Two-dimensional distributions of sulfur compounds in the troposphere: Implications for the atmospheric sulfur budget

Summary We have built a two-dimensional model of the lower atmosphere extending from pole to pole and from the ground to about 20 km. Meridional circulation is obtained from observational data of vertical velocity and is made self-consistent for the meridional velocity through the use of the continuity equation. Eddy processes are parameterized in terms of eddy diffusion coefficients. Results are reported for OCS, CS₂, H₂S, CH₃SCH₃, SO₂ and compared both with available experimental data and other similar calculations. Our results show a general agreement with both concentrations and fluxes. Production of SO₂ takes into account both natural and anthropogenic sources. An interesting result is found for OCS which seems to have a net chemical production in the troposphere. A possible role of OCS as a stratospheric sulphur source should be reconsidered. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Light scattering by helical fiber structures: Experimental models

Samples of two helically wound monofilaments were used as experimental models to check the theoretical expression for light scattering from helixes. A method of estimating the pitch and tilt of the helixes was outlined and the results were compared with measurements from microscopy. The agreement was satisfactory. Layer line streaking and splitting was observed and explained in terms of irregularity of the helical parameters. Samples of several helically wound monofilaments were also prepared and their scattering patterns were compared with those from native and regenerated cellulosic fibers.     

Thermal structure and relaxation rates of the perturbed atmosphere: a study with a photochemial radiative convective model

Summary We have developed a radiative-photochemical model to evaluate the temperature distribution in the Earth's atmosphere between the ground and 70 km. The model takes into account the interaction between photochemistry and temperature. We report results of a number of experiments performed with this model to assess the climatic effects of varying the ozone distribution and the ozone overburden. An evaluation of the relaxation rates of both ozone and temperature is also reported. In particular, the importance of the ozone distribution with respect to the ?greenhouse effect? is further investigated.

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Riassunto è stato sviluppato un modello fotochimico-radiativo-convettivo dell'atmosfera terrestre per calcolare la distribuzione di temperatura fra la superficie e 70 km. Il modello tiene conto dell'interazione fra fotochimica e temperature. Si riportano i risultati di alcuni esperimenti effettuati con il modello atti a studiare gli effetti climatici dovuti alle variazioni del carico e distribuzione di ozono. Si riporta anche una valutazione dei tempi di rilassamento per l'ozono e la temperatura. Inoltre è ulteriormente studiata l'influenza della distribuzione di ozono sull'effetto serra.

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Резюме Мы развиваем радиационную-фотохимическую модель ддя оценки распределения температур в атмосфере земли от поверхности до 70 км. Модель учитывает взаимодействие между фотохимией и температурой. Мы приводим результаты ряда чэкспериментов, выполненных с помощьу предложенной модели для оценки климатических эффектов изменения распределения озона. Проводится оценка интенсивностей релаксации распределений озона и температуры. В частности, исследуется важность распределения озона.

     

Monoclonal antibody based electrochemical immunosensor for the determination of ochratoxin A in wheat

Competitive electrochemical enzyme-linked immunosorbent assays based on disposable screen-printed electrodes have been developed for quantitative determination of ochratoxin A (OTA). The assays were carried out using monoclonal antibodies in the direct and indirect format. OTA working range, I₅₀ and detection limits were 0.05-2.5 and 0.1-7.5 μg L⁻¹, 0.35 (±0.04) μg L⁻¹ and 0.9 (±0.1) μg L⁻¹, 60 and 100 μg L⁻¹ in the direct and indirect assay format, respectively. The immunosensor in the direct format was selected for the determination of OTA in wheat. Samples were extracted with aqueous acetonitrile and the extract analyzed directly by the assay without clean-up. The I₅₀ in real samples was 0.2 μg L⁻¹ corresponding to 1.6 μg/kg in the wheat sample with a detection limit of 0.4 μg/kg (calculated as blank signal −3σ). Within- and between-assay variability were less than 5 and 10%, respectively. A good correlation (r = 0.9992) was found by comparative analysis of naturally contaminated wheat samples using this assay and an HPLC/immunoaffinity clean-up method based on the AOAC Official Method 2000.03 for the determination of OTA in barley.     

