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On the lifecycle of aerosol particles: Sources and dispersion over Scandinavia
Stockholm University, Faculty of Science, Department of Meteorology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU) , 2004. , 176 p.
Keyword [en]
aerosols
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-223ISBN: 91-628-6214-6 (print)OAI: oai:DiVA.org:su-223DiVA: diva2:191143
Public defence
2004-09-22, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00
Opponent
Supervisors
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
List of papers
1. One year boundary layer aerosol size distribution data from five Nordic background stations
Open this publication in new window or tab >>One year boundary layer aerosol size distribution data from five Nordic background stations
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2003 (English)In: Atmospheric Chemistry and Physics, ISSN 1680-7316, Vol. 3, 2183-2205 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23276 (URN)
Note
Part of urn:nbn:se:su:diva-223Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-29Bibliographically approved
2. Aerosol characteristics of air masses in Northern Europe – influences of location, transport, sinks and sources
Open this publication in new window or tab >>Aerosol characteristics of air masses in Northern Europe – influences of location, transport, sinks and sources
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2005 (English)In: Journal of Geophysical Research, ISSN 0148-0227, ISSN 0148-0227, Vol. 110, no D7, D07201- p.Article in journal (Refereed) Published
Abstract [en]

Synoptic-scale air masses at different stations were classified following a definition based on Berliner Wetterkarte. This air mass classification has been related to 1 year of aerosol number size distributions measurements performed at four different stations extending from Aspvreten in Sweden (58.8 degrees N) to Pallas in northern Finland (68 degrees N). The air mass classification describes both class of air mass, based on the origin of the air mass, and character of air in terms of marine, mixed, and continental air masses. The aerosol size distribution properties were evaluated in relation to the air masses. Emphasis was put on the differences between marine, mixed, and continental character air masses. It is shown that continental air masses exceed marine and mixed character air masses both in number and mass concentration. Different classes of air masses were further associated with different aerosol size distribution properties. It is also shown that although serving as a somewhat good qualifier for the aerosol at individual stations, the air mass classification cannot be used to estimate the aerosol burden over large geographical areas. Instead, a sharp gradient was shown to exist between different stations, although aerosol properties were observed in equal air masses according to the definition by Berliner Wetterkarte. This gradient manifests as a south-northerly decrease in aerosol total number and volume, indicating that the aerosol properties including the aerosol size distribution are less conservative than the thermodynamic properties (e.g., pseudo-potential temperature and humidity profiles) that characterize the different air masses. Further, using a pseudo-Lagrangian approach, the aerosol turnover time was estimated for different sized aerosols in air moving from south to north (i.e., depletion of aerosols in air arriving from the continent). Turnover time of Aitken particles was found to be in the range of 1-2 days, while accumulation mode turnover time was estimated to be in the order of 2-3 days

Place, publisher, year, edition, pages
American Physical Union, 2005
Keyword
size distribution, boreal forest
Identifiers
urn:nbn:se:su:diva-23277 (URN)10.1029/2004JD005085 (DOI)
Note
Part of urn:nbn:se:su:diva-223Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-08Bibliographically approved
3. An investigation of processes controlling the evolution of the boundary layer aerosol size distribution properties at the Swedish background station Aspvreten
Open this publication in new window or tab >>An investigation of processes controlling the evolution of the boundary layer aerosol size distribution properties at the Swedish background station Aspvreten
2004 (English)In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, Vol. 4, no 4, 4507-4543 p.Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
the Copernicus GmbH (Copernicus Publications), 2004
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-23278 (URN)
Note
Part of urn:nbn:se:su:diva-223Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-08Bibliographically approved
4. A pseudo-Lagrangian model study of the size distribution properties over Scandinavia: Transport from Aspvreten to Värriö
Open this publication in new window or tab >>A pseudo-Lagrangian model study of the size distribution properties over Scandinavia: Transport from Aspvreten to Värriö
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2004 (English)In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, no 4, 7757-7794 p.Article in journal (Refereed) Published
Abstract [en]

The evolution of the aerosol size distribution during transport between Aspvreten (58.8° N, 17.4° E) and Värriö (67.46° N, 29.35° E) was studied using a pseudo-Lagrangian approach. Aerosol dynamic processes were studied and interpreted utilizing a state-of-the-art aerosol dynamic box model UHMA (University of Helsinki Multicomponent Aerosol model) complemented with OH, NO3, O3 and terpene chemistry. In the model simulations, the growth and formation of aerosol particles was controlled by sulphuric acid, ammonia, water and an unidentified low volatile organic compound. This organic compound was assumed to be a product of terpene oxidation with a yield of 13% in the base case conditions. Changes of aerosol size distribution properties during transport between the stations were examined in twelve clear sky cases. On average, the modelled number agreed fairly well with observations. Mass concentration was overestimated by 10%. Apart from dilution, the only removal mechanism for aerosol mass is dry deposition. A series of sensitivity tests performed revealed that the absolute magnitude of dry deposition effects on the aerosol size distribution is slow overall. Furthermore, nucleation does not leave a significant contribution to aerosol number in the selected cases. The sensitivity of the modelled size distribution to concentration of precursor gases and oxidants is, however, obvious. In order to explain observed mass increase during transport we conclude that a yield of low volatile products from oxidation of terpenes of 10–15% is required to explain observed growth rates. Coagulation is acknowledged to be highly important in modelled cases.

National Category
Environmental Sciences Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-23279 (URN)10.5194/acpd-4-7757-2004 (DOI)
Note
Part of urn:nbn:se:su:diva-223Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-11-02Bibliographically approved
5. Is nucleation capable of explaining observed aerosol integral number increase during southerly transport over Scandinavia?
Open this publication in new window or tab >>Is nucleation capable of explaining observed aerosol integral number increase during southerly transport over Scandinavia?
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Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23280 (URN)
Note
Part of urn:nbn:se:su:diva-223Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-13Bibliographically approved

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