Climate simulations for 1880-2003 with GISS modelE

We carry out climate simulations for 1880-2003 with GISS modelE driven by ten measured or estimated climate forcings. An ensemble of climate model runs is carried out for each forcing acting individually and for all forcing mechanisms acting together. We compare side-by-side simulated climate change for each forcing, all forcings, observations, unforced variability among model ensemble members, and, if available, observed variability. Discrepancies between observations and simulations with all forcings are due to model deficiencies, inaccurate or incomplete forcings, and imperfect observations. Although there are notable discrepancies between model and observations, the fidelity is sufficient to encourage use of the model for simulations of future climate change. By using a fixed well-documented model and accurately defining the 1880-2003 forcings, we aim to provide a benchmark against which the effect of improvements in the model, climate forcings, and observations can be tested. Principal model deficiencies include unrealistically weak tropical El Nino-like variability and a poor distribution of sea ice, with too much sea ice in the Northern Hemisphere and too little in the Southern Hemisphere. The greatest uncertainties in the forcings are the temporal and spatial variations of anthropogenic aerosols and their indirect effects on clouds.Comment: 44 pages; 19 figures; Final text accepted by Climate Dynamic

ENDOGLIN is dispensable for vasculogenesis, but required for vascular endothelial growth factor-induced angiogenesis

ENDOGLIN (ENG) is a co-receptor for transforming growth factor-β (TGF-β) family members that is highly expressed in endothelial cells and has a critical function in the development of the vascular system. Mutations in Eng are associated with the vascular disease known as hereditary hemorrhagic telangiectasia type l. Using mouse embryonic stem cells we observed that angiogenic factors, including vascular endothelial growth factor (VEGF), induce vasculogenesis in embryoid bodies even when Eng deficient cells or cells depleted of Eng using shRNA are used. However, ENG is required for the stem cell-derived endothelial cells to organize effectively into tubular structures. Consistent with this finding, fetal metatarsals isolated from E17.5 Eng heterozygous mouse embryos showed reduced VEGF-induced vascular network formation. Moreover, shRNA-mediated depletion and pharmacological inhibition of ENG in human umbilical vein cells mitigated VEGF-induced angiogenesis. In summary, we demonstrate that ENG is required for efficient VEGF-induced angiogenesis

Fate of products of degradation processes: consequences for climatic change.

The end products of atmospheric degradation are not only CO2 and H2O but also sulfate and nitrate depending on the chemical composition of the substances which are subject to degradation processes. Atmospheric degradation has thus a direct influence on the radiative balance of the earth not only due to formation of greenhouse gases but also of aerosols. Aerosols of a diameter of 0.1 to 2 micrometer, reflect short wave sunlight very efficiently leading to a radiative forcing which is estimated to be about -0.8 watt per m2 by IPCC. Aerosols also influence the radiative balance by way of cloud formation. If more aerosols are present, clouds are formed with more and smaller droplets and these clouds have a higher albedo and are more stable compared to clouds with larger droplets. Not only sulfate, but also nitrate and polar organic compounds, formed as intermediates in degradation processes, contribute to this direct and indirect aerosol effect. Estimates for the Netherlands indicate a direct effect of -4 watt m-2 and an indirect effect of as large as -5 watt m-2. About one third is caused by sulfates, one third by nitrates and last third by polar organic compounds. This large radiative forcing is obviously non-uniform and depends on local conditions

Aerosol; Cyclus en Invloed op de Stralingsbalans MEting en MOdellering van de reductie van straling bij aerosolen

