Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Electroresponsive polyelectrolyte brushes studied by self-consistent field theory
    Okrugin, Boris M. ; Richter, Ralf P. ; Leermakers, Frans A.M. ; Neelov, Igor M. ; Zhulina, Ekaterina B. ; Borisov, Oleg V. - \ 2020
    e-Polymers 12 (2020)4. - ISSN 1618-7229
    Polyelectrolyte brushes - Self-consistent field theory - Smart interfaces

    End-grafting of polyelectrolyte chains to conducting substrates offers an opportunity to fabricate electro-responsive surfaces capable of changing their physical/chemical properties (adhesion, wettability) in response to applied electrical voltage. We use a self-consistent field numerical approach to compare the equilibrium properties of tethered strong and weak (pH-sensitive) polyelectrolytes to applied electrical field in both salt-free and salt-containing solutions. We demonstrate that both strong and weak polyelectrolyte brushes exhibit segregation of polyions in two populations if the surface is oppositely charged with respect to the brush. This segregation gives rise to complex patterns in the dependence of the brush thickness on salt concentration. We demonstrate that adjustable ionization of weak polyelectrolytes weakens their conformational response in terms of the dependence of brush thickness on the amplitude of the applied voltage.

    Land governance from a mobilities perspective
    Richter, Christine ; Derkzen, Marthe ; Zoomers, Annelies - \ 2020
    Land 9 (2020)2. - ISSN 2073-445X
    Automated Processing of Sentinel-2 Products for Time-Series Analysis in Grassland Monitoring
    Hardy, Tom ; Franceschini, Marston Domingues ; Kooistra, Lammert ; Novani, Marcello ; Richter, Sebastiaan - \ 2020
    In: International Symposium on Environmental Software Systems (ISESS 2020) Wageningen : Springer (IFIP Advances in Information and Communication Technology ) - ISBN 9783030398149 - p. 48 - 56.
    Effective grassland management practices require a good understanding of soil and vegetation properties, that can be quantified by farmers’ knowledge and remote sensing techniques. Many systems have been proposed in the past for grassland monitoring, but open-source alternatives are increasingly being preferred. In this paper, a system is proposed to process data in an open-source and automated way. This system made use of Sentinel-2 data to support grassland management at Haus Riswick in the region around Kleve, Germany, retrieved with help of a platform called Sentinelsat that was developed by ESA. Consecutive processing steps consisted of atmospheric correction, cloud masking, clipping the raster data, and calculation of vegetation indices. First results from 2018 resembled the mowing regime of the area with four growing cycles, although outliers were detected due to a lack of data caused by cloud cover. Moreover, that year’s extremely dry summer was visible in the time-series pattern as well. The proposed script is a primary version of a processing chain, which is suitable to be further expanded for more advanced data pre-processing and data analysis in the future.
    Complexity in inequality
    Mirza, Usman - \ 2020
    Wageningen University. Promotor(en): M. Scheffer, co-promotor(en): E.H. van Nes; A.P. Richter. - Wageningen : Wageningen University - ISBN 9789463951852 - 130

    This thesis explores three interrelated research streams. First, I am interested in the very fundamental and ancient question about the functioning of our societies – why are some individuals or countries rich and others poor? Under this broad question, I aim to understand the drivers of inequality, that traverse the artificial boundaries between economic, social and natural sciences. Second, I study inequality, as being complex and governed by highly interconnected processes such as technology, globalization, trade and migration. These processes can be highly nonlinear causing cyclical behaviour and/or critical transitions such as tipping points. Third, using dynamic models and empirical data, I explain the flow of information between heterogeneous agents, including individuals, households or countries, and how these interactions define the emergent dynamics of inequality. Heterogeneous individuals interact not only inside economic systems but also across systems, such as with the environment and climate. Furthermore, these interactions are governed by formal and informal rules, such as institutions, social norms and agreements.

