)2(H2O)4 and (HSHg)2S were calculated in order to see whether these species can absorb photons with wavelengths longer than 290 nm (the sunlight limit) and subsequently be photolyzed. The Hg(SH)2(H2O)4 complex is intended as a model for Hg(SH)2(aq). Photoreduction of Hg-sulfide species in sea water, yielding Hg0, could be an important source of Hg in the atmosphere. Excitation energies lower than the sunlight limit (4.3 eV290 nm) were found for Hg(SH)2 and Hg(SH)2(H2O)4, although the lowest spin and dipole allowed excitations probably lie slightly (0.2 to 0.3 eV) above this limit. Therefore a photodecomposition of Hg(SH)2(g) and Hg(SH)2(aq) by sunlight seems likely to occur.
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| 23. |
- Ahlbäck, Anders, 1977, et al.
(författare)
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Electricity from Renewable Energy Sources - POPA CTDA : Policy pathways to promote the development and adoption of cleaner technologies
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Executive summary Introduction In the strive towards a sustainable society, environmental technologies will play an increasingly important role. This has been acknowledged by the European Commission, and through the launching of the rather ambitious Environmental Technologies Action Plan (ETAP) the Commission has committed to the wide-spread of clean technologies in all the sectors of society. This programme encourage a numerous of actions designed to “remove barriers for the development and diffusion of environmental technologies”, to “ensure that the EU will take a leading role in developing and applying such technologies”, and to “mobilise all stakeholders in support of these objectives” (EU, 2004a). As a measure within the framework of ETAP, this project is designed to identify policy pathways to the promotion and development of clean technology development (POPA-CTDA) in the sectors of industry, transport, agriculture and energy. This case study deals with renewable energy technologies (RET) (bio-fuelled combined heat and power, wind power and solar power). Currently driven by all three pillars of sustainability in addition to the ‘traditional’ environmental one, RETs are increasingly looked upon as commercially competitive alternative to fossil based energy technologies. Use of renewable energy is growing on the global market - not only in niche applications as e.g. remote installations but on the broader energy/electricity markets as well. The share of renewable energy in the global primary energy supply (TPES) is about 11.3%, which of the vast majority is combustible bio resources (about 10.8%) and about 0.5% being wind, solar and geothermal (IEA, 2005). On the European energy market, RETs accounts for approximately 5% of TPES. This can be compared with the 12% penetration target by 2010 stated by the Commission in 1997. Methodological approach Starting point for the design of an integrated policy strategy supporting the development and adoption of RETs are the barriers and drivers responsible for the corresponding engagement of relevant actors in this field. Both barriers and drivers have been identified in a previous study, Work Package 2 (WP2), by the means of a behavioural approach developed by Montalvo (2001; 2002) on the basis of a survey conducted with actual and potential developers, manufacturers, operators and end-users of RETs from Austria, Germany, Netherlands, UK, Sweden and Hungary. In the survey actors in the energy UGOT POPA-CTDA: Work package 3 5 sector where asked about their opinions concerning development and adoption of RETs. Various aspects of their attitudes where addressed such as economic and environmental risk perception, relevant pressure arising from the social environment, the market and regulatory bodies and of their own technical and managing capabilities. The full analysis of the questionnaire is presented in the WP2 report. In the present study, Work Package 3, plausible policy instruments are identified to address those barriers found in WP2 and to encourage the diffusion of RETs. The insights presented in this report are based on literature study, interviews and the questionnaire study conducted in WP2. Main insights Economy Costs of producing electricity from RETs have been greatly reduced during latest decades but are generally still above the ones of fossil fuels; in particular PV technology that is, roughly, 10 times as expensive as average generation costs.1 The inability to include environmental damage costs of electricity generation (combustion of fossil fuels, nuclear power plants or even renewable technologies), the vast amount of direct or indirect subsidies, tax concessions etc. all distort competition on the energy market. Hence, some level of economic support is required for RETs to compete on the open market. In the case of both wind and solar power, the German feed-in law has proved very successful in lowering investment risk and encouraging new installations. Market On a local level, the job and economic growth opportunities derived from an establishment of local electricity production is becoming increasingly recognised. RETs compared with fossil based technologies are generally more labour intensive and, coupled with increasing recognition of RETs to fulfil national/local sustainability targets, provides an attractive option for politicians and entrepreneurs to promote local business. This is particularly a driver to establish biomass power and, if locally available, biomass resources via crop or forestry industry. 