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Aerosol Deposition at the Sea/Land Interface: Pilot Experiments Using a Wind Tunnel
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Naturresurshushållning)
2004 (English)In: The ESS Bulletin, ISSN 1651-5382, Vol. 2, no 1, p. 47-73Article in journal (Refereed) Published
Abstract [en]

Climate change in terms of meteorological shift or change affects the atmospheric aerosol behavior that in turn affects the ecosystems by changing their biogeochemistry in rather unpredictable ways. These linkages therefore pose risks to natural resources and thus to society.

 There are strong needs to advance the understanding of coastal-forest ecosystems, in particular with respect to sea-forest linkages and atmosphere/canopy exchange.

 This paper addresses a wind-water tunnel approach as one of the ways to study meteorological and biogeochemical effects of atmospheric aerosols. The aim of the paper is to advance the understanding of atmospheric aerosol physical properties (e.g. particle size distributions) in an experimental situation and to study basic characteristics of the wind tunnel such as aerodynamics and wind patterns.

During the experimental runs it was observed that at the start-up stage particle concentration tends to decline. After start of the aerosol generator the concentration curves begin to increase and grow towards equilibrium. In concentration equilibrium (steady state), the aerosol source strength balances the aerosol sink strength. It was observed that the fine particles (0.3-0.5 μm) and the coarse particles (3-5 μm and larger than 5 μm) behave differently in some respects. In particular, coarse particles show more noise in the concentration variations. This is because coarse particles deposited onto tunnel walls or propeller blades might occasionally become re-suspended into the tunnel air, resulting in momentarily high values in the coarse particle Laser Particle Counter (LPC) counting channel. Since the particle size determines a wide range of physical and chemical characteristics and behavior, including the distances across which particles can be transported, and also deposition rates of substances carried by particles of given sizes, information about particle size distributions is fundamental. The experiments provide valuable information about the performance of the wind tunnel and some essential aerosol properties within the wind tunnel.

Place, publisher, year, edition, pages
Kalmar: ESS, Kalmar University , 2004. Vol. 2, no 1, p. 47-73
Keywords [en]
aerosols, dry deposition, coastal zone forest ecosystem, edge effect, wind tunnel
National Category
Natural Sciences
Research subject
Natural Science, Environmental Science
Identifiers
URN: urn:nbn:se:lnu:diva-11852OAI: oai:DiVA.org:lnu-11852DiVA, id: diva2:418505
Available from: 2011-05-23 Created: 2011-05-23 Last updated: 2011-06-09Bibliographically approved
In thesis
1. Aerosol deposition to coastal forests: a wind tunnel approach
Open this publication in new window or tab >>Aerosol deposition to coastal forests: a wind tunnel approach
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aerodynamically rough surfaces of forests provide for efficient air/ canopy exchange of mass, heat and momentum. In that context, the effects of forest edges come into focus, and therefore, coastal-zone forests constitute aparticular concern. Aerosol-sink modelling is of importance to the global-scalecontext, because sink strengths influence the concentration of aerosol particles in the atmosphere, and that concentration, in turn, influences climate. Dry deposition models are insufficient due to a lack of semi-empirical data and because of difficulties in parameterization of the efficiency (E) with which leaves capture aerosols. Quantifications of such parameters promote possibilities for modelling aerosol-sink processes within various canopy layers. This thesis focuses on studies of sea-salt aerosol dry deposition within models of oak canopies exposed to artificially generated aerosols in a wind tunnel. The overall goal is to advance the understanding of deposition processes in forest ecosystems. Aims are to determine capture efficiencies and deposition velocities (Vd) for oak (Quercus robur L.), to investigate E and Vd dependence on aerosol particle size, wind velocity and vegetation structural elements such as Leaf Area Index (LAI), to explore edge effects on deposition, to relate my results to natural situations in the field, and to address modelling applications. This thesis is a result of five studies. The first study is based on developing awind tunnel approach with a main focus on establishing reference conditions.The next step is to quantify E and provide estimates of how E, with respect toa well defined mass-vs-particle-size distribution, varies with wind speed. To that end, a special wash-off technique is developed. Finally, edge effects ondeposition processes are investigated. Results demonstrate that forest ecosystems would experience substantially increased deposition at edges. The findings suggest that field measurements of deposition in the interior of a forest “island” in an otherwise open landscape would underestimate the deposition to the entire forest. Results clearly indicate needs for further research on the effects of LAI on capture efficiency and deposition velocity. The obtained capture efficiencies can be translated into deposition velocities for trees with a specific leaf area. An increase of Vd with increasing wind speed is found, and is consistent with other studies. Results confirm advantages of the wind tunnel approach, including its ability to enable experiments under controlled conditions. However, several problems require that explicit sub-models be developed of wind-speed dependent effects on leaf posture in the aerosol flow field and that gradients in relative humidity close to leaf surfaces need further attention. The results also propose needs for a range of further experimental investigations regarding aerosol deposition across the complete sea-to-land aerodynamic transition.

Place, publisher, year, edition, pages
Växjö, Kalmar: Linnaeus University Press, 2011. p. 190
Series
Linnaeus University Dissertations ; 43/2011
Keywords
NaCl aerosol, dry deposition, climate change, coastal-zone forest, Quercus robur, wind tunnel, edge effect
National Category
Natural Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-11999 (URN)978-91-86491-71-0 (ISBN)
Public defence
2011-05-06, A137, Landgången 4, Kalmar, 09:30 (English)
Opponent
Supervisors
Available from: 2011-06-07 Created: 2011-05-30 Last updated: 2011-06-07Bibliographically approved

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