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| 2. |
- Flynn, Michael J., et al.
(författare)
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Modelling cloud processing of aerosol during the ACE-2 HILLCLOUD experiment
- 2000
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 779-800
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Tidskriftsartikel (refereegranskat)abstract
- A numerical model has been used to simulate the conditions observed during the ACE-2 Hillcloud experiment and to study the processes which may be taking place. The model incorporates gas phase chemistry of sulphur and nitrogen compounds upstream of the cloud, and the interaction of aerosol, precursor trace gases and oxidants within the cloud. Gas phase and aerosol inputs to the model have been provided from measurements made in the field. Dynamics of the air flow over the hill consisted of simple prescribed dynamics based on wind speed measurements, and also for some cases modelled dynamics. In this modelling study, it was found that during clean case studies particles down to 40-55 nm diameter were activated to form cloud droplets, the total number of droplets formed ranging from 200 to 400 drops/cm3. Significant modification of the aerosol spectra due to cloud processing was observed. In polluted cases particles down to 65-80 nm diameter were activated to form cloud droplets, the total number of droplets ranging from 800 to 2800 drops/cm3. Modification of the aerosol spectra due to cloud processing was slight. In all cases, changes in the aerosol spectra were due to both the uptake of HNO3, HCl, NH3 and SO2 from the gas phase, (the SO2 being oxidised to sulphate) and the repartitioning of species such as HNO3, HCl, and NH3 from larger particles onto smaller ones. Modelling results have been compared with observations made. Modelled droplet numbers are typically within 20% of the best measured values. The mode of the droplet distribution typically around 10-20 μm for clean cases and 4-8 μm for polluted cases was found to be in good agreement with the measured values of 10-25 μm for clean cases, but not in such good agreement for polluted cases. Measurements of upwind and interstitial aerosol distributions showed that the smallest particles activated were 30 and 50 nm for clean and polluted cases respectively, slightly smaller than the model values quoted above. Measured upwind and downwind aerosol spectra showed similar modification to that predicted by the model in eight out of the eleven model runs carried out. Chemistry measurements also give general evidence for both the uptake of species from the gas phase, and repartitioning of species from large particles onto smaller ones, though comparisons for individual cases are more difficult. From this modelling study, it can be concluded that in general, in the remote environment the exchange of hydrochloric acid, nitric acid and ammonia between aerosol particles and take up from the gas phase in the vicinity of cloud may be a very important mechanism in regulating the evolution of the aerosol spectrum. Further, the much more linear relationship between cloud droplet and accumulation mode aerosol number, which was observed in the measurements made during the ACE-2 HILLCLOUD project is supported by these modelling results. The implications of this for the indirect effect will be explored in future work.
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| 4. |
- Ferm, Martin, et al.
(författare)
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Jämförelse mellan de två vanligaste metoderna att mäta PM10 i Sverige
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- De två vanligaste metoderna för att mäta PM10-halter i Sverige, nämligen IVLs filtermetod samt TEOM-instrument (av standard typ) har jämförts i Stockholm samt en bakgrundsstation söder om Stockholm (Aspvreten). Liknande jämförelser har även gjorts i Norge. De bägge metoderna korrelerar väl vid enstaka mättillfällen. Om halten från TEOM-instrumentet plottas som funktion av filtermetoden så ger punkternas linjära regressionslinje en mätbar positiv skärning med y-axeln (ca 3 µg m-3) och en lutning av ca 0.8. Skärningen är orsakad av en inbyggd korrektionsekvation i instrumentet (PM10 = uppmätt värde x 1.03 +3 µg m-3). Om denna korrektion inte används och det uppmätta värdet från TEOM-instrumentet multipliceras med en faktor 1.3 så erhålls bästa överensstämmelsen mellan de bägge instrumenten i de mätningar som presenteras här
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| 5. |
- Gidhagen, Lars, 1951-
(författare)
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Emissions, dynamics and dispersion of particles in polluted air
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis is to yield information on how atmospheric fine and ultrafine particles are dispersed in populated areas. Quantitative information on emissions, transport and removal is needed to assess the health risks of inhalable particles. Most effort is dedicated to describe, on the local and urban scales, the distribution of ultrafine particles (and thereby also total number concentrations) originating from traffic emissions. A minor part addresses the dispersion of toxic particles of industrial origin, dispersed over regional scales. The importance of aerosol dynamics for the distribution of ultrafine particles is assessed by coupling a three-dimensional dispersion model to a monodisperse aerosol model. Meteorological forcing, sometimes in a complex geometry, is simulated by a CFD model on the local scale and by a weather forecast model on the larger scales. The principal result of the study is that particle number concentrations can, at least for Swedish conditions, be simulated and quantitatively assessed in urban models in a similar way as particle mass or gaseous pollutants. The variability of the emissions and the removal effects of coagulation and dry deposition are investigated. Vehicle emissions of particle number vary with a factor of two depending on ambient temperature, with higher concentrations during cold conditions. Other important factors that determine particle emissions are fleet composition, vehicle speed (especially for gasoline-fueled cars) and the dilution rate in the microenvironment where emissions take place. Coagulation affects particle number concentrations in highly polluted environments like car tunnels or street canyons under low wind speed conditions, while it is of less importance in the urban background (reduced number concentrations of a few percent, as compared to completely inert particles). Dry deposition is effective over the road surface, due to the velocities and turbulence produced by moving vehicles. Dry deposition also has significant effects on the urban background concentrations, reducing average levels with up to 20-30%. Dry deposition is also shown to be an important mechanism to remove fine particulate mass on the regional scale. Simulated particle number concentrations, based on emission factors determined for the local vehicle fleet and influenced by aerosol dynamic processes, are evaluated against measured concentrations for three different traffic microenvironments and also for the entire Stockholm area. Regional dispersion of arsenic in PM10 is assessed and model results compared to measurements in Central and Northern Chile.
