Browsing by Subject "OPTICAL-PROPERTIES"

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  • Pandolfi, Marco; Alados-Arboledas, Lucas; Alastuey, Andres; Andrade, Marcos; Angelov, Christo; Artinano, Begona; Backman, John; Baltensperger, Urs; Bonasoni, Paolo; Bukowiecki, Nicolas; Coen, Martine Collaud; Conil, Sebastien; Coz, Esther; Crenn, Vincent; Dudoitis, Vadimas; Ealo, Marina; Eleftheriadis, Kostas; Favez, Olivier; Fetfatzis, Prodromos; Fiebig, Markus; Flentje, Harald; Ginot, Patrick; Gysel, Martin; Henzing, Bas; Hoffer, Andras; Smejkalova, Adela Holubova; Kalapov, Ivo; Kalivitis, Nikos; Kouvarakis, Giorgos; Kristensson, Adam; Kulmala, Markku; Lihavainen, Heikki; Lunder, Chris; Luoma, Krista; Lyamani, Hassan; Marinoni, Angela; Mihalopoulos, Nikos; Moerman, Marcel; Nicolas, Jose; O'Dowd, Colin; Petäjä, Tuukka; Petit, Jean-Eudes; Pichon, Jean Marc; Prokopciuk, Nina; Putaud, Jean-Philippe; Rodriguez, Sergio; Sciare, Jean; Sellegri, Karine; Swietlicki, Erik; Titos, Gloria; Tuch, Thomas; Tunved, Peter; Ulevicius, Vidmantas; Vaishya, Aditya; Vana, Milan; Virkkula, Aki; Vratolis, Stergios; Weingartner, Ernest; Wiedensohler, Alfred; Laj, Paolo (2018)
    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.
  • Laj, Paolo; Bigi, Alessandro; Rose, Clemence; Andrews, Elisabeth; Myhre, Cathrine Lund; Coen, Martine Collaud; Lin, Yong; Wiedensohler, Alfred; Schulz, Michael; Ogren, John A.; Fiebig, Markus; Gliss, Jonas; Mortier, Augustin; Pandolfi, Marco; Petäjä, Tuukka; Kim, Sang-Woo; Aas, Wenche; Putaud, Jean-Philippe; Mayol-Bracero, Olga; Keywood, Melita; Labrador, Lorenzo; Aalto, Pasi; Ahlberg, Erik; Alados Arboledas, Lucas; Alastuey, Andres; Andrade, Marcos; Artinano, Begona; Ausmeel, Stina; Arsov, Todor; Asmi, Eija; Backman, John; Baltensperger, Urs; Bastian, Susanne; Bath, Olaf; Beukes, Johan Paul; Brem, Benjamin T.; Bukowiecki, Nicolas; Conil, Sebastien; Couret, Cedric; Day, Derek; Dayantolis, Wan; Degorska, Anna; Eleftheriadis, Konstantinos; Fetfatzis, Prodromos; Favez, Olivier; Flentje, Harald; Gini, Maria I.; Gregoric, Asta; Gysel-Beer, Martin; Hallar, A. Gannet; Hand, Jenny; Hoffer, Andras; Hueglin, Christoph; Hooda, Rakesh K.; Hyvärinen, Antti; Kalapov, Ivo; Kalivitis, Nikos; Kasper-Giebl, Anne; Kim, Jeong Eun; Kouvarakis, Giorgos; Kranjc, Irena; Krejci, Radovan; Kulmala, Markku; Labuschagne, Casper; Lee, Hae-Jung; Lihavainen, Heikki; Lin, Neng-Huei; Loeschau, Gunter; Luoma, Krista; Marinoni, Angela; Dos Santos, Sebastiao Martins; Meinhardt, Frank; Merkel, Maik; Metzger, Jean-Marc; Mihalopoulos, Nikolaos; Nhat Anh Nguyen,; Ondracek, Jakub; Perez, Noemi; Perrone, Maria Rita; Petit, Jean-Eudes; Picard, David; Pichon, Jean-Marc; Pont, Veronique; Prats, Natalia; Prenni, Anthony; Reisen, Fabienne; Romano, Salvatore; Sellegri, Karine; Sharma, Sangeeta; Schauer, Gerhard; Sheridan, Patrick; Sherman, James Patrick; Schuetze, Maik; Schwerin, Andreas; Sohmer, Ralf; Sorribas, Mar; Steinbacher, Martin; Sun, Junying; Titos, Gloria; Toczko, Barbara; Tuch, Thomas; Tulet, Pierre; Tunved, Peter; Vakkari, Ville; Velarde, Fernando; Velasquez, Patricio; Villani, Paolo; Vratolis, Sterios; Wang, Sheng-Hsiang; Weinhold, Kay; Weller, Rolf; Yela, Margarita; Yus-Diez, Jesus; Zdimal, Vladimir; Zieger, Paul; Zikova, Nadezda (2020)
    Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.
