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- Evgenieva, Tsvetina, et al.
(författare)
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Three-point observation in the troposphere over Sofia-Plana Mountain,Bulgaria
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:24, s. 9343-9363
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Tidskriftsartikel (refereegranskat)abstract
- Based on a novel combination of approaches and instruments, this article presents campaign-based results from atmospheric boundary layer (ABL) height and aerosol optical depth (AOD) measurements carried out at two different experimental sites in Sofia, as well as from three-point measurements of aerosol number concentrations. Several instruments (lidar (developed by the IE), ceilometer, aerosol particle counter, sun photometer and meteorological sensors) were used in this study. Based on joint interpretation of the instruments' data we assess the influence of the atmospheric aerosol in the planetary boundary layer and the significant influence of aerosol layers and high clouds on AOD values. Measurements of AOD in the city basin gave values in the range 0.22-0.41 for cloud-free skies, and up to around 0.8 under partly cloudy conditions. The information obtained during the two campaigns indicates that aerosol particle concentrations were lower in park areas than along heavy-traffic thoroughfares in the city, but higher than in the mountain area. In conclusion, our study demonstrates the potential of employing a broad array of instruments for the study of boundary layer and aerosol over large, valley-situated and heavily urbanized city areas.
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| 4. |
- Evgenieva, Tsvetina, et al.
(författare)
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Lidar, ceilometer and sun photometer investigation of the aerosol optical characteristics in the troposphere over Sofia, Bulgaria
- 2010
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Ingår i: Comptes Rendus de l'Academie Bulgare des Sciences / Proceedings of the Bulgarian Academy of Sciences. - 1310-1331 .- 2367-5535. ; 63:8, s. 1191-1200
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents the results from planetary boundary layer (PBL) height and aerosol optical depth (AOD) measurements carried out in two different experimental sites in Sofia as well as from three-point measurements of aerosol number concentration.The main aim of the present investigation is to determine optical and microphysical characteristics of the atmospheric aerosol in three points of the valley and their variation during the PBL formation over urban area, park zone and mountain site. Four instruments (lidar, ceilometer, aerosol particle counter and sun photometer) were used in this study.The experimental AOD data obtained at lambda = 500nm gave values in the range from 0.22 to 0.41 in case of cloud-free skies and up to around 0.8 under partly cloudy conditions. Aerosol particle counter data on aerosol-particle concentration variations in the size range 0.3-1 mu m provided supportive information on the evolution of the valley-mountain aerosol in time and height during the mixing layer development. Joint interpretation of sun photometer, aerosol lidar and ceilometer CHM 15k data allow the influence of the main part of the atmospheric aerosol in the planetary boundary layer to be accounted as well as the significant influence of aerosol layers and high clouds on AOD values.
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| 8. |
- Reinap, Ausra, 1973-
(författare)
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Aerosol deposition to coastal forests: a wind tunnel approach
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerodynamically rough surfaces of forests provide for efficient air/ canopy exchange of mass, heat and momentum. In that context, the effects of forest edges come into focus, and therefore, coastal-zone forests constitute aparticular concern. Aerosol-sink modelling is of importance to the global-scalecontext, because sink strengths influence the concentration of aerosol particles in the atmosphere, and that concentration, in turn, influences climate. Dry deposition models are insufficient due to a lack of semi-empirical data and because of difficulties in parameterization of the efficiency (E) with which leaves capture aerosols. Quantifications of such parameters promote possibilities for modelling aerosol-sink processes within various canopy layers. This thesis focuses on studies of sea-salt aerosol dry deposition within models of oak canopies exposed to artificially generated aerosols in a wind tunnel. The overall goal is to advance the understanding of deposition processes in forest ecosystems. Aims are to determine capture efficiencies and deposition velocities (Vd) for oak (Quercus robur L.), to investigate E and Vd dependence on aerosol particle size, wind velocity and vegetation structural elements such as Leaf Area Index (LAI), to explore edge effects on deposition, to relate my results to natural situations in the field, and to address modelling applications. This thesis is a result of five studies. The first study is based on developing awind tunnel approach with a main focus on establishing reference conditions.The next step is to quantify E and provide estimates of how E, with respect toa well defined mass-vs-particle-size distribution, varies with wind speed. To that end, a special wash-off technique is developed. Finally, edge effects ondeposition processes are investigated. Results demonstrate that forest ecosystems would experience substantially increased deposition at edges. The findings suggest that field measurements of deposition in the interior of a forest “island” in an otherwise open landscape would underestimate the deposition to the entire forest. Results clearly indicate needs for further research on the effects of LAI on capture efficiency and deposition velocity. The obtained capture efficiencies can be translated into deposition velocities for trees with a specific leaf area. An increase of Vd with increasing wind speed is found, and is consistent with other studies. Results confirm advantages of the wind tunnel approach, including its ability to enable experiments under controlled conditions. However, several problems require that explicit sub-models be developed of wind-speed dependent effects on leaf posture in the aerosol flow field and that gradients in relative humidity close to leaf surfaces need further attention. The results also propose needs for a range of further experimental investigations regarding aerosol deposition across the complete sea-to-land aerodynamic transition.