De drijvende kracht in de door de mens veroorzaakte klimaatverandering is de verandering in de stralingsbalans. Deze wordt niet alleen beinvloed door de broeikasgassen maar ook door aerosolen (fijne in lucht zwevende deeltjes). De aerosolen worden ook door de mens gemaakt, vooral via fossiele verbranding. Aerosolen kaatsen een deel van het zonlicht terug. Dit leidt tot een verminderde instraling. Het aerosol-effect van door de mens gegenereerde aerosolen werkt dus precies omgekeerd aan het 'normale' broeikaseffect van de gassen die de langgolvige aardse uitstraling tegenhouden. Door verminderde instraling warmt de aarde minder op. De invloed van de antropogene aerosolen is groot: De extra door de mens geproduceerde broeikasgassen geven een verandering in de stralingsbalans van ongeveer 2.5W m-2, volgens IPCC. De geschatte tegengestelde bijdrage van door de mens gemaakte aerosol deeltjes is, als mondiaal gemiddelde -0.8 W m-2, maar met een onzekerheid van minstens een factor twee. De onzekerheid in de verstoring van de stralingsbalans ('forcering') door aerosolen vormt momenteel een van de grootste onzekerheden in de klimaatforcering over de industriele periode.Anthropogenic aerosols reflect solar radiation and therefore act as cooling agents. The perturbation ('forcing') of the radiation balance is so large that, according to estimates by IPCC, it could off-set the longwave radiative forcing by the man-made greenhouse gases in areas like Europe. IPCC reports the uncertainty in the globally averaged aerosol forcing to be in the order of 3 W M-2. This uncertainty exceeds the magnitude of longwave forcing by the man-made greenhouse gases. Of national interest is the local/regional nature of aerosol forcing, which is due to the limited residence time of aerosols in the atmosphere. The claim by IPCC that sulphate is the only relevant man-made aerosol component is highly questionable for Europe. Whereas the value of the aerosol effect is so uncertain, predictions of the coming trend are even more problematic. This is due to the fact that the most important anthropogenic ingredients of the aerosol are not directly emitted, but made in the atmosphere. A one-to-one relationship between the emission of the precursors and resulting aerosol seems rather unlikely given a non-linear historical trend. Therefore only a combined approach in which aerosol fields are modelled, and modelled fields, together with the calculated reduction in solar flux, should be tested. This approach should provide the tools to perform, with sufficient confidence, scenario calculation for the aerosol effect. This report shows some of the attempts to improve the current large uncertainty in forcing of the radiation balance by anthropogenic aerosol (in Europe) by a combined experimental/modelling program. This is achieved by assessment of the major aerosol components involved and there sources, using detailed measurements in The Netherlands as a reference for model input and output.SG-NO

A high-flow humidograph for testing the water uptake by ambient aerosol

A ``humidograph{''} with an air flow rate of 0.4 m(3) s(-1) was built to investigate the uptake of water and its effect on sizing, collection and light scattering of ambient aerosol. In the humidograph the relative humidity (RH) can be scanned over a large RH trajectory. Its performance was assessed with laboratory particles of ammonium nitrate, ammonium sulfate and sodium chloride that are the major hygroscopic components of ambient aerosol. The increase in size at the deliquescence points, which ideally is a stepwise function of RH, occurs over a range of 3\% RH units. This is shown to be an optimum value in a system of such large dimensions. Because the vapor pressure of ammonium nitrate increases significantly with temperature, its evaporative loss was investigated as a function of heating/drying temperature. The loss of pure test aerosol, with a mass distribution similar to that in the ambient atmosphere, was found to be acceptable for drying temperatures of up to 40 degrees C. The sizing of deliquesced aerosol by LAS-X monitors was tested and found to be a complex function of RH. In Berner low-pressure impactors growth of hygroscopic aerosol was not observed, not even at an RH approaching saturation. (C) 2000 Elsevier Science Ltd. All rights reserved