  • Hussein, Tareq; Juwhari, Hassan; Al Kuisi, Mustafa; Alkattan, Hamza; Lahlouh, Bashar; Al-Hunaiti, Afnan (2018)
    In this study, we analyzed the concentrations of accumulation and coarse modes measured during November 2013–July 2017 at an urban background site in Amman, Jordan. The concentrations showed distinct seasonal variations with high concentrations with a monthly average higher than 100 cm−3 and 1.5 cm−3, respectively, for accumulation and coarse modes during the winter and low concentrations with a monthly average less than 40 cm−3 and 1–1.5 cm−3, respectively, for accumulation and coarse modes during the summer. Sand and dust storms (SDS) affected the coarse mode during the early spring whereas local dust re-suspension affected them during the autumn. The gravimetric analysis confirmed the seasonal variation of the calculated particulate mass concentration but suggested that the assumption of spherical particles and unit density is not always proper. The ATR-FTIR analysis of selected filters revealed that aerosols in the background atmosphere of Amman are a mixture of locally emitted (fossil fuel combustion) and local/regional dust. Based on the 24-h average of the calculated PM10, the pollution standard index (PSI) revealed that about 81% of the days were either good or moderate air quality conditions. About 71% of the days were below the 24-h PM10 limit value according to the Jordanian air quality standards (120 μg m−3).
  • Virkkula, Aki; Pohja, Toivo; Aalto, Pasi P.; Keronen, Petri; Schobesberger, Siegfried; Clements, Craig B.; Petäjä, Tuukka; Nikmo, Juha; Kulmala, Markku (2014)
  • Fiedler, Stephanie; Kinne, Stefan; Huang, Wan Ting Katty; Räisänen, Petri; O'Donnell, Declan; Bellouin, Nicolas; Stier, Philip; Merikanto, Joonas; van Noije, Twan; Makkonen, Risto; Lohmann, Ulrike (2019)
    This study assesses the change in anthropogenic aerosol forcing from the mid-1970s to the mid-2000s. Both decades had similar global-mean anthropogenic aerosol optical depths but substantially different global distributions. For both years, we quantify (i) the forcing spread due to model-internal variability and (ii) the forcing spread among models. Our assessment is based on new ensembles of atmosphere-only simulations with five state-of-the-art Earth system models. Four of these models will be used in the sixth Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016). Here, the complexity of the anthropogenic aerosol has been reduced in the participating models. In all our simulations, we prescribe the same patterns of the anthropogenic aerosol optical properties and associated effects on the cloud droplet number concentration. We calculate the instantaneous radiative forcing (RF) and the effective radiative forcing (ERF). Their difference defines the net contribution from rapid adjustments. Our simulations show a model spread in ERF from -0.4 to -0.9 W m(-2). The standard deviation in annual ERF is 0.3 W m(-2), based on 180 individual estimates from each participating model. This result implies that identifying the model spread in ERF due to systematic differences requires averaging over a sufficiently large number of years. Moreover, we find almost identical ERFs for the mid-1970s and mid-2000s for individual models, although there are major model differences in natural aerosols and clouds. The model-ensemble mean ERF is -0.54 W m(-2) for the pre-industrial era to the mid-1970s and -0.59 W m(-2) for the pre-industrial era to the mid-2000s. Our result suggests that comparing ERF changes between two observable periods rather than absolute magnitudes relative to a poorly constrained pre-industrial state might provide a better test for a model's ability to represent transient climate changes.
