| 521. |
- Nieminen, Tuomo, et al.
(författare)
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Global analysis of continental boundary layer new particle formation based on long-term measurements
- 2018
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:19, s. 14737-14756
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric new particle formation (NPF) is an important phenomenon in terms of global particle number concentrations. Here we investigated the frequency of NPF, formation rates of 10 nm particles, and growth rates in the size range of 10-25 nm using at least 1 year of aerosol number size-distribution observations at 36 different locations around the world. The majority of these measurement sites are in the Northern Hemisphere. We found that the NPF frequency has a strong seasonal variability. At the measurement sites analyzed in this study, NPF occurs most frequently in March-May (on about 30 % of the days) and least frequently in December-February (about 10 % of the days). The median formation rate of 10 nm particles varies by about 3 orders of magnitude (0.01-10 cm(-3) s(-1)) and the growth rate by about an order of magnitude (1-10 nm h(-1)). The smallest values of both formation and growth rates were observed at polar sites and the largest ones in urban environments or anthropogenically influenced rural sites. The correlation between the NPF event frequency and the particle formation and growth rate was at best moderate among the different measurement sites, as well as among the sites belonging to a certain environmental regime. For a better understanding of atmospheric NPF and its regional importance, we would need more observational data from different urban areas in practically all parts of the world, from additional remote and rural locations in North America, Asia, and most of the Southern Hemisphere (especially Australia), from polar areas, and from at least a few locations over the oceans.
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| 522. |
- Nilsson, Ernst Douglas, et al.
(författare)
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Baltic Sea Spray Emissions : In Situ Eddy Covariance Fluxes vs. Simulated Tank Sea Spray
- 2021
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the first ever evaluation of sea spray aerosol eddy covariance (EC) fluxes at near coastal conditions and with limited fetch, and the first over water with brackish water (on average 7 ppt). The measurements were made on the island of Garpen in the Baltic Sea (56°23′ N, 16°06′ E) in September 2005. We found that wind speed is a major factor that is driving an exponential increase in sea spray sea salt emissions, comparable to previous studies over waters with higher salinity. We were able to show that the inclusion of a thermodenuder in the EC system allowed for the parallel measurements of the dry unheated aerosol flux (representing both organic and sea salt sea spray emissions) and the heated (300 °C) non-volatile sea salt emissions. This study’s experimental approach also included measurements of the artificial sea spray formed in a tank in locally sampled water at the same location as the EC fluxes. We attempted to use the EC aerosol flux measurements to scale the tank measurements to aerosol emissions in order to derive a complete size distribution for the sea spray emission fluxes below the size range (0.3–2 µm dry diameter) of the optical particle counters (OPCs) in the EC system, covering in total 0.01 µm to 2 µm diameter. In the wind directions with long fetches (corresponding to conditions similar to open sea), we were able to distinguish between the aerosol emission fluxes of dry aerosol and heated non-volatile (sea salt only) in the smallest size bins of the OPC, and could therefore indirectly estimate the organic sea spray fraction. In agreement with several previous ambient and tank experiments deriving the size resolved chemical mass concentration of sea salt and water-insoluble organic sea spray, our EC fluxes showed that sea sprays were dominated by sea salt at sizes ≥1 µm diameter, and by organics at the smallest OPC sizes. Since we used direct measures of the sea spray emission fluxes, we confirmed previous suggestions that this size distribution of sea salt and organics is a signature of sea spray aerosols. We were able to show that two sea salt source parameterizations (Mårtensson et al. (2003) and Salter et al. (2015)) agreed fairly well with our observed heated EC aerosol emission fluxes, as long as their predicted emissions were modified for the actual salinity by shifting the particle diameters proportionally to the cubic rote of the salinity. If, in addition, we added organics to the parameterized sea spray following the mono-layer model by Ellison et al. (1999), the combined sea spray parameterizations for sea salt and organics fell reasonably close to the observed fluxes for diameters > 0.15 µm, while one of them overpredicted the sea spray emissions below this size. The organic mono-layer model by Ellison et al. appeared to be able to explain most of the differences we observed between the aerosol emission fluxes with and without the thermodenuder.
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| 523. |
- Nilsson, Johan, et al.
(författare)
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Salinity-dominated thermohaline circulation in sill basins : can two stable equilibria exist?
- 2010
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 62:2, s. 123-133
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of a salinity-dominated thermohaline circulation in a sill basin is examined using a two-layer model. A prescribed freshwater supply acts to establish a stable stratification, working against a prescribed destabilizing temperature difference. The upper-layer outflow is in geostrophic balance and the upwelling is driven by a fixed energy supply to small-scale vertical mixing. The salinity-dominated flow may have two qualitatively different modes of operation. First, a mixing-limited regime, where the upper layer is shallower than the sill and the flow strength decreases with increasing density difference. Second, an overmixed regime, where the upper layer extends below the sill and the flow strength increases with density difference. Possibly, mixing-limited and overmixed equilibria, with widely different upper-layer depths, can exist for the same external parameters. In such cases, transitions between the two regimes are associated with abrupt changes of the salinity, depth and flow strength. The present results may be of relevance for ocean circulation in glacial climates and for interpretations of marine palaeo data, issues that are briefly discussed in the context of the Arctic Ocean.
