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Sökning: L773:1352 2310 > (2010-2011)

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1.
  • Andersson, August, et al. (författare)
  • (14)C-Based source assessment of soot aerosols in Stockholm and the Swedish EMEP-Aspvreten regional background site
  • 2011
  • Ingår i: Atmospheric Environment. - 1352-2310. ; 45:1, s. 215-222
  • Tidskriftsartikel (refereegranskat)abstract
    • Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line (14)C quantification with the chemothermal oxidation method at 375 degrees C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass (f(biomass)) for fall and winter periods in the range of one-third to half. Large temporal variations in (14)C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The f(biomass) appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion. These results for the largest metropolitan area in Scandinavia combine with other recent (14)C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere.
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2.
  • Buccoliere, Riccardo, et al. (författare)
  • City breathability and its link to pollutant concentration distribution within urban-like geometries
  • 2010
  • Ingår i: Atmospheric Environment. - ELSEVIER. - 1352-2310. ; 44:15, s. 1894-1903
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper is devoted to the study of pollutant concentration distribution within urban-like geometries. By applying efficiency concepts originally developed for indoor environments, the term ventilation is used as a measure of city “breathability”. It can be applied to analyse pollutant removal within a city in operational contexts. This implies the evaluation of the bulk flow balance over the city and of the mean age of air. The influence of building packing density on flow and pollutant removal is, therefore, evaluated using those quantities. Idealized cities of regular cubical buildings were created with packing density ranging from 6.25% to 69% to represent configurations from urban sprawl to compact cities. The relative simplicity of these arrangements allowed us to apply the Computational Fluid Dynamics (CFD) flow and dispersion simulations using the standard k–<img src="http://www.sciencedirect.com/scidirimg/entities/25b.gif" /> turbulence model. Results show that city breathability within the urban canopy layer is strongly dependent from the building packing density. At the lower packing densities, the city responds to the wind as an agglomeration of obstacles, at larger densities (from about 44%) the city itself responds as a single obstacle. With the exception of the lowest packing density, airflow enters the array through lateral sides and leaves throughout the street top and flow out downstream. The air entering through lateral sides increases with increasing packing density.At the street top of the windward side of compact building configurations, a large upward flow is observed. This vertical transport reduces over short distance to turn into a downward flow further downstream of the building array. These findings suggest a practical way of identifying city breathability. Even though the application of these results to real scenarios require further analyses the paper illustrates a practical framework to be adopted in the assessment of the optimum neighbourhood building layout to minimize pollution levels.
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3.
  • Dutcher, Dabrina D., et al. (författare)
  • Emissions from soy biodiesel blends: A single particle perspective
  • 2011
  • Ingår i: Atmospheric Environment. - Elsevier Science Ltd. - 1352-2310. ; 45:20, s. 3406-3413
  • Tidskriftsartikel (refereegranskat)abstract
    • Biodiesel has recently reemerged as a common fuel. However, emissions from biodiesel combustion have been studied in much less detail than those from traditional petroleum-based diesel. In this experiment, emissions from the combustion of different fuel blends (BOO, B02, B20, B99, where the number after B indicates the percentage, by volume, of biodiesel in the fuel) in a VW TDi engine were analyzed by aerosol time-of-flight mass spectrometers (ATOFMS) for single-particle composition and vacuum aerodynamic size. The ATOFMS results show that the PAH molecular weight distribution is not significantly affected by the fuel composition, and that sulfates are reduced by increased biodiesel content. Octanedioic acid (a carbonyl species) is increased with increased biodiesel concentration. Clustering results from the single-particle spectra show that the particles fall in five main types by chemical composition. The aerodynamic size distribution of these individual clusters was also determined. These results also show that methods used to identify diesel particle emissions for source apportionment are not applicable when significant concentrations of biodiesel are used in fuels. (C) 2011 Elsevier Ltd. All rights reserved.
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4.
  • Grundström, Maria, 1979-, et al. (författare)
  • Urban NO2 and NO pollution in relation to the North Atlantic Oscillation NAO
  • 2011
  • Ingår i: Atmospheric Environment. - 1352-2310. ; 45:4, s. 883-888
  • Tidskriftsartikel (refereegranskat)abstract
    • The North Atlantic Oscillation (NAO), a measure of the strength of the zonal wind across the North Atlantic Ocean, strongly influences weather conditions in NW Europe, e.g. temperature, precipitation and wind, especially during winter. It was hypothesised that elevated concentrations of nitrogen oxides in Gothenburg would be enhanced during negative NAO index (NAOI) conditions, representing more anticyclonic weather situations and thus leading to limited air mixing in the urban atmosphere, than situations with NAOI > 0. Hourly wintertime (DecembereFebruary) concentrations (1997e2006) of NO2, NO, air pressure, temperature and wind direction from an urban rooftop (30mabove street level) in the centre of the City of Gothenburg were analysed in relation to NAOI. Air pressure, the average concentration of nitrogen oxides (NOx ¼ NO2 þ NO), as well as the fraction of hourly NO2 and NO concentrations exceeding 90 mg m_3 and the fraction of daily NO concentrations exceeding 60 mg m_3, were significantly and negatively related to NAOI. Air temperature was positively correlated with NAOI. Southerly and westerly winds were more common in months with positive NAOI, while easterly and northerly winds were overrepresented in months with negative NAOI. High pollution concentrations dominantly occurred in situations with northerly and easterly wind directions. High NO2 and NO concentrations were associated with negative NAOI, especially in the morning when the traffic rush coincided with restricted air mixing. Over the tenyear period there were trends for more negative NAOI and increased time fractions with hourly NO2 concentrations exceeding 90 mgm_3. The conclusion of this study is that a climate shift towards higher or lower NAOI has the potential to significantly influence urban air pollution in North-West Europe, and thus the possibility to reach air quality standards, even if emissions remain constant.