  • Arvola, Lauri; Leppäranta, Matti; Äijälä, Cecilia (2017)
    In lakes and rivers, the concentrations of dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM) are closely related. We analysed three large spectrophotometer data sets of Finnish inland waters from the years 1913–1914, 1913–1931 and 2014 for long-term changes in optical properties. The first data set consists of absorption spectra in the band 467–709 nm of 212 filtered water samples, the second one contains 11– 19 years of data for seven rivers, and the third one contains 153 sites with high resolution spectra over the band 200–750 nm. These data sets were supplemented with more recent monitoring data of DOC. The sites represent typical optical inland water types of north-eastern Europe. The results did not show any consistent large-scale changes in CDOM concentrations over the 101-year time period. The statistics of the absorption coefficients in 1913 and 2014 were almost identical, at 467 nm they were 1.9 ± 1.0 m−1 in 1913 and 1.7 ± 1.2 m−1 in 2014, and the shape of the CDOM absorption spectrum was unchanged, proportional to exp(–S·λ), S = 0.011 nm−1 and λ is wavelength. Catchment properties, primarily lake and peat-land percentages, explained 50% of the variation of CDOM concentration in the lakes, and hydrological conditions explained 50% of the variation of CDOM in the rivers. Both illustrate the importance of catchments and hydrology to CDOM concentrations of boreal inland waters.
  • Zieger, P.; Weingartner, E.; Henzing, J.; Moerman, M.; de Leeuw, G.; Mikkilä, Jyri; Ehn, Mikael; Petäjä, Tuukka; Clemer, K.; van Roozendael, M.; Yilmaz, S.; Friess, U.; Irie, H.; Wagner, T.; Shaiganfar, R.; Beirle, S.; Apituley, A.; Wilson, K.; Baltensperger, U. (2011)
  • Mattinen, Miika; King, Peter J.; Bruener, Philipp; Leskelä, Markku; Ritala, Mikko (2020)
    Semiconducting 2D materials, such as SnS2, hold great promise in a variety of applications including electronics, optoelectronics, and catalysis. However, their use is hindered by the scarcity of deposition methods offering necessary levels of thickness control and large-area uniformity. Herein, a low-temperature atomic layer deposition (ALD) process is used to synthesize up to 5x5 cm(2)continuous, few-layer SnS(2)films on a variety of substrates, including SiO2/Si, Si-H, different ALD-grown films (Al2O3, TiO2, and Ir), sapphire, and muscovite mica. As a part of comprehensive film characterization, the use of low energy ion scattering (LEIS) is showcased to determine film continuity, coverage of monolayer and multilayer areas, and film thickness. It is found that on sapphire substrate, continuous films are achieved at lower thicknesses compared to the other substrates, down to two monolayers or even less. On muscovite mica, van der Waals epitaxial growth is realized after the post-deposition annealing, or even in the as-deposited films when the growth is performed at 175 to 200 degrees C. This work highlights the importance of the substrate choice for 2D materials and presents a practical low-temperature method for the deposition of high-quality SnS(2)films that may be further evaluated for a range of applications.
  • Lihavainen, Heikki; Asmi, Eija; Aaltonen, Veijo; Makkonen, Ulla; Kerminen, Veli-Matti (2015)
    We used more than five years of continuous aerosol measurements to estimate the direct radiative feedback parameter associated with the formation of biogenic secondary organic aerosol (BSOA) at a remote continental site at the edge of the boreal forest zone in Northern Finland. Our upper-limit estimate for this feedback parameter during the summer period (ambient temperatures above 10 degrees C) was -97 +/- 66 mWm(-2) K-1 (mean +/- STD) when using measurements of the aerosol optical depth (f(AOD)) and -63 +/- 40 mWm(-2) K-1 when using measurements of the 'dry' aerosol scattering coefficient at the ground level (f(sigma)). Here STD represents the variability in f caused by the observed variability in the quantities used to derive the value of f. Compared with our measurement site, the magnitude of the direct radiative feedback associated with BSOA is expected to be larger in warmer continental regions with more abundant biogenic emissions, and even larger in regions where biogenic emissions are mixed with anthropogenic pollution.
