Emission and dry deposition of accumulation mode particles in the Amazon Basin 1Department of Applied Environmental Science, Stockholm University, Sweden
2Institute of Physics, University of São Paulo, Brazil
Received: 02 April 2010 – Published in Atmos. Chem. Phys. Discuss.: 08 June 2010 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.
Revised: 21 October 2010 – Accepted: 25 October 2010 – Published: 03 November 2010
Size-resolved net particle fluxes of the five lowest size bins, representing
0.25–0.45 μm in diameter, were in general dominated by deposition 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. Transfer velocities within this particle size range
were observed to increase linearly with increasing friction velocity and
increasing particle diameter.
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 upward fluxes were observed. However, in wind sectors
associated with higher anthropogenic influence, deposition fluxes dominated.
The net upward fluxes were interpreted as a result of primary biogenic
aerosol emission, but deposition of anthropogenic particles seems to have
masked this emission in wind sectors with higher anthropogenic influence.
The net emission fluxes were at maximum in the afternoon when the mixed
layer is well developed, and were best correlated with horizontal wind speed
according to the equation
log10 F=0.48 · U+2.21
where F is the net emission number flux of 0.5–2.5 μm particles
[m−2 s−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 dry deposition of accumulation mode particles in the Amazon Basin, Atmos. Chem. Phys., 10, 10237-10253, doi:10.5194/acp-10-10237-2010, 2010.