Comparability of three spectrometers for monitoring urban aerosol

The comparability was tested of three aerosol ``spectrometers{''}, used in a program for monitoring the spectra of fine and ultrafine particles in three European cities. Droplets of sebacate, solid ammonium sulfate and agglomerates of elemental carbon were used in the tests, representing the major chemical and structural types of particles encountered in urban aerosol. Particles in the ultrafine range (10-100 nm) are sized by electrical mobility (SMPS, DMPS and EAS) and the ``spectrometers{''} gave very similar size distributions for these aerosols. The integrated number concentrations were on average within 20\% of the directly measured total number concentrations. Particles with a size between 0.1 and 2.5 mum, in which most of the volume/mass is concentrated, are being differently classified in the three ``spectrometers{''}, respectively, with a low- and a high-flow LAS-X, and field charging in the EAS. The agreement between the three instruments in this size range was less good, which was partly caused by signal overload in the high-flow optical sizer, which was solved using a larger threshold. A complication occurred with the elemental carbon, which was composed of highly agglomerated entities. Particles, sized by the mobility instrumentation as being in the range of 100-400 nm, were not detected by the optical sizers. Volume (spectra) for ammonium sulfate deduced from the number spectra were compared with the mass (spectra) obtained with cascade impacters. The comparison was good for the LAS-Xs; the EAS overestimated volume/mass. (C) 2001 Elsevier Science Ltd. All rights reserved

De effecten van aerosolen op de kortgolvige stralingsbalans

IPPC reports the aerosol radiative forcing per major aerosol category, like sulphate and fossil fuel derived carbon. Part of this carbon is reflective and part of the material (black carbon "soot") absorbs radiation. We find that in the Netherlands sulphate contributes some 30% to the reflection. Nitrate contributes even more; an estimated 35%. The local importance of nitrate is acknowledged in the new IPCC-TAR, but it is stated that insufficient data exist to assess its importance outside of the Netherlands. The amount of "fossil fuel" carbon could not be directly quantified. The reason is that it consists of thousands of different chemical compounds that all have different physicochemical properties. However, by deduction we found that its concentration is substantial. The mentioned three components, nitrate, sulphate and carbon, are thus the dominant aerosol components in the regional aerosol radiative forcing. As can be seen in the results, the forcing on partly cloudy days seems less because of a shorter sunshine duration. It should then be considered that on cloudy days the reflective power of the aerosol is higher due to the higher relative humidity and the associated uptake of water by the aerosol. This compensates for the shorter sunshine duration. Reflection of solar radiation caused by the aerosol is exerted by aerosol components that can be of a natural origin or produced by man. In our report we show, on the basis of the aerosol composition, that at least 85% of the aerosol is of a manmade origin and the aerosol reflection is therefore a forcing. The forcing is defined as the amount of solar radiation reflected back into space, and not available for heating of the earth due to the presence of manmade aerosol.SG-NO

The continuous analysis of nitrate and ammonium in aerosols by the steam jet aerosol collector (SJAC): extension and validation of the methodology

Classical methodology based on the application of filters for sampling, followed by extraction and analysis, introduces severe artifacts for semi-volatile compounds like ammonium nitrate. These filter methods do not meet the requirements for the assessment of the impact of aerosols on acidification, air quality and especially on the radiative balance, in terms of required speed, detection limits and selectivity. These artifacts are avoided by using a steam jet aerosol collector sampler, based on scavenging of aerosols by droplet formation, in combination with on-line analytical techniques such as ion-chromatography for nitrate and membrane separation followed by conductivity detection for ammonium. The SJAC sampler combines very low blanks with high efficiency of collection of particles. The ammonium detector and the IC system, based on 1-point internal standard calibration in combination with correction for curved calibration graphs, enables detection of ammonium and nitrate at background conditions, the detection limit is about 0.02 mug m(-3) of ammonium and nitrate. Accuracy is, depending on ambient concentration, in the order of 5-10\% relative, at a range of 0.05-50 mug m(-3). The: time resolution is 15-120min, depending on required detection limit, and is short enough for continuously monitoring the chemical composition of aerosols. Quality assurance and quality control experiments and intercomparison experiments with classical filter methods, thermo-denuder systems, denuder difference methods and other continuous monitoring techniques have shown that the results are reliable. The instrument has successfully been employed in field campaigns in Europe and the US. (C) 2001 Elsevier Science Ltd. All rights reserved