Abstract. An algorithm setup for the operational Aerosol Layer Height product for TROPOMI on the Sentinel-5 Precursor mission is described and discussed, applied to GOME-2A data, and evaluated with lidar measurements. The algorithm makes a spectral fit of reflectance at the O2 A band in the near-infrared and the fit window runs from 758 to 770 nm. The aerosol profile is parameterised by a scattering layer with constant aerosol volume extinction coefficient and aerosol single scattering albedo and with a fixed pressure thickness. The algorithm's target parameter is the height of this layer. In this paper, we apply the algorithm to observations from GOME-2A in a number of systematic and extensive case studies, and we compare retrieved aerosol layer heights with lidar measurements. Aerosol scenes cover various aerosol types, both elevated and boundary layer aerosols, and land and sea surfaces. The aerosol optical thicknesses for these scenes are relatively moderate. Retrieval experiments with GOME-2A spectra are used to investigate various sensitivities, in which particular attention is given to the role of the surface albedo. From retrieval simulations with the single-layer model, we learn that the surface albedo should be a fit parameter when retrieving aerosol layer height from the O2 A band. Current uncertainties in surface albedo climatologies cause biases and non-convergences when the surface albedo is fixed in the retrieval. Biases disappear and convergence improves when the surface albedo is fitted, while precision of retrieved aerosol layer pressure is still largely within requirement levels. Moreover, we show that fitting the surface albedo helps to ameliorate biases in retrieved aerosol layer height when the assumed aerosol model is inaccurate. Subsequent retrievals with GOME-2A spectra confirm that convergence is better when the surface albedo is retrieved simultaneously with aerosol parameters. However, retrieved aerosol layer pressures are systematically low (i.e., layer high in the atmosphere) to the extent that retrieved values no longer realistically represent actual extinction profiles. When the surface albedo is fixed in retrievals with GOME-2A spectra, convergence deteriorates as expected, but retrieved aerosol layer pressures become much higher (i.e., layer lower in atmosphere). The comparison with lidar measurements indicates that retrieved aerosol layer heights are indeed representative of the underlying profile in that case. Finally, subsequent retrieval simulations with two-layer aerosol profiles show that a model error in the assumed profile (two layers in the simulation but only one in the retrieval) is partly absorbed by the surface albedo when this parameter is fitted. This is expected in view of the correlations between errors in fit parameters and the effect is relatively small for elevated layers (less than 100 hPa). If one of the scattering layers is near the surface (boundary layer aerosols), the effect becomes surprisingly large, in such a way that the retrieved height of the single layer is above the two-layer profile. Furthermore, we find that the retrieval solution, once retrieval converges, hardly depends on the starting values for the fit. Sensitivity experiments with GOME-2A spectra also show that aerosol layer height is indeed relatively robust against inaccuracies in the assumed aerosol model, even when the surface albedo is not fitted. We show spectral fit residuals, which can be used for further investigations. Fit residuals may be partly explained by spectroscopic uncertainties, which is suggested by an experiment showing the improvement of convergence when the absorption cross section is scaled in agreement with Butz et al. (2013) and Crisp et al. (2012), and a temperature offset to the a priori ECMWF temperature profile is fitted. Retrieved temperature offsets are always negative and quite large (ranging between −4 and −8 K), which is not expected if temperature offsets absorb remaining inaccuracies in meteorological data. Other sensitivity experiments investigate fitting of stray light and fluorescence emissions. We find negative radiance offsets and negative fluorescence emissions, also for non-vegetated areas, but from the results it is not clear whether fitting these parameters improves the retrieval. Based on the present results, the operational baseline for the Aerosol Layer Height product currently will not fit the surface albedo. The product will be particularly suited for elevated, optically thick aerosol layers. In addition to its scientific value in climate research, anticipated applications of the product for TROPOMI are providing aerosol height information for aviation safety and improving interpretation of the Absorbing Aerosol Index.

