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| Titel |
Aerosol fluxes and dynamics within and above a tropical rainforest in South-East Asia |
| VerfasserIn |
J. D. Whitehead, M. W. Gallagher, J. R. Dorsey, N. Robinson, A. M. Gabey, H. Coe, G. McFiggans, M. J. Flynn, J. Ryder, E. Nemitz, F. Davies |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 19 ; Nr. 10, no. 19 (2010-10-05), S.9369-9382 |
| Datensatznummer |
250008806
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| Publikation (Nr.) |
 copernicus.org/acp-10-9369-2010.pdf |
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| Zusammenfassung |
| Atmospheric aerosol measurements were conducted near Danum Valley, in the
Malaysian state of Sabah, North-East Borneo, as part of the OP3 and ACES
projects, in April and June/July 2008. Here, aerosol fluxes and diurnal
variability in and above the rainforest canopy were examined in order to gain
an understanding of their behaviour in the surface layer of the South-East
Asian rainforest. Aerosol fluxes were calculated by eddy covariance from
measurements above the rainforest canopy on the Global Atmosphere Watch (GAW)
tower. Upward fluxes were seen on most mornings between 09:00 and 11:00 local
time and this could be attributed to venting of the nocturnal boundary layer
as it broke up in the morning. Measurements were also conducted
within the canopy and trunk space at a nearby site. Profiles in aerosol number concentrations
were investigated using GRIMM Optical Particle Counters (OPCs) at various
levels within the rainforest canopy and trunk space, as well as a single OPC on a vertically
moving platform. These showed an overnight increase in larger particles (1–20 μm) at all levels, but much more prominently near the top of
the canopy, which could be attributed to fog formation. At ground level,
number concentrations in this size range correlated with enhancements in
biological aerosol concentrations, measured using a Wide Issue Bioaerosol
Spectrometer (WIBS) located near the forest floor, suggesting that coarse
particle number concentrations were dominated by biological aerosols. A
comparison of particle number concentrations (in the size range
0.5–1.0 μm) between above canopy and the trunk space showed correlations,
despite turbulence data suggesting persistent decoupling between the two
measurement sites. These correlations often relied on a shift of the particle
time-series against each other, implying a time delay in observations between
the sites, which varied according to time of day. This lag time was shortest
during the middle of the day by a significant margin. This was not observed
for aerosols larger than 1.0 μm. Further evidence of daytime
coupling between above canopy and the trunk space in terms of aerosol measurements is
implied by comparison of measurements from an Aerosol Mass Spectrometer (AMS)
at the GAW tower and simultaneous bag sampling at the in-canopy site,
subsequently analysed with the AMS. Transport of particles through the canopy
seems to occur through large-scale, sporadic turbulent events, suggesting
that the coupling between the canopy space and the air above is due to these
ventilation events. |
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