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| Titel |
Characterising coarse PBA dynamics in real-time above and below a tropical rainforest canopy using a dual channel UV fluorescence aerosol spectrometer. |
| VerfasserIn |
A. Gabey, M. W. Gallagher, R. Burgess, H. Coe, G. McFiggans, P. H. Kaye, W. R. Stanley, F. Davies, V. E. Foot |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029967
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| Zusammenfassung |
| Primary biogenic aerosols (PBA) are used by organisms as a means to propagate
their genetic material, either by transport of the organisms themselves, such as
bacterial clusters and viruses, or of their reproductive components in the case of
fungi and plants that release spores and pollen. Many studies have suggested PBA
might be important for initiation of cloud formation and subsequent precipitation
evolution by acting as cloud condensation nuclei (CCN) or possibly as ice nuclei
(IN). This link is inferred from laboratory studies demonstrating the high activation
efficiency of PBA at warm temperatures, coupled with observations that biological
particles are ubiquitous in the atmosphere. Despite more than two hundred years of
research (e.g. Ehrenberg, 1830) information on the abundance, composition and
more importantly the sources and heterogeneity of PBA on global scales is still
lacking.
The first estimates of global average PBA emission rates based on observations and
budget calculations were provided by Elbert et al. (2007). They demonstrate that fungi
contribute a major fraction of the observed coarse PBA PM10 mass (particles with diameters
between 1-10 μ m), particularly Acomycota (AAM) and Basidiomycota (ABM) commonly
seen in tropical regions. These species discharge their spores via so-called “active wet”
mechanisms that eject spores inside liquid droplets. Elbert et al. (2007) estimate a global
average spore emission rate for ABM of ~17-50 Tg yr-1, corresponding to a global
average abundance of ~1 μg m-3 and a net emission rate for all fungal spores of
50 Tg yr-1. Uncertainty in the latter estimate is significant compared to the result, placed
at 50-1000 Tg yr-1. Nonetheless, these calculations demonstrate the potential
importance of PBA and particularly fungal spores in the tropics, where up to half of the
coarse mode particulate loading is PBA, and potentially in the global organic aerosol
budget.
Data was collected using the WIBS-3: a low-cost, portable single-particle dual channel
UV fluorescence spectrometer (Kaye et al., 2008) capable of detecting PBA by inducing
fluorescence in two so-called biofluorophores - one present during metabolism and the other
an amino acid - in the particle size range 1 μm < Dp < 20 μm. Real-time PBA
measurements were performed above and below the canopy of a tropical rainforest in Borneo,
Malaysia as part of the Oxidant and Particle Photochemical Processes (OP3) and the Aerosol
Coupling in the Earth System (ACES) projects. PBA were found to dominate the coarse
loading at Dp > 2 μm. In qualitative agreement with measurements of culturable
airborne material in a tropical forest’s understory (Gilbert, 2005) a diurnal cycle of
PBA number concentration is present, reaching a maximum of ~4000 l-1 at local
midnight and falling to ~100Â l-1 around midday. The role of the planetary boundary
layer’s collapse and re-establishment in dictating this variation in is also investigated
using LIDAR data. Transient PBA concentration spikes lasting several minutes are
superposed on the smooth underlying diurnal variation and occur at similar times
each day. Nucleopore filter samples were also taken in-situ and analysed under an
Environmental scanning electron microscope (ESEM) in Manchester. The images
obtained showed the PBA fraction to be dominated by fungal spores of diameter
2-5 μm, from various species including ABM. Since such species tend to release
spores in bursts at regular times this appears to account for the PBA concentration
spikes. |
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