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| Titel |
The composition and variability of atmospheric aerosol over Southeast Asia during 2008 |
| VerfasserIn |
W. Trivitayanurak, P. I. Palmer, M. P. Barkley, N. H. Robinson, H. Coe, D. E. Oram |
| 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 ; 12, no. 2 ; Nr. 12, no. 2 (2012-01-26), S.1083-1100 |
| Datensatznummer |
250010549
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| Publikation (Nr.) |
 copernicus.org/acp-12-1083-2012.pdf |
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| Zusammenfassung |
| We use a nested version of the GEOS-Chem global 3-D chemistry
transport model to better understand the composition and variation of
aerosol over Borneo and the broader Southeast Asian region in
conjunction with aircraft and satellite observations. Our focus on
Southeast Asia reflects the importance of this region as a source of
reactive organic gases and aerosols from natural forests, biomass
burning, and food and fuel crops. We particularly focus on July 2008
when the UK BAe-146 research aircraft was deployed over
northern Malaysian Borneo as part of the ACES/OP3 measurement
campaign. During July 2008 we find using the model that Borneo
(defined as Borneo Island and the surrounding Indonesian islands) was
a net exporter of primary organic aerosol (42 kT) and black carbon
aerosol (11 kT). We find only 13% of volatile organic compound
oxidation products partition to secondary organic aerosol (SOA), with
Borneo being a net exporter of SOA (15 kT). SOA represents
approximately 19% of the total organic aerosol over the region.
Sulphate is mainly from aqueous-phase oxidation (68%), with
smaller contributions from gas-phase oxidation (15%) and
advection into the regions (14%). We find that there is a large
source of sea salt, as expected, but this largely deposits within the
region; we find that dust aerosol plays only a relatively small role
in the aerosol burden. In contrast to coincident surface measurements
over Northern Borneo that find a pristine environment with evidence
for substantial biogenic SOA formation we find that the free
troposphere is influenced by biomass burning aerosol transported from
the northwest of the Island and further afield. We find several
transport events during July 2008 over Borneo associated with elevated
aerosol concentrations, none of which coincide with the aircraft
flights. We use MODIS aerosol optical depths (AOD) data and the model
to put the July campaign into a longer temporal perspective. We find
that Borneo is where the model has the least skill at reproducing the
data, where the model has a negative bias of 76% and only captures
14% of the observed variability. This model performance reflects the
small-scale island-marine environment and the mix of aerosol species,
with the model showing more skill at reproducing observed AOD over
larger continental regions such as China where AOD is dominated by one
aerosol type. The model shows that AOD over Borneo is approximately
evenly split between organic and sulphate aerosol with sea salt
representing 10–20% during May–September; we find a similar breakdown
over continental Southeast Asia but with less sea salt aerosol and
more dust aerosol. In contrast, East China AOD is determined mainly by
sulphate aerosol and a seasonal source of dust aerosol, as
expected. Realistic sensitivity runs, designed to test our underlying
assumptions about emissions and chemistry over Borneo, show that model
AOD is most sensitive to isoprene emissions and organic gas-phase
partitioning but all fail to improve significantly upon the control
model calculation. This emphasises the multi-faceted dimension of the
problem and the need for concurrent and coordinated development of
BVOC emissions, and BVOC chemistry and organic aerosol formation
mechanisms. |
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