    Implications of Allee effects for fisheries management in a changing climate: evidence from Atlantic cod
    Winter, Anna Marie ; Richter, Andries ; Eikeset, Anne Maria - \ 2020
    Ecological Applications 30 (2020)1. - ISSN 1051-0761
    Allee effect - Atlantic cod - climate - collapse - fisheries management - hysteresis - marginal effect - proactive management - recovery - regime shift - resilience - tipping points

    There are concerns that increasing anthropogenic stressors can cause catastrophic transitions in ecosystems. Such shifts have large social, economic, and ecological consequences and therefore have important management implications. A potential mechanism behind these regime shifts is the Allee effect, which describes the decline in realized per capita growth rate at small population density. With an age-structured population model for Atlantic cod, Gadus morhua, we illustrate how interactions between human-induced stressors, such as fishing and climate change, can worsen the impact of an Allee effect on populations by promoting hysteresis. Therefore, the risk of population collapse and recovery failure is exacerbated and the success of preventing and reverting collapse depends on the climate regime. We find that, in presence of the Allee effect, a fishing moratorium is only sufficient for recovery when sea surface temperature rise remains within 2°C and fishing is restricted within 10 yrs. If sea surface temperature rises beyond 2°C, even immediate banning of fishing is not sufficient to guarantee recovery. If fishing is not fully banned and a residual fishing pressure remains, the probability of recovery is further decreased, also in the absence of an Allee effect. The results underscore the decisive role of Allee effects for the management of depleted populations in an increasingly human-dominated world. Once the population collapses and its growth rate is suppressed, rebuilding measures will be squandered and collapse will very likely be irreversible. We therefore emphasize the need for proactive management involving precautionary, adaptive measures and reference points. Our studies shows that climate change has the potential to strengthen Allee effects, which could increasingly challenge fisheries management.

    Tragedy, property rights, and the commons: Investigating the causal relationship from institutions to ecosystem collapse
    Isaksen, Elisabeth Thuestad ; Richter, Andries - \ 2019
    Journal of the Association of Environmental and Resource Economists 6 (2019)4. - ISSN 2333-5955 - p. 741 - 781.
    Catch shares - Common pool resource - Endogenous institutions - Fisheries - Instrumental variable - Property rights

    Do private property rights mitigate overexploitation of common pool resources and, if so, under which circumstances? In this paper, we examine the effects of private property rights on the status of marine fisheries by combining data on ecological, economic, and institutional characteristics into a panel data set, spanning over 50 years, 170 exclusive economic zones, and 800 species. To address the inherent endogeneity problem of policy implementation, we employ both a difference-in-differences (DiD) and instrumental variable (IV) strategy. Results from both estimations suggest that property rights lower the probability of a fish stock collapsing, but the effect varies with country and species characteristics. Specifically, we find evidence suggesting that property rights are more effective when ownership is transferable, the general level of ownership protection is strong, trade openness is high, the regenerative capacity of the resource is high, and the species value is high.

    Overcapitalization and social norms of cooperation in a small-scale fishery
    Schaap, Robbert ; Richter, Andries - \ 2019
    Ecological Economics 166 (2019). - ISSN 0921-8009
    Cooperation - Evolutionary game theory - Fisheries - Investment - Overcapacity - Social norms - Social-ecological systems - Technological efficiency

    The increasing technological efficiency of harvesting equipment has been identified as one of the main causes of overcapacity and overexploitation of natural resources. In this paper, a formal model is developed which studies the effects of technological efficiency as an endogenous variable within a bioeconomic system. We model capital investments in a fishery, where investment decisions are made less frequently than the allocation of variable inputs. We study how the possibility to invest in capital affects open access dynamics, and also the evolution of cooperative harvesting norms. We find that the possibility to make large capital investments can destabilize cooperation, especially if enforcement capacity is low. Further, we find that communities can preserve cooperation by agreeing on a resource level that is lower than socially-optimal. This reduces the incentive to deviate from the cooperative strategy and invest in capital.