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| 524. |
- Olstrup, Henrik, et al.
(författare)
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Seasonal variations in the daily mortality associated with exposure to particles, nitrogen dioxide, and ozone in stockholm, sweden, from 2000 to 2016
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- Urban air pollutant emissions and concentrations vary throughout the year due to various factors, e.g., meteorological conditions and human activities. In this study, seasonal variations in daily mortality associated with increases in the concentrations of PM10 (particulate matter), PM2.5–10 (coarse particles), BC (black carbon), NO2 (nitrogen dioxide), and O3 (ozone) were calculated for Stockholm during the period from 2000 to 2016. The excess risks in daily mortality are presented in single and multi-pollutant models during the whole year and divided into four different seasons, i.e., winter (December–February), spring (March–May), summer (June–August), and autumn (September–November). The excess risks in the single-pollutant models associated with an interquartile range (IQR) increase for a lag 02 during the whole year were 0.8% (95% CI: 0.1–1.4) for PM10, 1.1% (95% CI: 0.4–1.8) for PM2.5–10, 0.5% (95% CI: −0.5–1.5) for BC, −1.5% (95% CI: −0.5–−2.5) for NO2, and 1.9% (95% CI: 1.0–2.9) for O3. When divided into different seasons, the excess risks for PM10 and PM2.5–10 showed a clear pattern, with the strongest associations during spring and autumn, but with weaker associations during summer and winter, indicating increased risks associated with road dust particles during these seasons. For BC, which represents combustion-generated particles, the pattern was not very clear, but the strongest positive excess risks were found during autumn. The excess risks for NO2 were negative during all seasons, and in several cases even statistically significantly negative, indicating that NO2 in itself was not harmful at the concentrations prevailing during the measurement period (mean values < 20 µg m−3). For O3, the excess risks were statistically significantly positive during “all year” in both the single and the multi-pollutant models. The excess risks for O3 in the single-pollutant models were also statistically significantly positive during all seasons.
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| 525. |
- Omstedt, Anders, 1949, et al.
(författare)
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Modelling the contributions to marine acidification from deposited SOx, NOx, and NHx in the Baltic Sea: Past and present situations
- 2015
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Ingår i: Continental Shelf Research. - : Elsevier BV. - 0278-4343 .- 1873-6955. ; 111:B, s. 234-249
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Tidskriftsartikel (refereegranskat)abstract
- © 2015. We have examined the effects of historical atmospheric depositions of sulphate, nitrate, and ammonium from land and shipping on the acid-base balance in the Baltic Sea. The modelling considers the 1750-2014 period, when land and ship emissions changed greatly, with increasing carbon dioxide concentrations, SOx, NOx, and NHx emissions, and nutrient loads.The present results indicate that Baltic Sea acidification due to the atmospheric deposition of acids peaked around 1980, with a pH cumulative decrease of approximately 10-2 in surface waters. This is one order of magnitude less than the cumulative acidification due to increased atmospheric CO2. The acidification contribution of shipping is one order of magnitude less than that of land emissions. However, the pH trend due to atmospheric acids has started to reverse due to reduced land emissions, though the effect of shipping is ongoing.The effect of strong atmospheric acids on Baltic Sea water depends on the region and period studied. The largest total alkalinity sink per surface area is in the south-western Baltic Sea where shipping is intense. Considering the entire Baltic Sea over the 2001-2010 period, the pH changes are approximately -3×10-3 to -11×10-3 and -4×10-4 to -16×10-4 pH units attributable to all emissions and ship emissions only, respectively. The corresponding changes in total alkalinity are approximately -10 to -30μmolkg-1 and -1 to -4μmolkg-1 attributable to all emissions and ship emissions only, respectively.
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| 526. |
- Osterwalder, S., et al.
(författare)
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Comparative study of elemental mercury flux measurement techniques over a Fennoscandian boreal peatland
- 2018
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Ingår i: Atmospheric Environment. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1352-2310 .- 1873-2844. ; 172, s. 16-25
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon (R) dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0-34 cm) was identified by measuring total mercury in eight peat cores (57 +/- 8 ng g(-1), average SE), vascular plant coverage (32-52%), water table level (4.5-14.1 cm) and dissolved gaseous elemental mercury concentrations (28-51 pg L-1) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, alpha = 0.05). Even though the correlation between the Teflon DFC and Aero-DFC was significant (r = 0.76, p < 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m(-2) h(-1)) and REA (2 ng m(-2) h(-1)) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers ( < 0.2 m(2)) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity.
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| 527. |
- Ou, Tinghai, et al.
