Theoretical study of the OH-initiated atmospheric oxidation mechanism of perfluoro methyl vinyl ether, CF_3OCF=CF_2

Product formation in the reaction of perfluorinated methyl vinyl ether, CF_3OCF=CF_2, with OH radicals is studied theoretically using the M06-2X/aug-cc-pVTZ and CCSD(T) levels of theory. The stable end-products in an oxidative atmosphere are predicted to be perfluorinated methyl formate, CF_3OCFO, and fluorinated glycolaldehyde, CFOCF_2OH, both with CF_2O as coproduct. The prediction of glycolaldehyde as a product contrasts with experimental data, which found perfluoro glyoxal, CFOCFO, instead. The most likely explanation for this apparent disagreement is conversion of CFOCF_2OH to CFOCFO, e.g. by multiple catalytic agents present in the reaction mixture, wall reactions, and/or photolysis. The formation routes for the glyoxal product proposed in earlier work appear unlikely, and are not supported by theoretical or related experimental work

On the information content of incubation studies

The measurement of the production of CO2 from soils in incubation studies has been used for many years to gain information about the influence of different soils types, changing temperatures and water contents, as well as the addition of amendments on the soil respiration. While in the early years the kinetic modelling (or fitting) was restricted to the single or one pool model due to the possibility of solving the problem by log-transforming the observed data an using a linear regression for the estimation of the rate constant (by doing so an analytical solution can be applied), more recent publications chose multi-pool models (2, 3, and even 4-pools), which can will be fitted iteratively using appropriate computer software. In general, there are different methods used in literature to estimate the kinetic parameters resulting in different kinetic parameter values even for the same data set. Additionally, screening of existing literature revealed that the 2-pool model (or even higher pool models) were sometimes obviously wrong fitted or over fitted. In our presentation, we will show how different constrains in the fitting process will influence the results of the kinetic parameter values, how obviously wrong fitting and overfitting can be easily detected, and how the information content of the incubation data can be easily judged prior any fitting. Finally, we will provide recommendations how to extract information from incubation experiments

Deriving soil hydraulic parameters in a high spatial resolution for a heterogeneous agricultural field-site

Providing information about the structure of the subsurface plays an important role for setting up soil hydraulic models, which are in turn an important prerequisite for ecosystem modelling approaches. Because soils often show a high within-field heterogeneity in terms of texture, stone content, and bulk density, they may also exhibit a wide range of hydraulic properties in the field. During water stress periods and especially on agricultural fields, which are characterized by uniform vegetation, the occurrence of a within-field heterogeneity in terms of soil hydraulic properties can be observed as it affects the different water status of the plants. The patterns of visible plant water stress and areas of low apparent electrical conductivities measured by electromagnetic induction measurements (EMI) often coincide, for e.g. within sugar beet cropped fields. Such observations have also been made beforehand at the current study site; an agricultural field (2.7 ha) that is situated in an area developed by fluvial processes. To account for this, the current approach included a sampling campaign on a field with 70 drilling locations for texture and organic carbon analyses. Furthermore, soil water retention functions and saturated hydraulic conductivity were determined at 20 sampling locations. Our approach for ecosystem modelling is based on 4 m² grid cells over the whole study site. To consider within-field heterogeneity in the ecosystem model, soil hydraulic parameters were predicted for each grid cell, whereby different approaches such as spatial interpolation, Miller-Miller scaling, and the use of pedotransfer functions were taken into account to identify the most appropriate approach

Transmissão materno-fetal de diferentes subtipos de HIV-1 entre gestantes infectadas na Nigéria