1 Average spot market price for electricity in the Eu-15 was in 2004 about 30-35 €/MWh, where average generation cost for PV is roughly 500 €/MWh electricity. UGOT POPA-CTDA: Work package 3 6 Technology and infrastructure Several interviewees pointed out performance, power output fluctuations (intermittency), actual power generation costs (factoring in costs of maintenance and service etc.) and lifetime as technological uncertainties and potential barriers to up-take. There is a need for further RD&D (research, development and demonstration) to develop both specific technology characteristic and systemic issues as grid compatibility. The varying power output of renewable generation and its consequences to power distribution is a source for controversy and may pose challenges in grid management. While it was earlier believed that even small fractions of intermittent capacity would cause instability on the power grid, new empirical data from practical examples2 shows that it is foremost a question of grid-management techniques. Institutional and regulative While wind power in general has gained in economic competitiveness, several interviewees mention regulative barriers as, perhaps, the main obstacle to a wide-spread diffusion. Issuing building permits is a complicated and time consuming process, where in Sweden, for example, several authorities at various levels are involved at different stages. A projector has to face the same process twice; first against the planning and building regulation, then the environmental legislation, in order to obtain building permits. Opposing groups may quite easily appeal and, thereby, delaying the process up to several years and risking the economy of a project. Especially small actors with no internal legal resources may face great challenges in the planning phase of a project. The coordination between the involved authorities is regarded as not very well-organised and there most definitely is a large potential to streamline the current processes. Recommendations Policy support on the EU level via communications, directives green/white papers etc. is a significant driver to policy implementation on the national level. It is of most importance to continuing to show this support by stating new targets for RET penetration (post-Kyoto objectives) and ensure compliance with e.g. national Kyoto-bindings. 2 E.g. in western Denmark, over 20% of the total load is covered by wind energy (IEA, 2005). UGOT POPA-CTDA: Work package 3 7 RETs in general • The European Emission Trading Scheme (ETS) has yet to prove its positive affects on RET diffusion. The potential is great however, but is to a large deal dependent on the size of the national allocation plans. If the acceptance and compliance of the scheme is not kept strong enough, the potential might very well get lost in a political barging between member states. • The formation of a single European electricity market have the potential of being the “hardware” necessary for implementing EU-wide supporting schemes. Particularly a common market for Tradable Green Certificates could be realised, where actors all over Europe would trade green electricity, ensuring a wide competition among producers and, thereby, keeping over all costs low. • RETs are in the need of continuing R&D support to increase product performance and lower manufacturing costs. Positive side-effects of R&D and demonstration programmes may be gained from actors forming networks and alliances for knowledge transfers and partnership. This is a necessity to counter powerful coalitions promoting fossil based technologies that for decades have influenced the institutional framework in favour of coal, oil and natural gas. • To minimise risk perception of investment, clear and long-term policy guidelines is needed to support RETs. Almost all interviewees expressed the short-term design of the current supporting schemes as a major barrier to investments. Some level of security is needed to induce investments, and that is foremost achieved by clearly stated rules and stable support. Biomass • Even though biomass is being close to commercially competitive, it is still in the need of economic support. The CHP technology in it self is well proven and developed; future technology developments will probably focus on the gasification of biomass resources, where there is extensive efficiency gains to be made in the production of electricity. UGOT POPA-CTDA: Work package 3 8 Wind Power • For wind power to be able to compete with old (often governmentally financed) installations, some level of economic support is still needed. Germany and Spain have primarily through the use of feed-in systems emerged as world leaders in the use of wind power in their national electricity systems. • Issuing building permit processes are often time consuming and perceived as unreasonably complicated. To counter this, there are needs to both streamline the permit process by coordinating involved governmental bodies and to pre-allocate land for wind power installations. • The intermittency of wind power generation might prove to have deteriorated affects on power quality in regions with relatively high shares of installations. This is mostly a matter of managing the power production/transfer with dedicated routines and technology, but will require R&D efforts to increase the knowledge of how
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