Differential-pulse polarography of trichothecene mycotoxins : Determination of Deoxynivalenol,Nivalenol and Fusarenone-X in Maize

The polarographic behaviour of representative trichothecenes is described. Compounds characterized by an α,β-unsaturated carbonyl group or by a macrocyclic lactonic ring were found to be electroactive in a methanolic Britton—Robinson buffer. Differential pulse polarography provides detection limits of the order of 40 nmol l^?1 with linear ranges extending up to 9 μmol l^?1. The application of differential pulse polarography is described for the determination of nivalenol (3α, 4β, 7α, 15-tetrahydroxy-12,13-epoxytrichotec-9-en-8-one), deoxynivalenol (3α, 7α, 15-trihydroxy-12,13-epoxytrichothec-9-en-8-one) and fusarenone-X (3α, 7α, 15-trihydroxy-4 β-acetoxy-12,13-epoxytrichothec-9-en-8-one) in infected maize. A suitable liquid/liquid extraction and chromatographic cleanup procedure is reported. Detection limits for the overall procedure and for a sample size of 50 g are of the order of 50 ng g^?1 while average recoveries range from 20 to 70% at the 1 μg g^?1 level. Polarographic results are compared with those obtained by a gas-chromatographic method.     

Ground-based monitoring of pinatubo aerosols and ozone at L''Aquila, Italy I.—Evidences for ozone depletion during 1991/92 winter months

Summary Possible evidence for stratospheric ozone depletion at northern midlatitudes as a consequence of the Pinatubo aerosol cloud is presented in this work. A ten-month record of aerosol and ozone measurements taken at the lidar station of L'Aquila, Italy, is compared to the 1985–1986 SBUV and SAGE II ozone data. Ozonesonde data collected in the station of Hohenpeissenberg, Germany, and S. Pietro Capofiume, Italy, are used to validate the DIAL measurements corrected for the aerosol presence.     

Heterometallic modular metal-organic 3D frameworks assembled via new tris-β-diketonate metalloligands: nanoporous materials for anion exchange and scaffolding of selected anionic guests

The modular engineering of heterometallic nanoporous metal-organic frameworks (MOFs) based on novel tris-chelate metalloligands, prepared using the functionalised β-diketone 1,3-bis(4'-cyanophenyl)-1,3-propanedione (HL), is described. The complexes [M(III)L(3)] (M=Fe(3+), Co(3+)) and [M(II)L(3)](NEt(4)) (M=Mn(2+), Co(2+), Zn(2+), Cd(2+)) have been synthesised and characterised, all of which exhibit a distorted octahedral chiral structure. The presence of six exo-oriented cyano donor groups on each complex makes it a suitable building block for networking through interactions with external metal ions. We have prepared two families of MOFs by reacting the metalloligands [M(III)L(3)] and [M(II)L(3)](-) with many silver salts AgX (X=NO(3)(-), BF(4)(-), PF(6)(-), AsF(6)(-), SbF(6)(-), CF(3)SO(3)(-), tosylate), specifically the [M(III)L(3)Ag(3)]X(3)·Solv and [M(II)L(3)Ag(3)]X(2)·Solv network species. Very interestingly, all of these network species exhibit the same type of 3D structure and crystallise in the same trigonal space group with similar cell parameters, in spite of the different metal ions, ionic charges and X(-) counteranions of the silver salts. We have also succeeded in synthesising trimetallic species such as [Zn(x)Fe(y)L(3)Ag(3)](ClO(4))((2x+3y))·Solv and [Zn(x)Cd(y)L(3)Ag(3)](ClO(4))(2)·Solv (with x+y=1). All of the frameworks can be described as sixfold interpenetrated pcu nets, considering the Ag(+) ions as simple digonal spacers. Each individual net is homochiral, containing only Δ or Λ nodes; the whole array contains three nets of type Δ and three nets of type Λ. Otherwise, taking into account the presence of weak Ag-C σ bonds involving the central carbon atoms of the β-diketonate ligands of adjacent nets, the six interpenetrating pcu networks are joined into a unique non-interpenetrated six-connected frame with the rare acs topology. The networks contain large parallel channels of approximate hexagonal-shaped sections that represent 37-48% of the cell volume and include the anions and many guest solvent molecules. The guest solvent molecules can be reversibly removed by thermal activation with retention of the framework structure, which proved to be stable up to about 270°C, as confirmed by TGA and powder XRD monitoring. The anions could be easily exchanged in single-crystal to single-crystal processes, thereby allowing the insertion of selected anions into the framework channels.     

