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Dry deposition of NaCl aerosols: theory and method for a modified leaf-washing technique
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Naturresurshushållning)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Naturresurshushållning)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
Lund University. (Department of Physics)
2010 (English)In: Atmospheric Measurement Techniques Discussions, ISSN 1867-8610, E-ISSN 1867-8610, Vol. 3, no 4, 3851-3876 p.Article in journal (Refereed) Published
Abstract [en]

Within the framework of aerosol deposition to vegetation we present a specially designed leaf wash-off method used in a wind-tunnel based study, where leaves of Quercus robur L. were exposed to NaCl aerosols. We summarise the principles and illustrate the method for two types of substances, the chloride ion and the sodium ion, and for two levels of aerosol exposure prior to leaf washing. On the average, in the low-exposure experiments (S1), the 1st (2nd) wash-off step provided 90% (96%) of the amount of Cl− on the leaves. In the high-exposure experiments (S2) the corresponding values were 96% and 99%. For sodium, the general dynamics resembles that of chloride, but the amounts washed off were, in both series, on the average below what would be expected if the equivalent ratio in the tunnel aerosol were to be preserved. Na+ showed adsorption and/or absorption at the leaf surfaces. The difference between the mean values of the amounts of chloride and of sodium washed off in S1 was not statistically significant, the mean Na+ to Cl− difference as a fraction of Cl− being minus 18%±27%; corresponding values for S2 were minus 16%±9%, however (p<0.05). In the latter case, 101±57 μequiv Na+ per m2 of leaf area were missing for the equivalent relationship 1:1 with Cl− to be met. Although uncertainties are thus large, this indicates the magnitude of the Na+-retention. The method is suitable not only for chloride, an inexpensive and easy-to-handle tracer, but also for sodium under exposure at high aerosol concentrations. Our findings will help design further studies of aerosol/forest interactions.

Place, publisher, year, edition, pages
Copernicus Publications on behalf of the European Geosciences Union , 2010. Vol. 3, no 4, 3851-3876 p.
Keyword [en]
aerosol deposition, sodium ion, chloride ion, Quercus robur leaves
National Category
Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
URN: urn:nbn:se:lnu:diva-11854DOI: 10.5194/amtd-3-3851-2010OAI: oai:DiVA.org:lnu-11854DiVA: diva2:418530
Available from: 2011-05-23 Created: 2011-05-23 Last updated: 2016-07-08Bibliographically 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. 190 p.
Series
Linnaeus University Dissertations, 43/2011
Keyword
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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