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5.
  • Jeppsson, Knut-Håkan, et al. (författare)
  • Effects of animal activity and air temperature on methane and ammonia emissions from a naturally ventilated building for dairy cows
  • 2011
  • Ingår i: Atmospheric Environment. - 1352-2310. ; 45:37, s. 6760-6768
  • Tidskriftsartikel (refereegranskat)abstract
    • Knowledge of how different factors affect gas emissions from animal buildings can be useful for emission prediction purposes and for the improvement of emission abatement techniques. In this study, the effects of dairy cow activity and indoor air temperature on gas emissions were examined. The concentrations of CH(4), NH(3), CO(2) and N(2)O inside and outside a dairy cow building were measured continuously between February and May together with animal activity and air temperature. The building was naturally ventilated and had a solid concrete floor which sloped towards a central urine gutter. Manure was scraped from the floor once every hour in the daytime and once every second hour at night into a partly covered indoor pit which was emptied daily at 6 a.m. and at 5 p.m. Gas emissions were calculated from the measured gas concentrations and ventilation rates estimated by the CO(2) balance method. The animal activity and emission rates of CH(4) and NH(3) showed significant diurnal variations with two peaks which were probably related to the feeding routine. On an average day, CH(4) emissions ranged from 7 to 15 g LU(-1) h(-1) and NH(3) emissions ranged from 0.4 to 1.5 g LU(-1) h(-1) (1 LU = 500 kg animal weight). Mean emissions of CH(4) and NH(3) were 10.8 g LU(-1) h(-1) and 0.81 g LU(-1) h(-1), respectively. The NH(3) emissions were comparable to emissions from tied stall buildings and represented a 4% loss in manure nitrogen. At moderate levels, temperature seems to affect the behaviour of dairy cows and in this study where the daily indoor air temperature ranged from about 5 up to about 20 degrees C, the daily activity of the cows decreased with increasing indoor air temperature (r = -0.78). Results suggest that enteric fermentation is the main source of CH(4) emissions from systems of the type in this study, while NH(3) is mainly emitted from the manure. Daily CH(4) emissions increased significantly with the activity of the cows (r = 0.61) while daily NH(3) emissions increased significantly with the indoor air temperatures (r = 0.66). Daily CH(4) emissions were negatively correlated to the indoor air temperature (r = -0.84). This suggests that increased daily indoor air temperatures due to seasonal changes may bring about decreased animal activity which may decrease the release of CH(4) from dairy cows. Finally, changes in daily NH(3) emissions were influenced more by the indoor air temperature than by the activity of the cows. (C) 2011 Elsevier Ltd. All rights reserved.
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6.
  • King, M D, et al. (författare)
  • Interaction of nitrogen dioxide (NO2) with a monolayer of oleic acid at the air-water interface - A simple proxy for atmospheric aerosol
  • 2010
  • Ingår i: Atmospheric Environment. - 1352-2310. ; 44:14, s. 1822-1825
  • Tidskriftsartikel (refereegranskat)abstract
    • The reactions between atmospheric oxidants and organic amphiphiles at the air water interface of an aerosol droplet may affect the size and critical supersaturation required for cloud droplet formation. We demonstrate that no reaction occurs between gaseous nitrogen dioxide (1000 ppm in air) and a monolayer of an insoluble amphiphile, oleic acid (cis-9-octadecenoic acid), at the air water interface which removes material from the air water interface. We present evidence that the NO2 isomerises the cis-9-octadecenoic (oleic) acid to trans-9-octadecenoic (elaidic) acid. The study presented here is important for future and previous studies of (1) the reaction between the nitrate radical, NO3, and thin organic films as NO2 is usually present in high concentrations in these experimental systems and (2) the effect of NO2 air pollution on the unsaturated fatty acids and lipids found at the air liquid surface of human lung lining fluid.
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9.
  • Lindgren, Magnus, et al. (författare)
  • Analysis of unregulated emissions from an off-road diesel engine during realistic work operations
  • 2011
  • Ingår i: Atmospheric Environment. - 1352-2310. ; 45:30, s. 5394-5398
  • Tidskriftsartikel (refereegranskat)abstract
    • Emissions from vehicle diesel engines constitute a considerable share of anthropogenic emissions of pollutants, including many non-regulated compounds such as aromatic hydrocarbons and alkenes. One way to reduce these emissions might be to use fuels with low concentrations of aromatic hydrocarbons, such as Fischer&ndash;Tropsch (F&ndash;T) diesels. Therefore this study compared Swedish Environmental Class 1 diesel (EC1) with the F&ndash;T diesel fuel Ecopar&trade; in terms of emissions under varied conditions (steady state, controlled transients and realistic work operations) in order to identify factors influencing emissions in actual operation. Using F&ndash;T diesel reduced emissions of aromatic hydrocarbons, but not alkenes. Emissions were equally dependent on work operation character (load, engine speed, occurrence of transients) for both fuels. There were indications that the emissions originated from unburnt fuel, rather than from combustion products
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