| 1. |
- Ohrlander, M., et al.
(författare)
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The effect of electron beam irradiation on PCL and PDXO-X monitored by luminescence and electron spin resonance measurements
- 2000
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:4, s. 1277-1286
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Tidskriftsartikel (refereegranskat)abstract
- The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(e-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and a tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(e-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.
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| 4. |
- Ketzel, M, et al.
(författare)
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Particle and trace gas emission factors under urban driving conditions in Copenhagen based on street and roof-level observations
- 2003
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Ingår i: Atmospheric Environment. - 1352-2310. ; 37:20, s. 2735-2749
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous measurements of particle size distribution (size/range 10-700 nm) inside an urban street canyon and a nearby urban background location in Copenhagen in May-November 2001 were used to separate the traffic source contribution in the street canyon from the background levels. The background concentrations are highly variable due to changing contributions from long-range transport and local sources showing a diurnal pattern with a shift to smaller particle sizes during midday hours. The average ratio background/street concentration is 0.26 for NOx and 0.35, 0.42, 0.60, 0.64, respectively, for CO, total particle number (ToN), surface and volume. The particle size distribution of the traffic source shows during daytime and evening hours (6-24) a maximum at particle sizes of 20-30 nm independent of the changing heavy-duty vehicle share during the same time interval. The particle number concentration highly correlated (R > 0.83) with NOx through a wide range of particle sizes. The method of inverse modelling was applied to estimate average fleet emission factors typical of urban conditions in Denmark. Emission factors per average vehicle were estimated as (2.8 +/- 0.5) x 10(14) particles/km, (1.3 +/- 0.2) g NOx/(veh km) and (11 +/- 2) g CO/(veh km). We observe two types of 'nanoparticle events' (a) in background, probably due to photochemistry and (b) in the night hours when traffic is dominated by diesel taxis. During night hours (0-5), the maximum in the emitted particle size distribution, is shifted to smaller sizes of about 15-18 nm. This shift to smaller particle sizes is related to an increase in the average NOx and ToN emission per vehicle by a factor of 2-3 and a reduced CO emission also by a factor of 2-3. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 5. |
- Ketzel, M, et al.
(författare)
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Particle size distribution and particle mass measurements at urban, near-city and rural level in the Copenhagen area and Southern Sweden
- 2004
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Ingår i: Atmospheric Chemistry and Physics. - 1680-7324. ; 4, s. 281-292
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Tidskriftsartikel (refereegranskat)abstract
- Particle size distribution (size-range 3-900 nm) and PM10 was measured simultaneously at an urban background station in Copenhagen, a near-city background and a rural location during a period in September-November 2002. The study investigates the contribution from urban versus regional sources of particle number and mass concentration. The total particle number (ToN) and NOx are well correlated at the urban and near-city level and show a distinct diurnal variation, indicating the common traffic source. The average ToN at the three stations differs by a factor of 3. The observed concentrations are 2500# cm(-3), 4500# cm(-3) and 7700# cm(-3) at rural, near-city and urban level, respectively. PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar concentration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations. Measures to reduce the local urban emissions of NOx and ToN are likely to affect both the street level and urban background concentrations, while for PM10 and ToV only measurable effects at the street level are probable. Taking into account the supposed stronger health effects of ultrafine particles reduction measures should address particle number emissions. The traffic source contributes strongest in the 10-200 nm particle size range. The maximum of the size distribution shifts from about 20-30 nm at kerbside to 50-60 nm at rural level. Particle formation events were observed in the 3-20 nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of preexisting aerosol particles. The maximum in the size distribution of the "traffic contribution" seems to be shifted to about 28 nm in the urban location compared to 22 nm at kerbside. Assuming NOx as an inert tracer on urban scale allows to estimate that ToN at urban level is reduced by 15-30% compared to kerbside. Particle removal processes, e. g. deposition and coagulation, which are most efficient for smallest particle sizes (<20 nm) and condensational growth are likely mechanisms for the loss of particle number and the shift in particle size.
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| 6. |
- Palmgren, Helena, 1955-, et al.
(författare)
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Salmonella in sub-Antarctica : low heterogeneity in salmonella serotypes in South Georgian seals and birds
- 2000
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Ingår i: Epidemiology and Infection. - : Cambridge University Press. - 0950-2688 .- 1469-4409. ; 125:2, s. 257-262
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Tidskriftsartikel (refereegranskat)abstract
- The number of human visitors to Antarctica is increasing rapidly, and with it a risk of introducing infectious organisms to native animals. To study the occurrence of salmonella serotypes in sub- Antarctic wildlife, faecal samples were collected from gentoo penguins, macaroni penguins, gray-headed albatrosses, black-browed albatrosses and Antarctic fur seals on Bird Island in the South Georgian archipelago during the austral summer of 1996 and 1998. In 1996, S. havana, S. typhimurium and S. enteritidis were isolated from 7% of gentoo penguins and 4% of fur seals. In 1998, however, 22% of fur seals were found to be infected with S. havana, S. enteritidis and S. newport. All isolates, except one, showed identical pulsed-field gel electrophoresis-patterns within each serotype, irrespective of sampling year and animal reservoir. No significant antibiotic resistance was found. The very low heterogeneity in the salmonella isolates found could either indicate a high genetic adaptation of the bacteria to the environment or a recent introduction of salmonella into the area.
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