TROPOMI’s Aerosol Layer Height algorithm currently assumes a simplified aerosol profile in the form of a single layer of homogeneously distributed aerosols. The height of this layer is retrieved by using height information from the O2 A band. It is not straightforward to interpret the retrieved height parameter, since true aerosol profiles are typically complex and heterogeneous. We used radiative transfer theory to better understand the retrieved parameter. In addition to an available multiple scattering description of the radiation field, a single scattering approximation was developed as well. Comparing the single scattering approximation to the full multiple scattering radiative transfer revealed that the approximation is accurate inside strong absorption parts of the O2 A band for realistic aerosol profiles. Retrieval simulations for realistic aerosol scenes suggested that the retrieved height parameter can be interpreted as a centroid of the aerosol profile, if the surface albedo is not fitted. The retrieved height parameter was compared to three different centroids of the aerosol extinction profile, which are constructed using weighted averages. Two of these methods take into account the sensitivity of the measured top of atmosphere radiance with respect to aerosol at different altitudes. This sensitivity was obtained by taking a directional derivative of a functional, which maps the aerosol extinction profile to a measured top of atmosphere radiance. This yields semi-analytic derivatives. The two methods differ in the way the derivatives are determined. The first uses a multiple scattering description and the other uses the single scattering approximation. All centroid methods showed good agreement with the retrieved height parameter. In additional retrieval experiments we also fitted the surface albedo. These experiments showed that, as soon as the standard error of the surface albedo exceeds 10−3, a bifurcation occurs, which results in unrealistic results. These unrealistic results can no longer be interpreted as centroids of aerosol extinction profiles.

The aim of this work is to investigate whether or not both the cis and the trans isomers of either 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and 1,4-diaminocyclohexane (1,4-DACH) are participating in the formation of cryst. domains in copolyamides based thereon. Two isomeric series of partially cycloaliph. copolyamides were synthesized. In the series based on polyamide 12.6, the adipic acid residues were partially replaced by cis/trans mixts. of 1,4-CHDA, and in the series based on polyamide 4.14, the 1,4-diaminobutane residues were partially replaced by cis/trans mixts. of 1,4-DACH. By submitting these series of copolyamides to careful DSC and WAXS analyses, it could unambiguously be concluded that only the trans isomers of both 1,4-CHDA and 1,4-DACH residues are cocrystg. with the adipic acid based residues. Such evidence was not yet available in literature.

Two series of isomeric copolyamides were synthesised, viz. polyamides 12.6 for which the adipic acid residues were partially replaced by cis/trans-1,4-cyclohexanedicarboxylic acid (1,4-CHDA), and polyamides 4.14 for which the 1,4-diaminobutane residues were partially replaced by cis/trans-1,4-diaminocyclohexane (1,4-DACH). A careful DSC and WAXS analysis learned that only the trans isomers of both 1,4-DACH and 1,4-CHDA are incorporated into the crystalline phase. During DSC analysis, an intitial high trans content is preserved in the case of the non-isomerising 1,4-DACH, whereas the 1,4-CHDA residues gradually isomerise from a high initial trans content to a significanly lower trans content. Since these cis residues are not incorporated into the crystalline domains, the lower second heating melting points of the 1,4-CHDA-based copolyamides in comparison with 1,4-DACH-based copolyamides, having similar cycloaliphatic monomer contents, can be understood.

A series of new poly(ether-ester-imide)s, PEEIs, was prepared from an imide dicarboxylic acid based on 1,4-diaminobutane and trimellitic anhydride. This imide dicarboxylic acid polycondensed with 1,4-dihydroxybutane formed the hard segments and poly(ethylene oxide), PEO-1000, or mixtures of PEO-1000 and poly(tetramethylene oxide), PTMO-1000, were used as soft segments. Whenever PTMO-1000 was used as comonomer, macrophase separation was observed at the end of the polycondensation. However, this macrophase separation had little influence on the mechanical properties. A poly(ether-esterimide), PEEI, containing neat PEO-1000 was characterized by dynamic mechanical thermoanalysis, stress-strain and hysteresis measurements, and by melt rheology. The mechanical properties were compared with those of an analogous PEEI containing neat PTMO-1000 and with those of a poly(etherester), PEE, based on poly(butylene terephthalate) hard segments and PTMO-1000.

An imide dicarboxylic acid was prepared from 1,6-diaminohexane and trimellitic anhydride and esterified with ethanol. This imide monomer was polycondensed with three different poly(tetramethylene oxide) diols (PTMO-650, PTMO-1000 and PTMO-2000) and with an excess of 1,4-dihydroxybutane. When PTMO-1000 was used, and even more when PTMO-2000 was used, a partial macrophase separation occurred at the end of the polycondensation process. The resulting poly(ether-ester-imide)s (PEEIs) were characterized by IR and 1H NMR spectroscopy, by viscosity and DSC measurements. Compared to thermoplastic elastomers based on poly(butylene terephthalate) these PEEIs crystallize slowly. Selected PEEIs were also characterized by dynamic melt rheology, by dynamic mechanical thermoanalysis, by stress–strain and by hysteresis measurements.

