| 1. |
- Ahlm, Lars, 1976-, et al.
(författare)
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A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest
- 2010
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 10:6, s. 3063-3079
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Tidskriftsartikel (refereegranskat)abstract
- Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.
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| 2. |
- Ahlm, Lars, et al.
(författare)
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Emission and dry deposition of accumulation mode particles in the Amazon Basin
- 2010
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 10:21, s. 10237-10253
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Tidskriftsartikel (refereegranskat)abstract
- Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, pointed downward in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net emission fluxes dominated. However, in wind sectors associated with higher anthropogenic influence, net deposition fluxes dominated. The net emission fluxes were interpreted as primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and these emissions were best correlated with horizontal wind speed by the equation log10F=0.47·U+2.26 where F is the emission number flux of 0.5–2.5 μm particles [m−2s−1] and U is the horizontal wind speed [ms−1] at the top of the tower.
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| 3. |
- Delle, M., et al.
(författare)
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Celiac trunk coverage in endovascular aneurysm repair
- 2010
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Ingår i: Scandinavian Journal of Surgery. - : SAGE Publications. - 1457-4969. ; 99:4, s. 226-229
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND AIMS: This retrospective study was undertaken to examine the risks associated with obstruction of the coeliac trunk in the process of treating aneurysms with endografting. MATERIAL AND METHODS: 120 patients were treated by endografting for aneurysmal disease. Of these, a subgroup of 9 patients had their celiac trunk covered. If possible, a preoperative angiography was performed to evaluate collateral flow from the superior mesenteric artery. This was considered to predict the risk for ischemia. RESULTS: None of the patients had any severe clinical event of the celiac trunk occlusion or clinical signs of intestinal ischemia. Three patients had transient increase of liver enzymes. CONCLUSIONS: In cases where the distal landing zone of the descending thoracic aorta is to short for endografting, covering of the celiac trunk may be an option if no other surgical alter-native is apparent. Preoperative angiography to visualise the presence of collateral vessels from the superior mesenteric artery is recommended.
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| 4. |
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| 5. |
- Orlando, Ludovic, et al.
(författare)
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Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 499:7456, s. 74-
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Tidskriftsartikel (refereegranskat)abstract
- The rich fossil record of equids has made them a model for evolutionary processes(1). Here we present a 1.12-times coverage draft genome from a horse bone recovered from permafrost dated to approximately 560-780 thousand years before present (kyr BP)(2,3). Our data represent the oldest full genome sequence determined so far by almost an order of magnitude. For comparison, we sequenced the genome of a Late Pleistocene horse (43 kyr BP), and modern genomes of five domestic horse breeds (Equus ferus caballus), a Przewalski's horse (E. f. prze-walskii) and a donkey (E. asinus). Our analyses suggest that the Equus lineage giving rise to all contemporary horses, zebras and donkeys originated 4.0-4.5 million years before present (Myr BP), twice the conventionally accepted time to the most recent common ancestor of the genus Equus(4,5). We also find that horse population size fluctuated multiple times over the past 2 Myr, particularly during periods of severe climatic changes. We estimate that the Przewalski's and domestic horse populations diverged 38-72 kyr BP, and find no evidence of recent admixture between the domestic horse breeds and the Przewalski's horse investigated. This supports the contention that Przewalski's horses represent the last surviving wild horse population(6). We find similar levels of genetic variation among Przewalski's and domestic populations, indicating that the former are genetically viable and worthy of conservation efforts. We also find evidence for continuous selection on the immune system and olfaction throughout horse evolution. Finally, we identify 29 genomic regions among horse breeds that deviate from neutrality and show low levels of genetic variation compared to the Przewalski's horse. Such regions could correspond to loci selected early during domestication.
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| 6. |
- Vogt, Matthias, et al.
(författare)
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Heated submicron particle fluxes using an optical particle counter in urban environment
- 2013
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13:6, s. 3087-3096
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Tidskriftsartikel (refereegranskat)abstract
- From May 2008 to March 2009 aerosol emissions were measured using the eddy covariance method covering the size range 0.25 to 2.5 mu m diameter (D-p) from a 105m tower, in central Stockholm, Sweden. Supporting chemical aerosol data were collected at roof and street level. Results show that the inorganic fraction of sulfate, nitrate, ammonium and sea salt accounts for approximately 15% of the total aerosol mass < 1 mu m D-p (PM1) with water soluble soil contributing 11% and water insoluble soil 47%. Carbonaceous compounds were at the most 27% of PM1 mass. It was found that heating the air from the tower to 200 degrees C resulted in the loss of approximately 60% of the aerosol volume at 0.25 mu m D-p whereas only 40% of the aerosol volume was removed at 0.6 mu m D-p. Further heating to 300 degrees C caused very little additional losses < 0.6 mu m D-p. The chemical analysis did not include carbonaceous compounds, but based on the difference between the total mass concentration and the sum of the analyzed non-carbonaceous materials, it can be assumed that the non-volatile particulate material (heated to 300 degrees C) consists mainly of carbonaceous compounds, including elemental carbon. Furthermore, it was found that the nonvolatile particle fraction < 0.6 mu m D-p correlated (r(2) = 0.4) with the BC concentration at roof level in the city, supporting the assumption that the non-volatile material consists of carbonaceous compounds. The average diurnal cycles of the BC emissions from road traffic (as inferred from the ratio of the incremental concentrations of nitrogen oxides (NOx) and BC measured on a densely trafficked street) and the fluxes of non-volatile material at tower level are in close agreement, suggesting a traffic source of BC. We have estimated the emission factors (EFs) for non-volatile particles < 0.6 mu m D-p to be 2.4 +/- 1.4 mg veh(-1) km(-1) based on either CO2 fluxes or traffic activity data. Light (LDV) and heavy duty vehicle (HDV) EFs were estimated using multiple linear regression and reveal that for non-volatile particulate matter in the 0.25 to 0.6 mu m D-p range, the EFHDV is approximately twice as high as the EFLDV, the difference not being statistically significant.