(författare)
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Evaluation of global climate models in simulating extreme precipitation in China
- 2013
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 65
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Tidskriftsartikel (refereegranskat)abstract
- Variations in extreme precipitation can be described by various indices. In order to evaluate a climate model’s ability to simulate extreme precipitation, gridded extreme precipitation indices from observations are needed. There are two ways to obtain gridded extreme precipitation indices from station-based observations: either through interpolation of station-based extreme indices (EISTA) or estimated from gridded precipitation datasets (EIGRID). In this work, we evaluated these two methods and compared observational extreme precipitation indices in China to those obtained from a set of widely used global climate models. Results show that the difference between the two methods is quite large; and in some cases it is even larger than the difference between model simulations and observed gridded EISTA. Based on the sensitivity of the indices to horizontal resolution, it was suggested that EIGRID is more appropriate for evaluating extreme indices simulated by models. Subsequently, historic simulations of extreme precipitation from 21 CMIP5 (Coupled Model Intercomparison Project Phase 5) global climate models were evaluated against two reanalysis datasets during 1961-2000. It was found that most models overestimate extreme precipitation in the mountain regions in western China and northern China and underestimate extreme precipitation in southern China. In eastern China, these models simulate mean extreme precipitation fairly well. Despite this bias, the temporal trend in extreme precipitation for western China is well captured by most models. However, in eastern China, the trend of extreme precipitation is poorly captured by most models, especially for the so-called southern flood and northern drought pattern. Overall, our results suggest that the dynamics of inter-decadal summer monsoon variability should be improved for better prediction of extreme precipitation by the global climate models
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| 528. |
- Pandolfi, Marco, et al.
(författare)
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A European aerosol phenomenology-6 : scattering properties of atmospheric aerosol particles from 28 ACTRIS sites
- 2018
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:11, s. 7877-7911
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (sigma(sp)) and hemispheric backscattering (sigma(bsp)) coefficients, scattering Angstrom exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of sigma(sp) is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, sigma(sp) also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intraannual variability. At mountain sites, higher sigma(sp) and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher sigma(sp) values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low sigma(sp) values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high sigma(sp) values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of sigma(sp) are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of sigma(sp) are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.
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| 529. |
- Patanen, Minna, et al.
(författare)
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Surface composition of size-selected sea salt particles under the influence of organic acids studied in situ using synchrotron radiation X-ray photoelectron spectroscopy
- 2022
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 2:5, s. 1032-1040
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Tidskriftsartikel (refereegranskat)abstract
- Sea spray aerosols play a key role in the climate system by scattering solar radiation and by serving as cloud condensation nuclei. Despite their importance, the impact of sea spray aerosols on global climate remains highly uncertain. One of the key knowledge gaps in our understanding of sea spray aerosol is the chemical composition of the particle surface, important for various atmospheric chemical processes, as a function of size and bulk composition. Here, we have applied X-ray photoelectron spectroscopy (XPS) to determine the surface composition of both pure inorganic sea salt aerosols and sea salt aerosols spiked with an amino acid (phenylalanine) and a straight chain fatty acid (octanoic acid). Importantly, the use of a differential mobility analyser allowed size-selection of 150, 250 and 350 nm monodisperse aerosol particles for comparison to polydisperse aerosol particles. We observed enrichment of magnesium at the particle surfaces relative to chloride in all aerosols tested, across all particle sizes. Interestingly, the magnitude of this enrichment was dependent on the type of organic present in the solution as well as the particle size. Our results suggest that the observed enrichment in magnesium is an inorganic effect which can be either enhanced or diminished by the addition of organic substances.
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| 530. |
- Rogachevskii, Igor, et al.
(författare)
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Energy- and flux-budget theory for surface layers in atmospheric convective turbulence
- 2022
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:11
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Tidskriftsartikel (refereegranskat)abstract
- The energy- and flux-budget (EFB) theory developed previously for atmospheric stably stratified turbulence is extended to the surface layer in atmospheric convective turbulence. This theory is based on budget equations for turbulent energies and fluxes in the Boussinesq approximation. In the lower part of the surface layer in the atmospheric convective boundary layer, the rate of turbulence production of the turbulent kinetic energy (TKE) caused by the surface shear is much larger than that caused by the buoyancy, which results in three-dimensional turbulence of very complex nature. In the upper part of the surface layer, the rate of turbulence production of TKE due to the shear is much smaller than that caused by the buoyancy, which causes unusual strongly anisotropic buoyancy-driven turbulence. Considering the applications of the obtained results to the atmospheric convective boundary-layer turbulence, the theoretical relationships potentially useful in modeling applications have been derived. The developed EFB theory allows us to obtain a smooth transition between a stably stratified turbulence to a convective turbulence. The EFB theory for the surface layer in a convective turbulence provides an analytical expression for the entire surface layer including the transition range between the lower and upper parts of the surface layer, and it allows us to determine the vertical profiles for all turbulent characteristics, including TKE, the intensity of turbulent potential temperature fluctuations, the vertical turbulent fluxes of momentum and buoyancy (proportional to potential temperature), the integral turbulence scale, the turbulence anisotropy, the turbulent Prandtl number, and the flux Richardson number.
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