| 1. |
- Bower, K. N., et al.
(författare)
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The Great Dun Fell experiment 1995 : An overview
- 1999
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Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 151-184
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Tidskriftsartikel (refereegranskat)abstract
- During March and April of 1995 a major international field project was conducted at the UMIST field station site on Great Dun Fell in Cumbria, Northern England. The hill cap cloud which frequently envelopes this site was used as a natural flow through reactor to examine the sensitivity of the cloud microphysics to the aerosol entering the cloud and also to investigate the effects of the cloud in changing the aerosol size distribution, chemical composition and associated optical properties. To investigate these processes, detailed measurements of the cloud water chemistry (including the chemistry of sulphur compounds, organic and inorganic oxidised nitrogen and ammonia), cloud microphysics and properties of the aerosol and trace gas concentrations upwind and downwind of the cap cloud were undertaken. It was found that the cloud droplet number was generally strongly correlated to aerosol number concentration, with up to 2000 activated droplets cm-3 being observed in the most polluted conditions. In such conditions it was inferred that hygroscopic organic compounds were important in the activation process. Often, the size distribution of the aerosol was substantially modified by the cloud processing, largely due to the aqueous phase oxidation of S(IV) to sulphate by hydrogen peroxide, but also through the uptake and fixing of gas phase nitric acid as nitrate, increasing the calculated optical scattering of the aerosol substantially (by up to 24%). New particle formation was also observed in the ultrafine aerosol mode (at about 5 nm) downwind of the cap cloud, particularly in conditions of low total aerosol surface area and in the presence of ammonia and HCl gases. This was seen to occur at night as well as during the day via a mechanism which is not yet understood. The implications of these results for parameterising aerosol growth in Global Climate Models are explored.
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| 2. |
- Choularton, T. W., et al.
(författare)
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The Great Dun Fell Cloud Experiment 1993 : An overview
- 1997
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Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2393-2405
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Tidskriftsartikel (refereegranskat)abstract
- The 1993 Ground-based Cloud Experiment on Great Dun Fell used a wide range of measurements of trace gases, aerosol particles and cloud droplets at five sites to study their sources and sinks especially those in cloud. These measurements have been interpreted using a variety of models. The conclusions add to our knowledge of air pollution, acidification of the atmosphere and the ground, eutrophication and climate change. The experiment is designed to use the hill cap cloud as a flow-through reactor, and was conducted in varying levels of pollution typical of much of the rural temperate continental northern hemisphere in spring-time.
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| 3. |
- Berg, Olle H., et al.
(författare)
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Comparison of observed and modeled hygroscopic behavior of atmospheric particles
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 47-64
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Forskningsöversikt (refereegranskat)abstract
- The hygroscopic behavior of sub-micrometer atmospheric aerosol particles was studied with a Tandem Differential Mobility Analyzer (TDMA) at a field site in the Po Valley, Italy. The measurements were done in a continental polluted aerosol during the CHEMDROP fog and haze field experiment at San Pietro di Capofiume in November 1994. In this study, hygroscopic diameter growth factors of individual particles were measured when taken from a dry state, to a relative humidity of 90 %. The aerosol consisted of two groups of particles with different hygroscopic properties, as also seen in an earlier field experiment at the same location in 1989 and at other continental sites. The present work is a closure study on the hygroscopic behavior of sub-micrometer aerosol particles and their mass. Ammonium sulfate was used to model the hygroscopic growth with a model based on thermodynamic data for non-ideal aqueous solutions at water vapor subsaturation. The study was made in two steps: The first step is a comparison between hygroscopic active aerosol volume fractions derived from TDMA measurements on individual particles integrated over the particle size distributions, and collected volume fractions of major ions sampled by size resolved cascade impactors. The model of hygroscopic growth was also used, in the second step, to calculate ambient sizes of individual aerosol particles. These sizes were then compared to the actual ambient sizes as measured by the Droplet Aerosol Analyzer. The result shows agreement, within the estimated errors, between the integrated hygroscopic active volume fractions and the collected volume fractions of inorganic salts, for five events out of six studied. A mass balance could also be obtained between the masses collected with the impactors and the integrated volume distributions, by attributing reasonable densities to the hygroscopically active and inactive fractions. The differences between the calculated and measured ambient sizes were within measurement errors, when Raoult's law was used to model the occasions with relative humidities larger than 95 %.
