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ACPD

Atmospheric Chemistry and Physics Discussions

ACPD

1680-7375

Copernicus GmbH

Göttingen, Germany

10.5194/acpd-9-18965-2009

Measurements of coarse mode and primary biological aerosol transmission through a tropical forest canopy using a dual-channel fluorescence aerosol spectrometer

Gabey

A. M.

¹ Gallagher

M. W.

¹ Whitehead

¹ Dorsey

Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, UK

11 09 2009

9 5 18965 18984

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This article is available from http://www.atmos-chem-phys-discuss.net/9/18965/2009/acpd-9-18965-2009.html

The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/18965/2009/acpd-9-18965-2009.pdf

Aerosol in the size range 0.8–20 μm was characterized according to optical equivalent diameter, DP, morphology and the presence of biological material, the latter determined by recording fluorescence excited by ultraviolet light pulses at two different wavelengths. Single-particle measurements were performed within and subsequently above a tropical rainforest in Borneo, Malaysia, in June and July 2008. In both locations the aerosol number size distribution exhibited a primary biological aerosol (PBA) mode sized 2 μm<DP<20 μm and much larger in number within the forest than above it, suggesting the PBA originates below the canopy. PBA was observed to dominate the total number at DP>2 μm and possessed a wider morphological range than non-PBA. It also accounted for around 80% of the total number in the understory and 40% of the total number above canopy. Canopy transmission efficiencies for the total aerosol number and PBA are calculated to be 0.48±0.19 and 0.31±0.15 respectively, with the former appearing to peak during the daytime because of a lack of PBA emission below the canopy.

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