  • Kalam, Kristjan; Seemen, Helina; Mikkor, Mats; Ritslaid, Peeter; Stern, Raivo; Duenas, Salvador; Castan, Helena; Tamm, Aile; Kukli, Kaupo (2018)
    Atomic layer deposition method was employed to deposit thin films consisting of ZrO2 and HfO2. Zirconia films were doped with hafnia and vice versa, and also nanolaminates were formed. All depositions were carried out at 300 degrees C. Most films were crystalline in their as-deposited state. Zirconia exhibited the metastable cubic and tetragonal phases by a large majority, whereas hafnia was mostly in its stable monoclinic phase. Magnetic and electrical properties of the films were assessed. Un-doped zirconia was ferromagnetic and this property diminished with increasing the amount of hafnia in a film. All films exhibited ferroelectric-like behavior and the polarization curves also changed with respect to the film composition. (C) The Author(s) 2018. Published by ECS.
  • Koskelo, Jaakko; Fugallo, Giorgia; Hakala, Mikko; Gatti, Matteo; Sottile, Francesco; Cudazzo, Pierluigi (2017)
    We present a general picture of the exciton properties of layered materials in terms of the excitations of their single-layer building blocks. To this end, we derive a model excitonic Hamiltonian by drawing an analogy with molecular crystals, which are other prototypical van der Waals materials. We employ this simplified model to analyze in detail the excitation spectrum of hexagonal boron nitride (hBN) that we have obtained from the ab initio solution of the many-body Bethe-Salpeter equation as a function of momentum. In this way, we identify the character of the lowest-energy excitons in hBN, discuss the effects of the interlayer hopping and the electron-hole exchange interaction on the exciton dispersion, and illustrate the relation between exciton and plasmon excitations in layered materials.
  • Bhandari, Janarjan; China, Swarup; Chandrakar, Kamal Kant; Kinney, Greg; Cantrell, Will; Shaw, Raymond A.; Mazzoleni, Lynn R.; Girotto, Giulia; Sharma, Noopur; Gorkowski, Kyle; Gilardoni, Stefania; Decesari, Stefano; Facchini, Maria Cristina; Zanca, Nicola; Pavese, Giulia; Esposito, Francesco; Dubey, Manvendra K.; Aiken, Allison C.; Chakrabarty, Rajan K.; Moosmüller, Hans; Onasch, Timothy B.; Zaveri, Rahul A.; Scarnato, Barbara; Fialho, Paulo; Mazzoleni, Claudio (2019)
    Soot particles form during combustion of carbonaceous materials and impact climate and air quality. When freshly emitted, they are typically fractal-like aggregates. After atmospheric aging, they can act as cloud condensation nuclei, and water condensation or evaporation restructure them to more compact aggregates, affecting their optical, aerodynamic, and surface properties. Here we survey the morphology of ambient soot particles from various locations and different environmental and aging conditions. We used electron microscopy and show extensive soot compaction after cloud processing. We further performed laboratory experiments to simulate atmospheric cloud processing under controlled conditions. We find that soot particles sampled after evaporating the cloud droplets, are significantly more compact than freshly emitted and interstitial soot, confirming that cloud processing, not just exposure to high humidity, compacts soot. Our findings have implications for how the radiative, surface, and aerodynamic properties, and the fate of soot particles are represented in numerical models.
  • Koskelo, J.; Hashemi, J.; Huotari, S.; Hakala, M. (2016)
    We present a comprehensive study of the electronic, magnetic, and optical properties of CuGa1-xFexS2, as a promising candidate for intermediate-band (IB) solar cells. We use hybrid exchange-correlation functional within the density functional theory framework, and show that Fe doping induces unoccupied states 1.6-1.9 eV above the valence band. The IBs significantly enhance the optical absorption in lower energy part of the spectrum. We find that at moderate n-type co-doping concentration, the added charge occupies part of the IB in the gap, but large concentrations lower the energy of the occupied IB toward the valence band. Moreover, we show that Fe impurities tend to cluster within the compound and they choose antiferromagnetic ordering. The findings can have a significant effect in understanding this material and help to synthesize more efficient IB solar cells.