    Positive framing does not solve the tragedy of the commons
    Isaksen, Elisabeth Thuestad ; Brekke, Kjell Arne ; Richter, Andries - \ 2019
    Journal of Environmental Economics and Management 95 (2019). - ISSN 0095-0696 - p. 45 - 56.
    Common pool experiment - Externality - Framing - Public goods experiment - Rivalry - Strategic complements - Strategic substitutes

    We investigate whether positive framing increases cooperation in three social dilemmas with slightly different properties: a linear public goods (PG) game, a non-linear PG game, and a common pool resource (CPR) game. Results from our laboratory experiments show that contributions to a linear PG are higher if the externality is framed positively, rather than negatively, corroborating earlier findings by Andreoni (1995). By contrast, we find no such framing effects in the non-linear PG game or the CPR game. In these games, the best response in the material payoffs is to contribute less if others contribute more, counteracting effects of pro-social preferences. Positive framing therefore does not help to solve the tragedy of the commons.

    Adverse results of the economic crisis : A study on the emergence of enhanced formaldehyde (HCHO) levels seen from satellites over Greek urban sites
    Zyrichidou, I. ; Balis, D. ; Koukouli, M.E. ; Drosoglou, T. ; Bais, A. ; Gratsea, M. ; Gerasopoulos, E. ; Liora, N. ; Poupkou, A. ; Giannaros, C. ; Melas, D. ; Smedt, I. De; Roozendael, M. Van; A, R.J. van der; Boersma, K.F. ; Valks, P. ; Richter, A. - \ 2019
    Atmospheric Research 224 (2019). - ISSN 0169-8095 - p. 42 - 51.
    Biomass burning - GOME-2 instrument - HCHO - NO - Urban air pollution

    In order to study the years of the outbreak of the financial crisis in Greece, we use a continuous eight-year record (2008–2015) of formaldehyde, HCHO, columns retrieved from the GOME-2/MetOp-A and GOME-2/MetOp-B satellite instruments over two urban Greek regions, Thessaloniki and Athens. A statistical linear regression analysis that was applied to the GOME-2/MetOp-A HCHO time series over both cities revealed positive annual changes. On seasonal basis, the wintertime HCHO change per annum was found to be 7.43 ± 2.26% and 6.13 ± 2.12% over Thessaloniki and Athens, respectively. A corresponding seasonal time series analysis was also applied to tropospheric nitrogen dioxide, NO 2 , levels. The tropospheric NO 2 winter change per annum is shown to be negative, at −3.0 ± 0.13% and −3.94 ± 0.14% over Thessaloniki and Athens, respectively. The satellite HCHO and NO 2 observations levels are comparable to collocated ground-based MAX-DOAS measurements. Furthermore, the Comprehensive Air Quality Model with extensions chemical transport model, CAMx CTM, as well as the driving emission inventory in CAMx are used for further investigation of the seasonality of the HCHO concentrations and emissions. The CTM model analysis of the annual HCHO cycle and the winter season anti-correlation between HCHO total columns and surface temperature, mostly over Thessaloniki (R = –0.3), point to the fact that the winter HCHO enhancements, likely connected with enhanced anthropogenic activities, are not being captured by the model. The results of this study indicate a possible enhanced anthropogenic activity during the winter season that was strengthened through the investigation on the origins of the wintertime increase in HCHO columns since the beginning of the economic crisis in the country.

    Technology driven inequality leads to poverty and resource depletion
    Usman Mirza, M. ; Richter, Andries ; Nes, Egbert H. van; Scheffer, Marten - \ 2019
    Ecological Economics 160 (2019). - ISSN 0921-8009 - p. 215 - 226.
    Critical transitions - Dynamic systems - Inequality - Poverty trap - Social-ecological systems - Technology

    The rapid rise in inequality is often seen to go in-hand with resource overuse. Examples include water extraction in Pakistan, land degradation in Bangladesh, forest harvesting in Sub-Saharan Africa and industrial fishing in Lake Victoria. While access to ecosystem services provided by common pool resources mitigates poverty, exclusive access to technology by wealthy individuals may fuel excessive resource extraction and deplete the resource, thus widening the wealth gap. We use a stylised social-ecological model, to illustrate how a positive feedback between wealth and technology may fuel local inequality. The resulting rise in local inequality can lead to resource degradation and critical transitions such as ecological resource collapse and unexpected increase in poverty. Further, we find that societies may evolve towards a stable state of few wealthy and many poor individuals, where the distribution of wealth depends on how access to technology is distributed. Overall, our results illustrate how access to technology may be a mechanism that fuels resource degradation and consequently pushes most vulnerable members of society into a poverty trap.