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| 9. |
- Reinap, Ausra, 1973-, et al.
(författare)
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Dry deposition of NaCl aerosols: theory and method for a modified leaf-washing technique
- 2010
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Ingår i: Atmospheric Measurement Techniques Discussions. - : Copernicus Publications on behalf of the European Geosciences Union. - 1867-8610. ; 3:4, s. 3851-3876
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Tidskriftsartikel (refereegranskat)abstract
- Within the framework of aerosol deposition to vegetation we present a specially designed leaf wash-off method used in a wind-tunnel based study, where leaves of Quercus robur L. were exposed to NaCl aerosols. We summarise the principles and illustrate the method for two types of substances, the chloride ion and the sodium ion, and for two levels of aerosol exposure prior to leaf washing. On the average, in the low-exposure experiments (S1), the 1st (2nd) wash-off step provided 90% (96%) of the amount of Cl− on the leaves. In the high-exposure experiments (S2) the corresponding values were 96% and 99%. For sodium, the general dynamics resembles that of chloride, but the amounts washed off were, in both series, on the average below what would be expected if the equivalent ratio in the tunnel aerosol were to be preserved. Na+ showed adsorption and/or absorption at the leaf surfaces. The difference between the mean values of the amounts of chloride and of sodium washed off in S1 was not statistically significant, the mean Na+ to Cl− difference as a fraction of Cl− being minus 18%±27%; corresponding values for S2 were minus 16%±9%, however (p<0.05). In the latter case, 101±57 μequiv Na+ per m2 of leaf area were missing for the equivalent relationship 1:1 with Cl− to be met. Although uncertainties are thus large, this indicates the magnitude of the Na+-retention. The method is suitable not only for chloride, an inexpensive and easy-to-handle tracer, but also for sodium under exposure at high aerosol concentrations. Our findings will help design further studies of aerosol/forest interactions.
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| 10. |
- Reinap, Ausra, 1973-, et al.
(författare)
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Forest-edge effects on sea-salt aerosol deposition : a wind-tunnel study using living oak leaves
- 2012
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Ingår i: Boreal environment research. - 1239-6095 .- 1797-2469. ; 17:3-4, s. 193-209
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Tidskriftsartikel (refereegranskat)abstract
- Landscape patchiness creates aerodynamic transitions zones that affect the exchange of nutrients and pollutants between the atmosphere and vegetation. Using an artificially generated NaCl aerosol, with its mass-versus-particle-size distribution characterised by an aerodynamic mean particle diameter of 1.6 µm and a geometrical standard deviation of 1.9, we investigate the forest-edge effect on aerosol deposition within a model oak (Quercus robur L.) canopy in a wind tunnel with a smooth up-wind surface, and provide quantitative estimates of deposition rates within the emulated beach-to-forest transition. The deposition rate is maximal around the forest edge with an enhancement factor in relation to the beach deposition of 2.4 for Cl- and 2.0 for Na+. Results are in reasonable agreement with those obtained from deposition models, field studies, and other wind-tunnel based investigations. We find a tendency towards an edge effect also at the downwind forest end, which is in support of model predictions. Estimates of deposition velocities at the edge are 0.06 cms-1 and 0.05 cms-1 for Cl- and Na+, respectively. Because of the edge effect the model forest’s deposition velocity is enhanced, being 1.4 times higher around the edge in comparison with the entire forest. This suggests that field measurements of deposition in the interior of a forest “island” in an otherwise open landscape would underestimate the deposition to the entire forest. Our results can help improve estimates of aerosol-borne inputs of nutrients or pollutants to forests that would experience shifts in meteorological regimes due to changes in climate and forestry practices, in particular with respect to deciduous species in coastal environments where forest-edge effects might be substantial.
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