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| 7. |
- Vogt, Matthias, et al.
(författare)
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Seasonal and diurnal cycles of 0.25–2.5 μm aerosol fluxes over urban Stockholm, Sweden
- 2011
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 63:5, s. 935-951
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Tidskriftsartikel (refereegranskat)abstract
- Size resolved aerosol and gas fluxes were measured in Stockholm from 1 April 2008 to 15 April 2009 over both urban and green sectors. CO2 and H2O fluxes peaked in daytime for all seasons. CO2 concentrations peaked in winter. Due to vegetation influence the CO2 fluxes had different diurnal cycles and magnitude in the two sectors. In the urban sector, CO2 fluxes indicated a net source. The sector dominated by residential areas and green spaces had its highest aerosol fluxes in winter. In spring, super micrometer concentrations for both sectors were significantly higher, as were the urban sector rush hour fluxes. The submicrometer aerosol fluxes had a similar diurnal pattern with daytime maxima for all seasons. This suggests that only the super micrometer aerosol emissions are dependent on season. During spring there was a clear difference in super micrometer fluxes between wet and dry streets. Our direct flux measurements have improved the understanding of the processes behind these aerosol emissions. They support the hypothesis that the spring peak in aerosol emissions are due to road dust, produced during the winter, but not released in large quantities until the roads dry up during spring, and explain why Stockholm has problems meeting the EU directive for aerosol mass (PM10).
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| 8. |
- Vogt, Matthias, et al.
(författare)
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The relationship between 0.25-2.5 mu m aerosol and CO2 emissions over a city
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:10, s. 4851-4859
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Tidskriftsartikel (refereegranskat)abstract
- Unlike exhaust emissions, non-exhaust traffic emissions are completely unregulated and in addition, there are large uncertainties in the non-exhaust emission factors required to estimate the emissions of these aerosols. This study provides the first published results of direct measurements of size resolved emission factors for particles in the size range 0.25-2.5 mu m using a new approach to derive aerosol emission factors based on carbon dioxide (CO2) emission fluxes. Aerosol fluxes were measured over one year using the eddy covariance method at the top of a 105m high communication tower in Stockholm, Sweden. Maximum CO2 and particle fluxes were found when the wind direction coincided with the area of densest traffic within the footprint area. Negative fluxes (uptake of CO2 and deposition of particles) coincided with periods of sampling from an urban forest area. The fluxes of CO2 were used to obtain emission factors for particles by assuming that the CO2 fluxes could be directly related to the amount of fuel burnt by vehicles in the footprint area. The estimated emission factor for the fleet mix in the measurement area was, in number 1.8 x 10(11) particle veh(-1) km(-1) (for 0.25-2.5 mu m size range). Assuming spherical particles of density 1600 kg m(-3) this corresponds to 27.5 mg veh(-1) km(-1). For particles (0.8-2.5 mu m) the emission factors were 5.1 x 10(9) veh(-1) km(-1) for number and 11.5 mg veh(-1) km(-1) for mass. But a wind speed dependence was noted for high wind speeds. Thus, for wind speeds larger than 9 ms(-1), as measured in the tower at 105m (U-105), the emission factor for particle number and mass was parameterised as: E-f(Number, 0.8-2.5 mu m) = (6.1 +/- 1.7)10(9)U(105)-50+/-188 and E-f(Mass, 0.8-2.5 mu m) = (20+/-12)U-105-171+/-122.
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| 9. |
- Vogt, Matthias, et al.
(författare)
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Traffic Aerosol emission velocity derived from direct flux measurements over urban Stockholm, Sweden
- 2011
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 45:32, s. 5725-5731
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Tidskriftsartikel (refereegranskat)abstract
- Size-resolved aerosol vertical number fluxes were measured using the eddy covariance method, 105 meters above the ground over the city of Stockholm, Sweden, between 1st April 2008 and 15th April 2009. The size range of the measurements cover particles from 0.25 to 2.5 μm diameter (Dp). Emission velocities (ve) were calculated for the same size range and were found to be well correlated with friction velocity (u*) and CO2 fluxes (FCO2). These variables were used to parameterize the emission velocity aswhere ve and u* are given in [m s−1], Dp in [μm], and FCO2 in [mmol m−2s−1]. The parameterization reproduces the average diurnal cycle from the observations well for particles sizes up to 0.6 μm Dp. For larger particles the parameterization tends to over predict the emission velocity. These larger particles are not believed to be produced by combustion and therefore not well represented by FCO2, which represents the traffic source through its fossil fuel consumption and the related CO2 emissions.
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