    Plant science : A regulatory circuit conferring varied flowering response to cold in annual and perennial plants
    Hyun, Youbong ; Vincent, Coral ; Tilmes, Vicky ; Bergonzi, Sara ; Kiefer, Christiane ; Richter, René ; Martinez-Gallegos, Rafael ; Severing, Edouard ; Coupland, George - \ 2019
    Science 363 (2019)6425. - ISSN 0036-8075 - p. 409 - 412.

    The reproductive strategies of plants are highly variable. Short-lived annuals flower abundantly soon after germination, whereas longer-lived perennials postpone and spatially restrict flowering. We used CRISPR/Cas9 and interspecies gene transfer to understand divergence in reproductive patterns between annual and perennial crucifers. We show that in perennial Arabis alpina, flowering in response to winter cold depends on the floral integrator SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 15 (SPL15), whose activity is limited to older shoots and branches during cold exposure. In annuals, this regulatory system is conserved, but cold-induced flowering occurs in young shoots, without requirement for SPL15, through the photoperiodic pathway when plants return to warm. By reconstructing the annual response in perennials, we conclude that characteristic patterns of reproduction in annuals and perennials are conferred through variation in dependency on distinct flowering pathways acting in parallel.

    Meta-analysis of genome-wide association studies of aggressive and chronic periodontitis identifies two novel risk loci
    Munz, Matthias ; Richter, Gesa M. ; Loos, Bruno G. ; Jepsen, Søren ; Divaris, Kimon ; Offenbacher, Steven ; Teumer, Alexander ; Holtfreter, Birte ; Kocher, Thomas ; Bruckmann, Corinna ; Jockel-Schneider, Yvonne ; Graetz, Christian ; Ahmad, Ilyas ; Staufenbiel, Ingmar ; Velde, Nathalie Van Der; Uitterlinden, André G. ; Groot, Lisette C.P.G.M. De; Wellmann, Jürgen ; Berger, Klaus ; Krone, Bastian ; Hoffmann, Per ; Laudes, Matthias ; Lieb, Wolfgang ; Franke, Andre ; Erdmann, Jeanette ; Dommisch, Henrik ; Schaefer, Arne S. - \ 2019
    European Journal of Human Genetics 27 (2019)1. - ISSN 1018-4813 - p. 102 - 113.
    Periodontitis is one of the most common inflammatory diseases, with a prevalence of 11% worldwide for the severe forms and an estimated heritability of 50%. It is classified into the widespread moderate form chronic periodontitis (CP) and the rare early-onset and severe phenotype aggressive periodontitis (AgP). These different disease manifestations are thought to share risk alleles and predisposing environmental factors. To obtain novel insights into the shared genetic etiology and the underlying molecular mechanisms of both forms, we performed a two step-wise meta-analysis approach using genome-wide association studies of both phenotypes. Genotypes from imputed genome-wide association studies (GWAS) of AgP and CP comprising 5,095 cases and 9,908 controls of North-West European genetic background were included. Two loci were associated with periodontitis at a genome-wide significance level. They located within the pseudogene MTND1P5 on chromosome 8 (rs16870060-G, P = 3.69 × 10−9, OR = 1.36, 95% CI = [1.23–1.51]) and intronic of the long intergenic non-coding RNA LOC107984137 on chromosome 16, downstream of the gene SHISA9 (rs729876-T, P = 9.77 × 10−9, OR = 1.24, 95% CI = [1.15–1.34]). This study identified novel risk loci of periodontitis, adding to the genetic basis of AgP and CP.
    The resilience of social norms of cooperation under resource scarcity and inequality — An agent-based model on sharing water over two harvesting seasons
    Nhim, Tum ; Richter, Andries ; Zhu, Xueqin - \ 2019
    Ecological Complexity 40 (2019)B. - ISSN 1476-945X
    Agent-based modeling - Cooperation - Inequality - Resilience - Resource scarcity - Social-ecological systems