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| 4. |
- Cederfelt, S. I., et al.
(författare)
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Field validation of the droplet aerosol analyser
- 1997
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Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2657-2670
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Tidskriftsartikel (refereegranskat)abstract
- A new instrument for the study of cloud droplets and its relation to aerosol particles, the droplet aerosol analyser (DAA), was for the first time used in a field campaign. The DAA has the unique feature of measuring the ambient size of cloud droplets or cloud interstitial aerosol particles together with the size of its dry residue. This is obtained with a two-parameter data acquisition technique which results in a three-dimensional data set (ambient size, dry residue size, number concentration). The principle and design of the DAA is briefly described. The DAA was intercompared with differential mobility particle sizers, particulate volume monitors and a forward scattering spectrometer probe with respect to interstitial and cloud droplet dry residue size distribution as well as particle-size-dependent scavenging due to cloud droplet nucleation and for cloud droplet number concentration and size distribution and cloud liquid water concentration. Overall, the DAA showed good agreement with respect to all these six aerosol/cloud properties.
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| 5. |
- Frank, M, et al.
(författare)
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Particle size dependent CO dissociation on alumina-supported Rh: a model study
- 1997
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Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 279:1-2, s. 92-99
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Via deposition of Ph from the gas phase onto a thin, well-ordered alumina film we have prepared various of alumina-supported Rh particle systems. The morphologies and particle sizes have been characterised with spot profile analysis LEED and STM measureme
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| 6. |
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| 7. |
- Fuzzi, Sandro, et al.
(författare)
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Overview of the Po valley fog experiment 1994 (CHEMDROP)
- 1998
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Ingår i: Contributions to Atmospheric Physics. - 0005-8173. ; 71:1, s. 3-19
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Forskningsöversikt (refereegranskat)abstract
- The paper presents an outline of the CHEMDROP field experiment, carried out in November 1994 at the field station of S. Pietro Capofiume in the Po Valley, Italy. The main objective of the project was to address the issue of the size-dependent chemical composition of fog droplets, by experimentally investigating the following processes, which are expected to affect (or be affected by) the chemical composition of fog droplets as a function of size: a) the connection of the size-dependent chemical composition of CCN to the size-dependent composition of fog droplets; b) the gas/liquid partitioning of the gaseous species NH3, SO2, HCHO, HNO3 in fog; c) the Fe(II)/Fe(III) redox cycle in fog water. Some general results and overall conclusions of the experiment are reported in this paper, while more specific scientific questions are discussed in other companion papers in this issue. CHEMDROP results show that several processes concur in determining the size-dependence of fog droplets chemical composition: nucleation scavenging of pre-existing CCN, fog dynamical evolution and gas/liquid exchange between interstitial air and fog droplets. Chemical transformations in the liquid phase can cause further changes in the chemical composition of the droplets. Only by taking into account the combination of all these processes, is it possible to explain the inhomogeneities in fog droplet chemical composition.
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| 8. |
- Andersson, S, et al.
(författare)
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CO dissociation characteristics on size-distributed rhodium islands on alumina model substrates
- 1998
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Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 108:7, s. 2967-2974
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The dissociation of CO on size-distributed Rh particles supported on a thin alumina film has been studied with high resolution X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). Adsorbed CO dissociates upon heating to temperat
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| 9. |
- Andersson, S, et al.
(författare)
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Metal-oxide interaction for metal clusters on a metal-supported thin alumina film
- 1999
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Ingår i: SURFACE SCIENCE. - : ELSEVIER SCIENCE BV. ; 442:1
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The interaction between deposited metal clusters and a thin model alumina film grown on NiAl(110) have been studied using X-ray absorption spectroscopy (XAS) and core and valence photoelectron spectroscopy. A lower limit for the fundamental gap of the sup
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| 10. |
- Andersson, S, et al.
(författare)
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Temperature dependent XPS study of CO dissociation on small Rh particles
- 1998
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Ingår i: VACUUM. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X. ; 49:3, s. 167-170
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have used temperature dependent X-ray Photoelectron Spectroscopy (XPS) to study the heating-induced CO dissociation on oxide-supported Rh particles through observation of changes undergone by the adsorbate CO and the formation of atomic carbon from the
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