The rate of mother-to-child transmission (MTCT) of HIV as well as the implications of the circulating multiple subtypes to MTCT in Nigeria are not known. This study was therefore undertaken to determine the differential rates of MTCT of HIV-1 subtypes detected among infected pregnant women before ARV intervention therapy became available in Nigeria. Twenty of the HIV-positive women who signed the informed consent form during pregnancy brought their babies for follow-up testing at age 18-24 months. Plasma samples from both mother and baby were tested for HIV antibody at the Department of Virology, UCH, Ibadan, Nigeria. All positive samples (plasma and peripheral blood mononuclear cells - PBMCs) were shipped to the Institute of Tropical Medicine, Antwerp, Belgium, where the subtype of the infecting virus was determined using the HMA technique. Overall, a mother-to-child HIV transmission rate of 45% was found in this cohort. Specifically, 36.4%, 66.7% and 100% of the women infected with HIV-1 CRF02 (IbNg), G and B, respectively, transmitted the virus to their babies. As far as it can be ascertained, this is the first report on the rate of MTCT of HIV in Nigeria. The findings reported in this paper will form a useful reference for assessment of currently available therapeutic intervention of MTCT in the country.A taxa de transmissão materno-fetal (MTCT) do HIV bem como as implicações dos múltiplos subtipos circulantes para MTCT na Nigéria não são conhecidos. Este estudo foi realizado para determinar as diferentes taxas de MTCT dos subtipos de HIV-1 detectados entre gestantes infectadas antes que a administração da terapia ARV estivesse disponível na Nigéria. Vinte das mulheres HIV positivas que assinaram o consentimento durante a gravidez trouxeram seus filhos para seguimento na idade de 18-24 meses. Amostras de plasma de ambos, mãe e filho foram testadas para anticorpos HIV no Departamento de Virologia, UCH, Ibadan, Nigéria. Todas as amostras positivas (plasma e células mononucleares do sangue periférico - PBMCs) foram enviadas para o Instituto de Medicina Tropical da Antuérpia, Bélgica, onde os subtipos de vírus infectantes foram determinados utilizando-se a técnica HMA. No conjunto, uma taxa de transmissão de HIV, materno-fetal, de 45% foi encontrada neste grupo. Especificamente, 36,4%, 66,7% e 100% das mulheres infectadas com HIV-1 CRF02 (IbNg), G e B, respectivamente, transmitiram o vírus para seus filhos. Até onde pode ser verificado, este é o primeiro relato da taxa de MTCT do HIV na Nigéria. Os achados relatados neste trabalho serão uma útil referência para estimar a qualidade das terapêuticas atuais disponíveis para MTCT neste país

Reproducibility and validity of a diet quality index for children assessed using a FFQ

The diet quality index (DQI) for preschool children is a new index developed to reflect compliance with four main food-based dietary guidelines for preschool children in Flanders. The present study investigates: (1) the validity of this index by comparing DQI scores for preschool children with nutrient intakes, both of which were derived from 3d estimated diet records; (2) the reproducibility of the DQI for preschoolers based on a parentally reported forty-seven-item FFQ DQI, which was repeated after 5 weeks; (3) the relative validity of the FFQ DQI with 3d record DQI scores as reference. The study sample included 510 and 58 preschoolers (2-5-6.5 years) for validity and reproducibility analyses, respectively. Increasing 3d record DQI scores were associated with decreasing consumption of added sugars, and increasing intakes of fibre, water, Ca and many micronutrients. Mean FFQ DQI test-retest scores were not significantly different: 72 (so 11) v. 71 (Si) 10) (P-=0-218) out of a maximum of 100. Mean 3d record DQI score (66 (so 10)) was significantly lower than mean FFQ DQI (71 (so 10);

The atmospheric impacts of monoterpene ozonolysis on global stabilised Criegee intermediate budgets and SO2 oxidation : experiment, theory and modelling

The gas-phase reaction of alkenes with ozone is known to produce stabilised Criegee intermediates (SCIs). These biradical/zwitterionic species have the potential to act as atmospheric oxidants for trace pollutants such as SO₂, enhancing the formation of sulfate aerosol with impacts on air quality and health, radiative transfer and climate. However, the importance of this chemistry is uncertain as a consequence of limited understanding of the abundance and atmospheric fate of SCIs. In this work we apply experimental, theoretical and numerical modelling methods to quantify the atmospheric impacts, abundance and fate of the structurally diverse SCIs derived from the ozonolysis of monoterpenes, the second most abundant group of unsaturated hydrocarbons in the atmosphere. We have investigated the removal of SO₂ by SCIs formed from the ozonolysis of three atmospherically important monoterpenes (<i>α</i>-pinene, <i>β</i>-pinene and limonene) in the presence of varying amounts of water vapour in large-scale simulation chamber experiments that are representative of boundary layer conditions. The SO₂ removal displays a clear dependence on water vapour concentration, but this dependence is not linear across the range of [H₂O] explored. At low [H₂O] a strong dependence of SO₂ removal on [H₂O] is observed, while at higher [H₂O] this dependence becomes much weaker. This is interpreted as being caused by the production of a variety of structurally (and hence chemically) different SCIs in each of the systems studied, which displayed different rates of reaction with water and of unimolecular rearrangement or decomposition. The determined rate constants, <i>k</i>(SCI+H₂O), for those SCIs that react primarily with H₂O range from 4 to 310  ×  10⁻¹⁵ cm³ s⁻¹. For those SCIs that predominantly react unimolecularly, determined rates range from 130 to 240 s⁻¹. These values are in line with previous results for the (analogous) stereo-specific SCI system of <i>syn</i>-/<i>anti</i>-CH₃CHOO. The experimental results are interpreted through theoretical studies of the SCI unimolecular reactions and bimolecular reactions with H₂O, characterised for <i>α</i>-pinene and <i>β</i>-pinene at the M06-2X/aug-cc-pVTZ level of theory. The theoretically derived rates agree with the experimental results within the uncertainties. A global modelling study, applying the experimental results within the GEOS-Chem chemical transport model, suggests that &gt; 97 % of the total monoterpene-derived global SCI burden is comprised of SCIs with a structure that determines that they react slowly with water and that their atmospheric fate is dominated by unimolecular reactions. Seasonally averaged boundary layer concentrations of monoterpene-derived SCIs reach up to 1.4  ×  10⁴ cm⁻³ in regions of elevated monoterpene emissions in the tropics. Reactions of monoterpene-derived SCIs with SO₂ account for &lt; 1 % globally but may account for up to 60 % of the gas-phase SO₂ removal over areas of tropical forests, with significant localised impacts on the formation of sulfate aerosol and hence the lifetime and distribution of SO₂