    Water governance remains a challenge for human societies, especially when the variation in resource inflow is large and the resource users are heterogeneous. We analyze with a coupled social-ecological systems (SES) model how socioeconomic and environmental changes affect the resilience of social norms governing resource use. In our model, agents have access to water as a common-pool resource and allocate it between rainy and dry seasons. While it is socially optimal to save water for the dry season, it is individually optimal to take water immediately. In our model, punishment of norm violators is the mechanism that may sustain cooperation. We show that the resilience of social norms could be affected by changes in socioeconomic and environmental conditions. Particularly, we find that social norms may collapse in times of resource scarcity and variability, especially if several drivers act in concert. Finally, we find that user heterogeneity in the form of different skills and inequality in land endowments may undermine cooperation. This implies that climatic changes and increased inequality – both potential drivers in the field – may affect community resilience and may lead to an erosion of social norms.

    Improving algorithms and uncertainty estimates for satellite NO2 retrievals : Results from the quality assurance for the essential climate variables (QA4ECV) project
    Boersma, K.F. ; Eskes, Henk J. ; Richter, Andreas ; Smedt, Isabelle De; Lorente, Alba ; Beirle, Steffen ; Geffen, Jos H.G.M. van; Zara, Marina ; Peters, Enno ; Roozendael, Michel Van; Wagner, Thomas ; Maasakkers, Joannes D. ; A, Ronald J. van der; Nightingale, Joanne ; Rudder, Anne De; Irie, Hitoshi ; Pinardi, Gaia ; Lambert, Jean Christopher ; Compernolle, Steven C. - \ 2018
    Atmospheric Measurement Techniques 11 (2018)12. - ISSN 1867-1381 - p. 6651 - 6678.

    Global observations of tropospheric nitrogen dioxide (NO2) columns have been shown to be feasible from space, but consistent multi-sensor records do not yet exist, nor are they covered by planned activities at the international level. Harmonised, multi-decadal records of NO2 columns and their associated uncertainties can provide crucial information on how the emissions and concentrations of nitrogen oxides evolve over time. Here we describe the development of a new, community best-practice NO2 retrieval algorithm based on a synthesis of existing approaches. Detailed comparisons of these approaches led us to implement an enhanced spectral fitting method for NO2, a 1°  ×  1° TM5-MP data assimilation scheme to estimate the stratospheric background and improve air mass factor calculations. Guided by the needs expressed by data users, producers, and WMO GCOS guidelines, we incorporated detailed per-pixel uncertainty information in the data product, along with easily traceable information on the relevant quality aspects of the retrieval. We applied the improved QA4ECV NO2 algorithm to the most current level-1 data sets to produce a complete 22-year data record that includes GOME (1995–2003), SCIAMACHY (2002–2012), GOME-2(A) (2007 onwards) and OMI (2004 onwards). The QA4ECV NO2 spectral fitting recommendations and TM5-MP stratospheric column and air mass factor approach are currently also applied to S5P-TROPOMI. The uncertainties in the QA4ECV tropospheric NO2 columns amount to typically 40 % over polluted scenes. The first validation results of the QA4ECV OMI NO2 columns and their uncertainties over Tai'an, China, in June 2006 suggest a small bias (−2 %) and better precision than suggested by uncertainty propagation. We conclude that our improved QA4ECV NO2 long-term data record is providing valuable information to quantitatively constrain emissions, deposition, and trends in nitrogen oxides on a global scale.

