Atmos. Chem. Phys. Discuss., 10, 14013-14052, 2010
www.atmos-chem-phys-discuss.net/10/14013/2010/
doi:10.5194/acpd-10-14013-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Emission and deposition of accumulation and coarse mode particles in the Amazon basin
L. Ahlm1, R. Krejci1, E. D. Nilsson1, E. M. Mårtensson1, M. Vogt1, and P. Artaxo2
1Department of Applied Environmental Science, Stockholm University, Sweden
2Institute of Physics, University of São Paulo, Brazil

Abstract. Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison.

Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, pointed downward in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net emission fluxes dominated. However, in wind sectors associated with higher anthropogenic influence, net deposition fluxes dominated. The net emission fluxes were interpreted as primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and these emissions were best correlated with horizontal wind speed by the equation

log10F=0.47·U+2.26

where F is the emission number flux of 0.5–2.5 μm particles [m−2s−1] and U is the horizontal wind speed [ms−1] at the top of the tower.


Citation: Ahlm, L., Krejci, R., Nilsson, E. D., Mårtensson, E. M., Vogt, M., and Artaxo, P.: Emission and deposition of accumulation and coarse mode particles in the Amazon basin, Atmos. Chem. Phys. Discuss., 10, 14013-14052, doi:10.5194/acpd-10-14013-2010, 2010.
 
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