  • Rodriguez, E.; Kolmonen, P.; Virtanen, T. H.; Sogacheva, L.; Sundström, Anu-Maija; de Leeuw, G. (2015)
    The Advanced Along-Track Scanning Radiometer (AATSR) on board the ENVISAT satellite is used to study aerosol properties. The retrieval of aerosol properties from satellite data is based on the optimized fit of simulated and measured reflectances at the top of the atmosphere (TOA). The simulations are made using a radiative transfer model with a variety of representative aerosol properties. The retrieval process utilizes a combination of four aerosol components, each of which is defined by their (lognormal) size distribution and a complex refractive index: a weakly and a strongly absorbing fine-mode component, coarse mode sea salt aerosol and coarse mode desert dust aerosol). These components are externally mixed to provide the aerosol model which in turn is used to calculate the aerosol optical depth (AOD). In the AATSR aerosol retrieval algorithm, the mixing of these components is decided by minimizing the error function given by the sum of the differences between measured and calculated path radiances at 3-4 wavelengths, where the path radiances are varied by varying the aerosol component mixing ratios. The continuous variation of the fine-mode components allows for the continuous variation of the fine-mode aerosol absorption. Assuming that the correct aerosol model (i.e. the correct mixing fractions of the four components) is selected during the retrieval process, also other aerosol properties could be computed such as the single scattering albedo (SSA). Implications of this assumption regarding the ratio of the weakly/strongly absorbing fine-mode fraction are investigated in this paper by evaluating the validity of the SSA thus obtained. The SSA is indirectly estimated for aerosol plumes with moderate-to-high AOD resulting from wildfires in Russia in the summer of 2010. Together with the AOD, the SSA provides the aerosol absorbing optical depth (AAOD). The results are compared with AERONET data, i.e. AOD level 2.0 and SSA and AAOD inversion products. The RMSE (root mean square error) is 0.03 for SSA and 0.02 for AAOD lower than 0.05. The SSA is further evaluated by comparison with the SSA retrieved from the Ozone Monitoring Instrument (OMI). The SSA retrieved from both instruments show similar features, with generally lower AATSR-estimated SSA values over areas affected by wildfires.
  • Lu, Peng; Leppäranta, Matti; Cheng, Bin; Li, Zhijun (2016)
    Solar radiation drives the melting of Arctic sea ice in summer, but its parameterization in thermodynamic modeling is difficult due to the large variability of the optical properties of sea ice in space and time. Here, a two-stream radiative transfer model was developed for the propagation of solar radiation in ponded sea ice to investigate the dependence of apparent optical properties (AOPs), particularly albedo and transmittance, on sky conditions, pond depth, ice thickness, and the inherent optical properties (IOPs) of ice and water. The results of numerical experiments revealed that decrease in melt-pond albedo during melting results not only from increase in pond depth but also from decrease in underlying ice thickness, and the latter is more important for thin ice with thickness less than 1.5 m. Hence, a parameterized pond albedo as a function of both pond depth and ice thickness is more suitable for thinning Arctic sea ice than the previously used exponential function of pond depth, which is valid for thicker ice. The increase in broadband transmittance during melting can be explained by the decrease in underlying ice thickness, because its dependence on ice thickness is nearly three times stronger than on pond depth. The spectral dependence of the pond albedo on depth is significant only in the 600-900-nm band, while it depends clearly on ice thickness in the 350-600-nm band. The uncertainty resulting from the absorption coefficient of ice is limited, while the effect of scattering in ice is more important, as determined by a sensitivity study on the influence of the IOPs on the AOPs of sea ice. The two-stream model provides a time-efficient parameterization of the AOPs for ponded sea ice, accounting for both absorption and scattering, and has potential for implementation into sea-ice thermodynamic models to explain the role of melt ponds in the summer decay of Arctic sea ice. (C) 2016 Elsevier B.V. All rights reserved.