    Genome-wide association meta-analysis of coronary artery disease and periodontitis reveals a novel shared risk locus
    Munz, Matthias ; Richter, Gesa M. ; Loos, Bruno G. ; Jepsen, Søren ; Divaris, Kimon ; Offenbacher, Steven ; Teumer, Alexander ; Holtfreter, Birte ; Kocher, Thomas ; Bruckmann, Corinna ; Jockel-Schneider, Yvonne ; Graetz, Christian ; Munoz, Loreto ; Bhandari, Anita ; Tennstedt, Stephanie ; Staufenbiel, Ingmar ; Velde, Nathalie Van Der; Uitterlinden, André G. ; Groot, Lisette C.P.G.M. De; Wellmann, Jürgen ; Berger, Klaus ; Krone, Bastian ; Hoffmann, Per ; Laudes, Matthias ; Lieb, Wolfgang ; Franke, Andre ; Dommisch, Henrik ; Erdmann, Jeanette ; Schaefer, Arne S. - \ 2018
    Scientific Reports 8 (2018)1. - ISSN 2045-2322
    Evidence for a shared genetic basis of association between coronary artery disease (CAD) and periodontitis (PD) exists. To explore the joint genetic basis, we performed a GWAS meta-analysis. In the discovery stage, we used a German aggressive periodontitis sample (AgP-Ger; 680 cases vs 3,973 controls) and the CARDIoGRAMplusC4D CAD meta-analysis dataset (60,801 cases vs 123,504 controls). Two SNPs at the known CAD risk loci ADAMTS7 (rs11634042) and VAMP8 (rs1561198) passed the pre-assigned selection criteria (PAgP-Ger < 0.05; PCAD < 5 × 10−8; concordant effect direction) and were replicated in an independent GWAS meta-analysis dataset of PD (4,415 cases vs 5,935 controls). SNP rs1561198 showed significant association (PD[Replication]: P = 0.008 OR = 1.09, 95% CI = [1.02–1.16]; PD [Discovery + Replication]: P = 0.0002, OR = 1.11, 95% CI = [1.05–1.17]). For the associated haplotype block, allele specific cis-effects on VAMP8 expression were reported. Our data adds to the shared genetic basis of CAD and PD and indicate that the observed association of the two disease conditions cannot be solely explained by shared environmental risk factors. We conclude that the molecular pathway shared by CAD and PD involves VAMP8 function, which has a role in membrane vesicular trafficking, and is manipulated by pathogens to corrupt host immune defense.
    Structure and properties of polydisperse polyelectrolyte brushes studied by self-consistent field theory
    Okrugin, Boris M. ; Richter, Ralf P. ; Leermakers, Frans A.M. ; Neelov, Igor M. ; Borisov, Oleg V. ; Zhulina, Ekaterina B. - \ 2018
    Soft Matter 14 (2018)30. - ISSN 1744-683X - p. 6230 - 6242.

    Two complementary self-consistent field theoretical approaches are used to analyze the equilibrium structure of binary and ternary brushes of polyions with different degrees of polymerization. Stratification in binary brushes is predicted: the shorter chains are entirely embedded in the proximal sublayer depleted of end-points of longer chains while the peripheral sublayer contains exclusively terminal segments of longer chains. The boundary between sublayers is enriched with counterions that neutralize the residual charge of the proximal sublayer. These analytical predictions for binary brushes are confirmed and extended to ternary brushes using the numerical Scheutjens-Fleer approach.

    The importance of surface reflectance anisotropy for cloud and NO2 retrievals from GOME-2 and OMI
    Lorente, Alba ; Boersma, K.F. ; Stammes, Piet ; Tilstra, L.G. ; Richter, Andreas ; Yu, Huan ; Kharbouche, Said ; Muller, Jan Peter - \ 2018
    Atmospheric Measurement Techniques 11 (2018)7. - ISSN 1867-1381 - p. 4509 - 4529.

    The angular distribution of the light reflected by the Earth's surface influences top-of-atmosphere (TOA) reflectance values. This surface reflectance anisotropy has implications for UV/Vis satellite retrievals of albedo, clouds, and trace gases such as nitrogen dioxide (NO2). These retrievals routinely assume the surface to reflect light isotropically. Here we show that cloud fractions retrieved from GOME-2A and OMI with the FRESCO and OMCLDO2 algorithms have an east-west bias of 10% to 50 %, which are highest over vegetation and forested areas, and that this bias originates from the assumption of isotropic surface reflection. To interpret the across-track bias with the DAK radiative transfer model, we implement the bidirectional reflectance distribution function (BRDF) from the Ross-Li semi-empirical model. Testing our implementation against state-of-the-art RTMs LIDORT and SCIATRAN, we find that simulated TOA reflectance generally agrees to within 1 %. We replace the assumption of isotropic surface reflection in the equations used to retrieve cloud fractions over forested scenes with scattering kernels and corresponding BRDF parameters from a daily high-resolution database derived from 16 years' worth of MODIS measurements. By doing this, the east-west bias in the simulated cloud fractions largely vanishes. We conclude that across-track biases in cloud fractions can be explained by cloud algorithms that do not adequately account for the effects of surface reflectance anisotropy. The implications for NO2 air mass factor (AMF) calculations are substantial. Under moderately polluted NO2 and backwardscattering conditions, clear-sky AMFs are up to 20% higher and cloud radiance fractions up to 40% lower if surface anisotropic reflection is accounted for. The combined effect of these changes is that NO2 total AMFs increase by up to 30% for backward-scattering geometries (and decrease by up to 35% for forward-scattering geometries), which is stronger than the effect of either contribution alone. In an unpolluted troposphere, surface BRDF effects on cloud fraction counteract (and largely cancel) the effect on the clearsky AMF. Our results emphasise that surface reflectance anisotropy needs to be taken into account in a coherent manner for more realistic and accurate retrievals of clouds and NO2 from UV/Vis satellite sensors. These improvements will be beneficial for current sensors, in particular for the recently launched TROPOMI instrument with a high spatial resolution.