Liquid chromatographic determination of Alternaria toxins in carrots

A liquid chromatographic (LC) method was developed for the determination of Alternaria radicina and A. alternata toxins in carrots. Toxins were extracted from carrot with an acidified mixture of water-methanol-acetonitrile. The filtered extract was divided in 2 parts that were purified by solid-phase extraction on a C18 column for the analysis of radicinin (RAD), altertoxin-I (ATX-I), alternariol (AOH), and alternariol methyl ether (AME), and on a polymeric Oasis HLB column for tenuazonic acid (TeA). Toxins were quantified by reversed-phase LC with UV diode array detection by using 2 consecutive isocratic mixtures of acetonitrile-sodium dihydrogen phosphate solution. Mean recoveries of TeA, ATX-I, AME, RAD, and AOH from carrots spiked at levels between 0.5 and 3.0 microg/g were 69, 71, 90, 36, and 78%, with mean within-laboratory repeatability of 14, 5, 4, 6, and 18%, respectively. The mean between-laboratory reproducibilities for the determination of TeA, ATX-I, AME, and RAD in spiked samples were 25, 22, 6, and 12%, respectively. Limits of detection (signal-to-noise ratio of 3) for RAD, TeA, ATX-I, AME, and AOH were 0.006, 0.02, 0.02, 0.01, and 0.005 microg/g, respectively. RAD was detected (0.16-13.9 microg/g) in 3 out of 266 carrot samples produced under organic conditions in 3 European locations, whereas A. alternata mycotoxins were not found in any tested samples.     

Analysis of T-2 and HT-2 toxins in cereal grains by immunoaffinity clean-up and liquid chromatography with fluorescence detection

A sensitive, precise and accurate method has been developed for the simultaneous determination of T-2 and HT-2 toxins in cereal grains at ppb levels using high-performance liquid chromatography (HPLC) with fluorescence detection and 1-antroylnitrile (1-AN) as labeling reagent after immunoaffinity clean-up. Cereal samples were extracted with methanol/water (90:10, v/v), and the extracts were cleaned-up through commercially available immunoaffinity columns containing monoclonal anti-T-2 antibodies (T-2 test HPLC, Vicam). T-2 and HT-2 toxins were quantified by reversed-phase HPLC with fluorometric detection (excitation wavelength 381 nm, emission wavelength 470 nm) after derivatization with 1-AN. The monoclonal antibody showed 100% cross-reactivity with both T-2 and HT-2 toxin, and the immunoaffinity column clean-up was effective up to 1.4 microg of both toxins. The method was successfully applied to the analysis of T-2 and HT-2 toxins in wheat, maize and barley. Recoveries from spiked samples with toxin levels from 25 to 500 microg/kg ranged from 70% to 100%, with relative standard deviation generally lower than 8%. The limit of detection of the method was 5 microg/kg for T-2 toxin and 3 microg/kg for HT-2 toxin, based on a signal-to-noise ratio 3:1. HT-2 toxin was detected in ten naturally contaminated wheat samples out of 14 samples analyzed, with toxin levels ranging from 10 to 71 microg/kg; three of them contained also T-2 toxin up to 12 microg/kg.