Nitrogen backbone oligomers

In contrast to carbon, which forms long polymeric chains, all-nitrogen chains are very unstable. Here we found that nitrogen and hydrogen directly react at room temperature and pressures of about 35 GPa forming a mixture of nitrogen backbone oligomers - chains of single-bonded nitrogen atom with the rest of the bonds terminated with hydrogen atoms - as identified by IR absorption, Raman, X-ray diffraction experiments and theoretical calculations. The pressure required for the synthesis strongly decreases with temperature to about 20 GPa at 550 K. At releasing pressures below about 10 GPa, the product transforms into hydrazine. Our findings might open a way for the practical synthesis of these extremely high energetic materials as the formation of nitrogen-hydrogen compounds is favorable already at pressures above 2 GPa according to the calculations.Comment: 34 pages, 21 figure

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO₂, H₂O and dimethyl sulfide

Isoprene is the dominant global biogenic volatile organic compound (VOC) emission. Reactions of isoprene with ozone are known to form stabilised Criegee intermediates (SCIs), which have recently been shown to be potentially important oxidants for SO2 and NO2 in the atmosphere; however the significance of this chemistry for SO2 processing (affecting sulfate aerosol) and NO2 processing (affecting NOx levels) depends critically upon the fate of the SCIs with respect to reaction with water and decomposition. Here, we have investigated the removal of SO2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene-derived SCIs with H2O. Under excess SO2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (+/-0.03). The observed SO2 removal kinetics are consistent with a relative rate constant, k (SCI + H2O) = k (SCI + SO2), of 3.1 (+/-0.5) x 10(-5) for isoprene-derived SCIs. The relative rate constant for k (SCI decomposition) = k (SCI + SO2) is 3.0 (+/-3.2) x 10(11) cm(-3). Uncertainties are +/-2 sigma and represent combined systematic and precision components. These kinetic parameters are based on the simplification that a single SCI species is formed in isoprene ozonolysis, an approximation which describes the results well across the full range of experimental conditions. Our data indicate that isoprenederived SCIs are unlikely to make a substantial contribution to gas-phase SO2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO2 removal in the isopreneozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCIs and dimethyl sulfide (DMS); the observed SO2 removal kinetics are consistent with a relative rate constant, k (SCI + DMS) = k (SCI + SO2), of 3.5 (+/-1.8). This result suggests that SCIs may contribute to the oxidation of DMS in the atmosphere and that this process could therefore influence new particle formation in regions impacted by emissions of unsaturated hydrocarbons and DMS

Simulation of spatial variability in crop leaf area index and yield using agroecosystem modeling and geophysics-based quantitative soil information

Agroecosystem models that simulate crop growth as a function of weather conditionsand soil characteristics are among the most promising tools for improving crop yield and achieving more sustainable agricultural production systems. This study aims at using spatially distributed crop growth simulations to investigate how field-scale patterns in soil properties obtained using geophysical mapping affect the spatial variability of soil water content dynamics and growth of crops at the square kilometer scale. For this, a geophysics-based soil map was intersected with land use information. Soilhydraulic parameters were calculated using pedotransfer functions. Simulations of soilwater content dynamics performed with the agroecosystem model AgroC were com-pared with soil water content measured at two locations, resulting in RMSE of 0.032and of 0.056 cm3cm−3, respectively. The AgroC model was then used to simulate thegrowth of sugar beet (Beta vulgaris L.), silage maize (Zea maysL.), potato (SolanumtuberosumL.), winter wheat (Triticum aestivumL.), winter barley (Hordeum vulgareL.), and winter rapeseed (Brassica napusL.) in the 1- by 1-km study area. It was found that the simulated leaf area index (LAI) was affected by the magnitude of simulated water stress, which was a function of both the crop type and soil characteristics. Simulated LAI was generally consistent with the observed LAI calculated from normalized difference vegetation index (LAINDVI) obtained from RapidEye satellite data. Finally, maps of simulated agricultural yield were produced for four crops, and it was found that simulated yield matched well with actual harvest data and literature values. Therefore, it was concluded that the information obtained from geophysics-based soilmapping was valuable for practical agricultural applications