    Improved slant column density retrieval of nitrogen dioxide and formaldehyde for OMI and GOME-2A from QA4ECV : Intercomparison, uncertainty characterisation, and trends
    Zara, Marina ; Boersma, K.F. ; Smedt, Isabelle De; Richter, Andreas ; Peters, Enno ; Geffen, Jos H.G.M. van; Beirle, Steffen ; Wagner, Thomas ; Roozendael, Michel Van; Marchenko, Sergey ; Lamsal, Lok N. ; Eskes, Henk J. - \ 2018
    Atmospheric Measurement Techniques 11 (2018)7. - ISSN 1867-1381 - p. 4033 - 4058.

    Nitrogen dioxide (NO2/ and formaldehyde (HCHO) column data from satellite instruments are used for air quality and climate studies. Both NO2 and HCHO have been identified as precursors to the ozone (O3/ and aerosol essential climate variables, and it is essential to quantify and characterise their uncertainties. Here we present an intercomparison of NO2 and HCHO slant column density (SCD) retrievals from four different research groups (BIRA-IASB, IUP Bremen, and KNMI as part of the Quality Assurance for Essential Climate Variables (QA4ECV) project consortium, and NASA) and from the OMI and GOME-2A instruments. Our evaluation is motivated by recent improvements in differential optical absorption spectroscopy (DOAS) fitting techniques and by the desire to provide a fully traceable uncertainty budget for the climate data record generated within QA4ECV. The improved NO2 and HCHO SCD values are in close agreement but with substantial differences in the reported uncertainties between groups and instruments. To check the DOAS uncertainties, we use an independent estimate based on the spatial variability of the SCDs within a remote region. For NO2, we find the smallest uncertainties from the new QA4ECV retrieval (0.8×1015 molec. cm-2 for both instruments over their mission lifetimes). Relative to earlier approaches, the QA4ECV NO2 retrieval shows better agreement between DOAS and statistical uncertainty estimates, suggesting that the improved QA4ECV NO2 retrieval has reduced but not altogether eliminated systematic errors in the fitting approach. For HCHO, we reach similar conclusions (QA4ECV uncertainties of 8-12×1015 molec. cm-2), but the closeness between the DOAS and statistical uncertainty estimates suggests that HCHO uncertainties are indeed dominated by random noise from the satellite's level 1 data. We find that SCD uncertainties are smallest for high top-of-atmosphere reflectance levels with high measurement signal-to-noise ratios. From 2005 to 2015, OMI NO2 SCD uncertainties increase by 1-2%year-1, which is related to detector degradation and stripes, but OMI HCHO SCD uncertainties are remarkably stable (increase <1%year-1) and this is related to the use of Earth radiance reference spectra which reduces stripes. For GOME-2A, NO2 and HCHO SCD uncertainties increased by 7-9 and 11-15%year-1 respectively up until September 2009, when heating of the instrument markedly reduced further throughput loss, stabilising the degradation of SCD uncertainty to <3%year-1 for 2009-2015. Our work suggests that the NO2 SCD uncertainty largely consists of a random component (∼65% of the total uncertainty) as a result of the propagation of measurement noise but also of a substantial systematic component (∼35% of the total uncertainty) mainly from "stripe effects". Averaging over multiple pixels in space and/or time can significantly reduce the SCD uncertainties. This suggests that trend detection in OMI, GOME-2 NO2, and HCHO time series is not limited by the spectral fitting but rather by the adequacy of assumptions on the atmospheric state in the later air mass factor (AMF) calculation step.