  • de Oliveira, Paulo F. M.; Michalchuk, Adam A. L.; Marquardt, Julien; Feiler, Torvid; Prinz, Carsten; Torresi, Roberto M.; Camargo, Pedro H. C.; Emmerling, Franziska (2020)
    Control over the bottom up synthesis of metal nanoparticles (NP) depends on many experimental factors, including the choice of stabilising and reducing agents. By selectively manipulating these species, it is possible to control NP characteristics through solution-phase synthesis strategies. It is not known, however, whether NPs produced from mechanochemical syntheses are governed by the same rules. Using the Au NPs mechanosynthesis as a model system, we investigate how a series of common reducing agents affect both the reduction kinetics and size of Au NPs. It is shown that the relative effects of reducing agents on mechanochemical NP synthesis differ significantly from their role in analogous solution-phase reactions. Hence, strategies developed for control over NP growth in solution are not directly transferrable to environmentally benign mechanochemical approaches. This work demonstrates a clear need for dedicated, systematic studies on NP mechanosynthesis.
  • Potes, M.; Salgado, R.; Costa, M. J.; Morais, M.; Bortoli, D.; Kostadinov, I.; Mammarella, I. (2017)
    The study of lake-atmosphere interactions was the main purpose of a 2014 summer experiment at Alqueva reservoir in Portugal. Near-surface fluxes of momentum, heat and mass [water vapour (H2O) and carbon dioxide (CO2)] were obtained with the new Campbell Scientific's IRGASON Integrated Open-Path CO2/H2O Gas Analyser and 3D Sonic Anemometer between 2 June and 2 October. On average, the reservoir was releasing energy in the form of sensible and latent heat flux during the study period. At the end of the 75 d, the total evaporation was estimated as 490.26 mm. A high correlation was found between the latent heat flux and the wind speed (R = 0.97). The temperature gradient between air and water was positive between 12 and 21 UTC, causing a negative sensible heat flux, and negative during the rest of the day, triggering a positive sensible heat flux. The reservoir acted as a sink of atmospheric CO2 with an average rate of -0.026 mg m(-2) s(-1). However, at a daily scale we found an unexpected uptake between 0 and 9 UTC and almost null flux between 13 and 19 UTC. Potential reasons for this result are further discussed. The net radiation was recorded for the same period and water column heat storage was estimated using water temperature profiles. The energy balance closure for the analysed period was 81%. In-water solar spectral downwelling irradiance profiles were measured with a new device allowing measurements independent of the solar zenith angle, which enabled the computation of the attenuation coefficient of light in the water column. The average attenuation coefficient for the photosynthetically active radiation spectral region varied from 0.849 +/- 0.025 m(-1) on 30 July to 1.459 +/- 0.007 m(-1) on 25 September.
  • Rajewicz, Paulina A.; Atherton, Jon; Alonso, Luis; Porcar-Castell, Albert (2019)
    Successful measurements of chlorophyll fluorescence (ChlF) spectral properties (typically in the wavelength range of 650-850 nm) across plant species, environmental conditions, and stress levels are a first step towards establishing a quantitative link between solar-induced chlorophyll fluorescence (SIF), which can only be measured at discrete ChlF spectral bands, and photosynthetic functionality. Despite its importance and significance, the various methodologies for the estimation of leaf-level ChlF spectral properties have not yet been compared, especially when applied to leaves with complex morphology, such as needles. Here we present, to the best of our knowledge, a first comparison of protocols for measuring leaf-level ChlF spectra: a custom-made system designed to measure ChlF spectra at ambient and 77 K temperatures (optical chamber, OC), the widely used FluoWat leaf clip (FW), and an integrating sphere setup (IS). We test the three methods under low-light conditions, across two broadleaf species and one needle-like species. For the conifer, we characterize the effect of needle arrangements: one needle, three needles, and needle mats with as little gap fraction as technically possible. We also introduce a simple baseline correction method to account for non-fluorescence-related contributions to spectral measurements. Baseline correction was found especially useful in recovering the spectra nearby the filter cut-off. Results show that the shape of the leaf-level ChlF spectra remained largely unaffected by the measurement methodology and geometry in OC and FW methods. Substantially smaller red/far-red ratios were observed in the IS method. The comparison of needle arrangements indicated that needle mats could be a practical solution to investigate temporal changes in ChlF spectra of needle-like leaves as they produced more reproducible results and higher signals.
