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Aerosol number fluxes over the Amazon rain forest during the wet season
Stockholm University, Faculty of Science. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
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2009 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, no 24, 9381-9400 p.Article in journal (Refereed) Published
Abstract [en]

Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.

Place, publisher, year, edition, pages
2009. Vol. 9, no 24, 9381-9400 p.
National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-38537ISI: 000273060200004OAI: oai:DiVA.org:su-38537DiVA: diva2:310932
Available from: 2010-04-19 Created: 2010-04-19 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Aerosol Exchange between Forests and the Atmosphere: Fluxes over a Tropical and a Boreal Forest
Open this publication in new window or tab >>Aerosol Exchange between Forests and the Atmosphere: Fluxes over a Tropical and a Boreal Forest
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main goal of this thesis was to investigate primary biogenic aerosol emission from the Amazon rain forest through measurements of vertical turbulent aerosol number fluxes. In addition, the particle dry deposition sink has been analysed and quantified, and is also compared with the dry deposition sink at a boreal forest site.

The total aerosol number flux of particles with diameter larger than 10 nm was dominated by downward fluxes at the rain forest site, even in the most pristine conditions in the wet season. This is an indication that the primary biogenic aerosol number source is small when considering the total particle size spectrum. However, size resolved aerosol number fluxes indicated net emission for particles with dry diameter 0.5-2.5 μm in clean conditions. These emission fluxes are likely explained by a primary biogenic aerosol source from the rain forest and seemed to be best correlated with horizontal wind speed, peaking during afternoon. Even though there are few particles in this diameter interval, typically one particle per cm3, they could potentially play an important role as giant nuclei in warm rain initiation.

Average particle number based dry deposition velocities over the whole aerosol population were lower at the rain forest site than at the boreal forest site. The reasons are likely the high fraction of accumulation mode particles at the rain forest site and low wind speeds in the tropics compared to the midlatitudes.

This thesis provides a relation describing emission of particles with diameter 0.5-2.5 μm from the rain forest, as a function of wind speed. In addition, linear equations relating average dry deposition velocity of the total aerosol number population to friction velocity are suggested for both the wet and dry season at the rain forest site. Finally, this thesis provides a relationship between dry deposition velocity of particles within the diameter range 0.25-0.45 μm, friction velocity and particle diameter.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University, 2010. 42 p.
National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-38544 (URN)978-91-7447-051-2 (ISBN)
Public defence
2010-05-28, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.Available from: 2010-05-06 Created: 2010-04-19 Last updated: 2011-05-25Bibliographically approved

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