Starting from 1,4-diaminobutane and trimellitic anhydride a bisimide dicarboxylic acid was prepared which was transformed into its diethyl ester. This imide monomer was polycondensed with mixtures of 1,4-dihydroxybutane and poly(tetramethylene oxide) (PTMO) diols having number average molecular weights (Mns) of 650, 1000 or 2000Da. For each PTMO diol, the weight fraction of the hard segments was varied from 30 over 40 and 50–60%. For the PTMO diols 1000 and 2000, macrophase separation was observed during polycondensation. This problem was solved in the case of PTMO-1000 by a PTMO diol of greater polydispersity. The chemical structure of the poly(ether-ester-imide)s, PEEIs, was characterized by IR and 1H NMR spectroscopy. The phase transitions were identified by DSC and DMTA measurements, which revealed that all members of this series were slowly crystallizing materials. The mechanical properties were determined by stress–strain and hysteresis measurements. Macrophase separation during the polycondensation was reflected in poorer mechanical properties.

Starting from 1,4-diaminobutane and trimellitic anhydride, alpha,omega-diaminobutanebis(trimellitimide) was synthesized and subsequently esterified with methanol. Thermal polycondensation with dimethyl terephthalate in mol ratios from 0 to 100% and 1,4-butanediol yielded the corresponding series of random copoly(ester imide)s based on poly(butylene terephthalate) (PET). Differential scanning calorimetry and wide-angle x-ray scattering showed that all poly(ester imide)s are semicrystalline with degrees of crystallinity up to 50% (depending on the comonomer content). Compared to pure PET, the rate of crystallization, however, is strongly decreased if the content of the comonomer is higher than 20%. Annealing is necessary to crystallize these materials. The melting temperatures (T(m)s) of the copoly(ester imide)s display the usual melting point depression of copolymers: by increasing the content of the comonomer, the melting temperatures initially decrease but increase when the content of the comonomer is increased further. The glass transition temperatures (T(g)s) increase linearly with increasing content of the comonomer. The maximum T-m(258 degrees C) and the maximum T-g(100 degrees C) were obtained for the homopoly(ester imide) derived from N,N'-butane-alpha,omega-diyl-bis(trimellitimide) and 1,4-butanediol. Some mechanical properties were determined on injection-molded testbars of three poly(ester imide)s containing various amounts of N,N'-butane,alpha,omega-diyl-bis(trimellitimide). They were compared to those of pure PET and poly(ethylene terephthalate).

Primary amine terminated polystyrene (PS-NH2), with Mn=12,000 g/mole and Mw=23,000 g/mole, is applied as a reactive compatibilizer for poly(styrene-co-maleic anhydride)/ poly(phenylene oxide) (SMA/PPO) blends, The continuous SMA phase is impact modified by ABS, whereas the dispersed PPO phase contains SEBS as an impact modifier. The addition of 10 wt % of the reactive PS-NH2 compatibilizer to a SMA/ABS/PPO/SEBS 30/30/30/10 blend results in a finer blend morphology than 10 % of a commercially available, bulky PS-g-PMMA graftcopolymer with Mn=45,300 and Mw=293,400 g/mole. In addition, PS-NH2 gives a more pronounced enhancement of the yield stress, the stress at break and the notched Izod impact than the graftcopolymer. On the other hand, the elongation at break is higher in the case of the nonreactive PS-g-PMMA. It is demonstrated that the lower elongation al break for the PS-NH2 based blends can be ascribed to surface imperfections, probably introduced by an observed strongly elastic character due to partial crosslinking of the SMA/ABS phase by difunctional H2N-PS-NH2.

Primary amine terminated polystyrene (PS-NH2), with <(M)over bar n> = 12,000 g/mol and <(M)over bar w> = 23,000 g/mol, was applied as a reactive compatibilizer for poly(styrene-co-maleic anhydride)/ poly(phenylene oxide) (SMA/PPO) blends, in which both an impact modifier for the continuous SMA phase, viz. ABS, and the dispersed PPO phase, viz. SEES, was incorporated. During melt blending, SMA-g-PS copolymers are generated at the interface between the SMA/ABS and the PPO/SEBS phases. The addition of 10 wt % of the reactive PS-NH2 compatibilizer to a SMA/ABS/PPO/SEBS 30/30/30/10 blend results in a more significant refinement of the dispersed PPO/SEBS particles than 10 wt % of a commercially available, bulky PS-graft-PMMA copolymer with <(M)over bar n> = 45,300 and <(M)over bar w> = 293,400 g/mol. In addition, PS-NH2 gives a more pronounced enhancement of the yield stress, the stress at break and the notched Izod impact than the PS-g-PMMA. On the other hand, the elongation at break is higher in the case of the non-reactive PS-g-PMMA. It was demonstrated that surface imperfections, probably introduced by an observed strongly elastic character due to partial crosslinking of the SMA/ABS phase by difunctional H2N-PS-NH2, are responsible for the lower elongation at break for the PS-NH2 based blends.

The synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)(2)(PS)(7.5)(DMAP)(2.5)Cl]Cl, where bipy = 2, 2'-bipyridyl, PS = polystyrene, and DMAP = poly[4-(N-methyl-N-p-vinylbenzylamino) pyridine], are described. The charge transport properties of electrodes modified with the redox material are investigated using cyclic voltammetry and chronoamperometry. The modified electrode behaves as an efficient electrocatalyst for the outer-sphere reduction of Fe-III, with the cross-exchange reaction occurring at the surface of the polymer (Sk'') at concentrations less than 1.0 x 10(-3) mol dm(-3) Fe-III, with a change over to the St(e) kinetic regime at higher substrate concentrations. Direct agreement was observed between the kinetic behavior at rotating disk electrodes and in thin-layer flow cells. Application of the modified electrodes for the determination of iron in pharmaceutical formulations and the long term stability of the electrodes are investigated. The results obtained are compared with those reported for the analogous metallopolymer [Os(bipy)(2)(PVP)(10)Cl]Cl, where PVP is poly-4-vinylpyridine.

The compatibilization and impact modification of blends of a relatively new engineering plastic polyamide 4.6 (PA 4.6) and a poly(aryl ether sulfone) (PSU) are investigated. PSU-b-PA6 block copolymers, which can be easily synthesized by ring opening polymerization of epsilon-caprolactam in the presence of a commercial PSU, were found to be very efficient emulsifiers for these incompatible blends. Small amounts (1-4%) of copolymer are sufficient to significantly reduce the particle size and to improve the tensile and impact properties. Combinations of the copolymer and an impact modifier (ethylene-propylene rubber grafted with maleic anhydride) are synergistic and high impact PSU/PA 4.6 alloys are obtained in that way.

Gel-spun filaments of different initial morphologies have been subjected to controlled drawing at elevated temperatures. The drawn samples have been examined by high-resolution scanning electron microscopy. The deformation mechanism at temperatures up to 120° C is very similar to crazing, especially in the case of unoriented gel-spun filaments. Filaments exhibiting a shish-kebab morphology offer the opportunity of examining the deformation of elementary fibrils in a quantitative way. The transformation of individual lamellae into fibrils is the initial deformation mode, which is followed by slip of fibrils at a later stage. This is concluded from a comparison of experimental data and model calculations of the maximum draw ratio. Drawing at 144° C results in the formation of globular aggregates of lamellae, with a characteristic long period of 40 nm. This long period persists until all the globules have been converted, by micronecking, into aggregate fibrils of extended-chain character. On a molecular scale, the various processes can be described as the temperature-dependent flow behaviour of an entanglement network.

Polyethylene mats of shish-kebab fibrils were prepared from solution by stirring-induced crystallization, and subjected to deformation. A morphological study by scanning electron microscopy showed that the elementary shish-kebabs are elongated during drawing. For low draw ratios, the average distance between the lamellae on the fibrils increases proportionally to the draw ratio. The invariance of the fibril diameter upon drawing indicates a transformation of lamellar into fibrillar material. The molecular topology which underlies this deformation mode is discussed and related to the crystallization process.

Copolymers of styrene and 4-vinylpyridine have been utilized as macromolecular ligands for copper. The intrinsic activities of unbound and anchored macromolecular copper catalysts were identical in the oxidative coupling reaction of 2,6-di-t-butylphenol. Anchorage to silica resulted in a decrease of the equilibrium constant for substrate complexation because of water enrichment around the non-porous silica spheres. This effect could be suppressed by silanization of the silica support, and after such treatment higher substrate complexation equilibrium constants were observed than for unbound macromolecular catalysts. However, partial adsorption of the macromolecular ligands on to the silanized silica support occurred, leading to deactivation of catalytically active sites. This adsorption was strongly influenced by the nature of the silica surface and by the polarity of the comonomer, e.g. styrene or methyl methacrylate, in the macromolecular amine.