    In Vitro Fermentation Behavior of Isomalto/Malto-Polysaccharides Using Human Fecal Inoculum Indicates Prebiotic Potential
    Gu, Fangjie ; Borewicz, Klaudyna ; Richter, Bernadette ; Zaal, Pieter H. van der; Smidt, Hauke ; Buwalda, Pieter L. ; Schols, Henk A. - \ 2018
    Molecular Nutrition & Food Research 62 (2018)12. - ISSN 1613-4125
    Digesta - Enzyme activities - Microbiota - Short chain fatty acids

    Scope: This study characterize intestinal fermentation of isomalto/malto-polysaccharides (IMMPs), by monitoring degradation of IMMPs, production of short chain fatty acids (SCFAs), lactic acid, and succinic acid as well as enzyme activity and microbiota composition. Methods and results: IMMP-94 (94% α-(1→6) glycosidic linkages), IMMP-96, IMMP-27, and IMMP-dig27 (IMMP-27 after removal of digestible starch segments) are fermented batchwise in vitro using human fecal inoculum. Fermentation digesta samples are taken for analysis in time up till 48 h. The fermentation of α-(1→6) glycosidic linkages in IMMP-94, IMMP-96, and IMMP-dig27 starts after 12 h and finishes within 48 h. IMMP-27 fermentation starts directly after inoculation utilizing α-(1→4) linked glucosyl residues; however, the utilization of α-(1→6) linked glucoses is delayed and start only after the depletion of α-(1→4) linked glucose moieties. SCFAs are produced in high amounts with acetic acid and succinic acid being the major products next to propionic acid and butyric acid. The polysaccharide fraction is degraded into isomalto-oligosaccharides (IMOs) mainly by extracellular enzymes. The smaller IMOs are further degraded by cell-associated enzymes. Overall microbial diversity and the relative abundance of Bifidobacterium and Lactobacillus, significantly increase during the fermentation of IMMPs. Conclusion: IMMP containing segments of α-(1→6) linked glucose units are slowly fermentable fibers with prebiotic potential.

    Algorithm theoretical baseline for formaldehyde retrievals from S5P TROPOMI and from the QA4ECV project
    Smedt, Isabelle De; Theys, Nicolas ; Yu, Huan ; Danckaert, Thomas ; Lerot, Christophe ; Compernolle, Steven ; Roozendael, Michel Van; Richter, Andreas ; Hilboll, Andreas ; Peters, Enno ; Pedergnana, Mattia ; Loyola, Diego ; Beirle, Steffen ; Wagner, Thomas ; Eskes, Henk ; Geffen, Jos Van; Folkert Boersma, Klaas ; Veefkind, Pepijn - \ 2018
    Atmospheric Measurement Techniques 11 (2018)4. - ISSN 1867-1381 - p. 2395 - 2426.
    On board the Copernicus Sentinel-5 Precursor (S5P) platform, the TROPOspheric Monitoring Instrument (TROPOMI) is a double-channel, nadir-viewing grating spectrometer measuring solar back-scattered earthshine radiances in the ultraviolet, visible, near-infrared, and shortwave infrared with global daily coverage. In the ultraviolet range, its spectral resolution and radiometric performance are equivalent to those of its predecessor OMI, but its horizontal resolution at true nadir is improved by an order of magnitude. This paper introduces the formaldehyde (HCHO) tropospheric vertical column retrieval algorithm implemented in the S5P operational processor and comprehensively describes its various retrieval steps. Furthermore, algorithmic improvements developed in the framework of the EU FP7-project QA4ECV are described for future updates of the processor. Detailed error estimates are discussed in the light of Copernicus user requirements and needs for validation are highlighted. Finally, verification results based on the application of the algorithm to OMI measurements are presented, demonstrating the performances expected for TROPOMI.
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