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| 7. |
- Munthe, John, et al.
(författare)
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New concepts and methods for effect-based strategies on transboundary air pollution. Synthesis Report, April 2002
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report was prepared in connection with the scientific evaluation of the ASTA programme in May, 2002. It consists of a comprehensive summary of the approaches and results from the different ASTA sub programmes. ASTA is presently in its fourth and last year of the first phase. The report is not intended to give a full description of all relevant aspects of the problem of transboundary air pollution but rather discuss some crucial problems and their possible scientific solutions. After the preparation and submission of this report, ASTA has been positively evaluated and will continue into its second phase. The evaluation reports as well as a letter of intent for the second phase of the ASTA programme are available on the ASTA web page (http://asta.ivl.se). Further information of the programme is also available at the web page. For those who wish to receive more information of the programme, there is a list of contact persons at the end of the report. Many of the ASTA phase 1 activities are currently in a state of intense evaluation and reporting and additional scientific results as well as synthesises and assessments will be prepared during the remainder of 2002.
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| 8. |
- Tunved, Peter, et al.
(författare)
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An investigation of processes controlling the evolution of the boundary layer aerosol size distribution properties at the Swedish background station Aspvreten
- 2004
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Ingår i: Atmospheric Chemistry and Physics Discussions. - : the Copernicus GmbH (Copernicus Publications). - 1680-7367. ; 4:4, s. 4507-4543
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol size distributions have been measured at the Swedish background station Aspvreten (58.8° N, 17.4° E). Different states of the aerosol were determined using a novel application of cluster analysis. The analysis resulted in eight different clusters capturing the different stages of the aerosol lifecycle. The aerosol was interpreted as belonging to fresh, intermediate and aged type of size distribution and different magnitudes thereof. With aid of back trajectory analysis we present statistics concerning the relation of source area and different meteorological parameters using a non-lagrangian approach. Source area is argued to be important although not sufficient to describe the observed aerosol properties. Especially processing by clouds and precipitation is shown to be crucial for the evolution of the aerosol size distribution. As much as 60% of the observed size distributions present features likely related to cloud processes or wet deposition. The lifetime properties of different sized aerosols are discussed by means of measured variability. Processing by non-precipitating clouds most obviously affect aerosols in the size range 100 nm and larger. This indicates an approximate limit for activation in clouds to 100 nm in this type of environment. The aerosol lifecycle is discussed. Size distributions bearing signs of recent new particle formation (~30% of the observed size distributions) represent the first stage in the lifecycle. Aging may proceed in two directions: either growth by condensation and coagulation or processing by non-precipitating clouds. In both cases mass is accumulated. Wet removal is the main process capable of removing aerosol mass. Wet deposition is argued to be an important mechanism in reaching a state where nucleation may occur (i.e. sufficiently low aerosol surface area) in environments similar to the one studied
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| 9. |
- Tunved, Peter, 1974-
(författare)
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On the lifecycle of aerosol particles : Sources and dispersion over Scandinavia
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosol particles are likely important contributors to our future climate. Further, during recent years, effects on human health arising from emissions of particulate material have gained increasing attention. In order to quantify the effect of aerosols on both climate and human health we need to better quantify the interplay between sources and sinks of aerosol particle number and mass on large spatial scales. So far long-term, regional observations of aerosol properties have been scarce, but argued necessary in order to bring the knowledge of regional and global distribution of aerosols further. In this context, regional studies of aerosol properties and aerosol dynamics are truly important areas of investigation.This thesis is devoted to investigations of aerosol number size distribution observations performed through the course of one year encompassing observational data from five stations covering an area from southern parts of Sweden up to northern parts of Finland. This thesis tries to give a description of aerosol size distribution dynamics from both a quantitative and qualitative point of view. The thesis focuses on properties and changes in aerosol size distribution as a function of location, season, source area, transport pathways and links to various meteorological conditions.The investigations performed in this thesis show that although the basic behaviour of the aerosol number size distribution in terms of seasonal and diurnal characteristics is similar at all stations in the measurement network, the aerosol over the Nordic countries is characterised by a typically sharp gradient in aerosol number and mass. This gradient is argued to derive from geographical locations of the stations in relation to the dominant sources and transport pathways. It is clear that the source area significantly determine the aerosol size distribution properties, but it is obvious that transport condition in terms of frequency of precipitation and cloudiness in some cases even more strongly control the evolution of the number size distribution. Aerosol dynamic processes under clear sky transport are however likewise argued to be highly important.Southerly transport of marine air and northerly transport of air from continental sources is studied in detail under clear sky conditions by performing a pseudo-Lagrangian box model evaluation of the two type cases. Results from both modelling and observations suggest that nucleation events contribute to integral number increase during southerly transport of comparably clean marine air, while number depletion dominates the evolution of the size distribution during northerly transport. This difference is largely explained by different concentration of pre-existing aerosol surface associated with the two type cases. Mass is found to be accumulated in many of the individual transport cases studied. This mass increase was argued to be controlled by emission of organic compounds from the boreal forest. This puts the boreal forest in a central position for estimates of aerosol forcing on a regional scale.
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