| 1. |
- Andersson, Camilla, 1979-
(författare)
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Air Pollution Dependency on Climate Variability and Source Region : Past, Current and Future Air Pollution Scenarios over Europe
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objectives of this thesis were to investigate the dependency of European air pollution on climate variability and emission source region. Calculations with a chemistry transport model (CTM) were conducted to investigate the influence of climate variability. The CTM was forced by both simulated past (a re-analysis spanning 1958-2001) and future (a climate simulation spanning 1961-2100) meteorology keeping anthropogenic emissions constant. To investigate the influence of emission source region emissions were varied in western, eastern and northern Europe in seven-year (1997-2003) simulations. The main conclusions in this thesis are § There is variability in air pollution due to climate variability on time scales from year to year to decades and long-term trends. Hence, what is measured now will not be valid in a decade, or even next year. § Interannual variability in air pollution due to climate variability is greater than interannual variability in anthropogenic emissions. § The extreme conditions in 2003, resulting in elevated surface O3 concentrations, could be an indication on what we can expect in the future. § The trend in surface O3 over the past due to climate change is similar to the projected trend due to future climate change: increasing in south-western and central Europe and decreasing in north-eastern Europe. § Changes in isoprene emissions and dry deposition dependency on soil moisture are of importance for changes in surface O3 in central and southern Europe. It is vital to include these processes, especially the latter in climate change effect studies of surface O3. § This work indicates that it is of greater importance for health benefits of the European population to reduce primary PM emissions than precursors of secondary inorganic aerosol under the assumption of higher relative risk for primary PM. This is especially the case in western Europe.
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| 2. |
- Acosta Navarro, Juan Camilo, 1983-
(författare)
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Anthropogenic influence on climate through changes in aerosol emissions from air pollution and land use change
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Particulate matter suspended in air (i.e. aerosol particles) exerts a substantial influence on the climate of our planet and is responsible for causing severe public health problems in many regions across the globe. Human activities have altered the natural and anthropogenic emissions of aerosol particles through direct emissions or indirectly by modifying natural sources. The climate effects of the latter have been largely overlooked. Humans have dramatically altered the land surface of the planet causing changes in natural aerosol emissions from vegetated areas. Regulation on anthropogenic and natural aerosol emissions have the potential to affect the climate on regional to global scales. Furthermore, the regional climate effects of aerosol particles could potentially be very different than the ones caused by other climate forcers (e.g. well mixed greenhouse gases). The main objective of this work was to investigate the climatic effects of land use and air pollution via aerosol changes.Using numerical model simulations it was found that land use changes in the past millennium have likely caused a positive radiative forcing via aerosol climate interactions. The forcing is an order of magnitude smaller and has an opposite sign than the radiative forcing caused by direct aerosol emissions changes from other human activities. The results also indicate that future reductions of fossil fuel aerosols via air quality regulations may lead to an additional warming of the planet by mid-21st century and could also cause an important Arctic amplification of the warming. In addition, the mean position of the intertropical convergence zone and the Asian monsoon appear to be sensitive to aerosol emission reductions from air quality regulations. For these reasons, climate mitigation policies should take into consideration aerosol air pollution, which has not received sufficient attention in the past.
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| 3. |
- Ekström, Sanna, 1980-
(författare)
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The influence of biogenic organic compounds on cloud formation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosols and clouds provide the largest uncertainty in the atmospheric radiation budget. The main focus of this thesis was to investigate the ability of organic compounds in aerosol particles to form clouds, and more specifically those emitted by living organisms. The cloud forming properties of the highly water-soluble methyltetrols and polyols, which are compounds produced by plants and fungi that are common in aerosol, were studied. All compounds and their salt mixtures have a moderate potential to serve as cloud condensation nuclei (CCN). They are thus not likely to have a significant global impact on cloudiness. The potential presence of surfactants released by microorganisms was investigated for aerosols sampled at different locations. Very low surface tension values were measured for these aerosol extracts (30 mN/m), which implies that these aerosols have good CCN properties and indicate the presence of biosurfactants. Their occurrence in aerosols still needs to be confirmed directly by chemical identification. Reactions of organic compounds in sulfate salt solutions exposed to UV-light were studied and found to produce surface active compounds. Thus, mixed sulfate/organic aerosol could have more favourable CCN properties after exposure to light than when kept in the dark. The surface active compounds were proposed to be long-chained organosulfates with hydrophilic and hydrophobic parts, similar to other amphiphilic surfactants. Mixtures of salt and strong surfactants formed by bacteria were studied using two different techniques for determining their CCN properties. There were inconsistencies between the two methods which could be accounted for by surface partitioning. The studied mixtures were determined to be good potential CCN material in both techniques. All these aspects require further investigation, but if the impact of strong biogenic surfactants on cloud formation is confirmed, a new link between living organisms and climate would be identified.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Wallén, Anna, 1962-
(författare)
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Measuring Elemental Carbon in Occupational Environments
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbonaceous aerosol particles from combustion, such as diesel exhaust particles (DEP), harm human health and affect the Earth’s radiative system.Elemental carbon (EC) has been proposed to be used as a marker of DEP. The objective of this thesis was to investigate the EC levels in different environments, to compare methods for measuring EC and investigate confounding factors that influence EC. The five papers concluded the following: A study of asphalt paving work showed levels of respirable EC at 3 µg m-3 and organic carbon (OC) level at 42 µg m-3. The concentration of OC was not high enough to disturb the light absorption of EC in the analysis. The EC/TC ratio 0.067 indicated a large contribution of OC from the asphalt fumes. Water-soluble organic compounds (WSOC) were used to show that samples with wood smoke particles, both single source and ambient, resulted in a positive bias of 10-20 % in EC due to WSOC, but not for samples with DEP. Well-defined single source samples of DEP gave differing EC and even total carbon levels in an intercomparison between three different analysing methods. Bio fuels such as vegetable oils, animal fat and natural gas showed very large difference in the amount of EC. A study of aerosol in the subway shows that iron oxides interfere with the analysis of EC. Analytical result and the oxidation state of iron in samples after analysis differed between NIOSH and IMPROVE. Optical measurements of Black Carbon (BC) in the subway were higher than at street level, which was suspected to be an overestimation of BC due to iron oxides. The apparent attenuation cross section, σATN (m2/g) was compared for different samples, different protocols and varying load during thermo-optical analysis to validate the setting of the OC/EC split point. The results indicating a mixed combustion of pyrolytic carbon with EC and the assumptions forming the basis for setting a proper split time between EC and OC do not seem to be valid.
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