Browsing by Author "ten Brink, HM"
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Item Open Access A high-flow turbulent cloud chamber(AEROSOL SCIENCE AND TECHNOLOGY, 1996) Khlystou, A; Kos, GPA; ten Brink, HMA large laboratory facility (cloud chamber) has been built to study cloud formation under reproducible conditions. The chamber was designed to assess the influence of anthropogenic aerosols on the microstructure of marine clouds in coastal Western Europe. For this reason the supersaturations in the chamber are low, in the order of 0.1\%, typical for coastal marine stratus. The very large size (30 m(3)) and flow (30 m(3)/min) of the chamber allow unperturbed use of conventional cloud instrumentation like Forward Scattering Spectrometer Probe (TSI Inc.) and high-flow cascade impactors for chemical analysis of aerosol and droplets. The performance of the cloud chamber was tested with laboratory-generated submicron-sized ammonium sulphate aerosol with a lognormal size distribution and varying the number concentrations. It was found that the sulphate particles above a threshold size of 0.07 or 0.1 mu m in diameter (dependent on the settings) grew into droplets (became `'activated''), which corresponds according to the Kohler theory to supersaturations of 0.26\% and 0.15\%, respectively. Estimates of the supersaturation in the chamber from the measured liquid water content (LWC) gave the same value. Tests showed that LWC, droplet spectra, and activation threshold were stable for hours and reproducible from day to day.Item Open Access Fate of products of degradation processes: consequences for climatic change.(Chemosphere, 1999-03) Slanina, J; ten Brink, HM; Khlystov, AThe 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.Item Open Access The continuous analysis of nitrate and ammonium in aerosols by the steam jet aerosol collector (SJAC): extension and validation of the methodology(ATMOSPHERIC ENVIRONMENT, 2001) Slanina, J; ten Brink, HM; Otjes, RP; Even, A; Jongejan, P; Khlystov, A; Waijers-Ijpelaan, A; Hu, M; Lu, YClassical 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.