  • Ylöstalo, Pasi; Seppälä, Jukka; Kaitala, Seppo; Maunula, Petri; Simis, Stefan (2016)
    We studied the loadings of dissolved organic matter (DOM) and nutrients from the Neva River into the Eastern Gulf of Finland, as well as their distribution within the salinity gradient. Concentrations of dissolved organic carbon (DOC) ranged from 390 to 840 mu M, and were related to absorption of colored DOM (CDOM) at 350 nm, a(CDOM)(350), ranging from 2.70 to 17.8 m(-1). With increasing salinity both DOC and a(CDOM) decreased, whereas the slope of a(CDOM) spectra, S-CDOM(300-700), ranging from 14.3 to 21.2 mu m(-1), increased with salinity. Deviations of these properties from conservative mixing models were occasionally observed within the salinity range of approximately 1-4, corresponding to the region between 27 and 29 degrees E. These patterns are suggested to mostly reflect seasonal changes in properties of river end-member and hydrodynamics of the estuary, rather than non-conservative processes. On the other hand, observed nonlinear relationships observed between a(CDOM)*(350) and S-CDOM(275-295) emphasized the importance of photochemistry among various transformation processes of DOM. Dissolved inorganic nitrogen was effectively transformed in the estuary into particulate organic nitrogen (PON) and dissolved organic nitrogen (DON), of which DON was mostly exported from the estuary, enhancing productivity in nitrogen limited parts of the Gulf of Finland. DON concentrations ranged from 12.4 to 23.5 mu M and its estuarine dynamics were clearly uncoupled from DOC. In contrast to DOC, estuarine DON dynamics suggest that its production exceeds losses in the estuary. Total nitrogen (TN) and phosphorus (TP) loadings from the Neva River and St. Petersburg were estimated as 73.5 Gg N yr(-1) and 4.2 Gg P yr(-1), respectively. Approximately 59% of TN and 53% of TP loads were in organic forms. DOC and DON loadings were estimated as 741.4 Gg C yr(-1) and 19.0 Gg N yr(-1), respectively. Our estimate for DOC loading was evaluated against a previously published carbon budget of the Baltic Sea. According to the updated model, the Baltic Sea could be identified as a weak source of carbon into the atmosphere. (C) 2016 The Authors. Published by Elsevier B.V.
  • Lu, Peng; Cao, Xiaowei; Li, Guoyu; Huan, Wenfeng; Leppäranta, Matti; Arvola, Lauri; Huotari, Jussi; Li, Zhijun (2020)
    To improve the understanding of the seasonal evolution of the mass and heat budget of ice-covered lakes in the cold and arid climate zone, in-situ observations were collected during two winters (2016-2017 and 2017-2018) in Lake Wuliangsuhai, Inner Mongolia, China. The mean snow thickness was 5.2 and 1.6 cm in these winters, due to low winter precipitation. The mean ice thickness was 50.9 and 36.1 cm, and the ice growth rate was 3.6 and 2.1 mm day(-1) at the lower boundary of ice. Analyses of mass and heat balance data from two winters revealed that the surface heat budget was governed by solar radiation and terrestrial radiation. The net heat flux loss of the ice was 9-22 W m(-2), affected by the snow and ice thickness. Compared to boreal lakes, Lake Wuliangsuhai received more solar radiation and heat flux from the water. The ice temperature had a strong diurnal variation, which was produced by the diurnal cycles of solar radiation, and air and water temperatures. These results expand our knowledge of the evolution of mass and heat balance in temperate lakes of mid-latitude arid areas.