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| Titel |
Impact of Manaus City on the Amazon Green Ocean atmosphere: ozone production, precursor sensitivity and aerosol load |
| VerfasserIn |
U. Kuhn, L. Ganzeveld, A. Thielmann, T. Dindorf, G. Schebeske, M. Welling, J. Sciare, G. Roberts, F. X. Meixner, J. Kesselmeier, J. Lelieveld  , O. Kolle, P. Ciccioli, J. Lloyd, J. Trentmann, P. Artaxo, M. O. Andreae |
| 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 (2010-10-01), S.9251-9282 |
| Datensatznummer |
250008800
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| Publikation (Nr.) |
 copernicus.org/acp-10-9251-2010.pdf |
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| Zusammenfassung |
As a contribution to the Large-Scale Biosphere-Atmosphere Experiment in
Amazonia – Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001)
field campaign in the heart of the Amazon Basin, we analyzed the temporal
and spatial dynamics of the urban plume of Manaus City during the
wet-to-dry season transition period in July 2001. During the flights, we
performed vertical stacks of crosswind transects in the urban outflow
downwind of Manaus City, measuring a comprehensive set of trace constituents
including O3, NO, NO2, CO, VOC, CO2, and H2O. Aerosol loads were characterized by
concentrations of total aerosol number (CN) and cloud condensation nuclei (CCN),
and by light scattering properties. Measurements over pristine rainforest areas during the campaign
showed low levels of pollution from biomass burning or industrial emissions,
representative of wet season background conditions. The urban plume of
Manaus City was found to be joined by plumes from power plants south of the
city, all showing evidence of very strong photochemical ozone formation. One
episode is discussed in detail, where a threefold increase in ozone mixing
ratios within the atmospheric boundary layer occurred within a 100 km travel
distance downwind of Manaus. Observation-based estimates of the ozone
production rates in the plume reached 15 ppb h−1.
Within the plume core, aerosol concentrations were strongly enhanced, with
ΔCN/ΔCO ratios about one order of magnitude higher than
observed in Amazon biomass burning plumes. ΔCN/ΔCO ratios
tended to decrease with increasing transport time, indicative of a
significant reduction in particle number by coagulation, and without
substantial new particle nucleation occurring within the time/space
observed. While in the background atmosphere a large fraction of the total
particle number served as CCN (about 60–80% at 0.6% supersaturation),
the CCN/CN ratios within the plume indicated that only a small fraction
(16±12%) of the plume particles were CCN. The fresh plume aerosols
showed relatively weak light scattering efficiency. The CO-normalized CCN
concentrations and light scattering coefficients increased with plume age in
most cases, suggesting particle growth by condensation of soluble organic or
inorganic species.
We used a Single Column Chemistry and Transport Model (SCM) to infer the
urban pollution emission fluxes of Manaus City, implying observed mixing
ratios of CO, NOx and VOC. The model can reproduce the temporal/spatial
distribution of ozone enhancements in the Manaus plume, both with and
without accounting for the distinct (high NOx) contribution by the
power plants; this way examining the sensitivity of ozone production to
changes in the emission rates of NOx. The VOC reactivity in the Manaus
region was dominated by a high burden of biogenic isoprene from the
background rainforest atmosphere, and therefore NOx control is assumed
to be the most effective ozone abatement strategy. Both observations and
models show that the agglomeration of NOx emission sources, like power
plants, in a well-arranged area can decrease the ozone production efficiency
in the near field of the urban populated cores. But on the other hand remote
areas downwind of the city then bear the brunt, being exposed to increased
ozone production and N-deposition. The simulated maximum stomatal ozone
uptake fluxes were 4 nmol m−2 s−1 close to Manaus, and decreased
only to about 2 nmol m−2 s−1 within a travel distance >1500 km
downwind from Manaus, clearly exceeding the critical threshold level for
broadleaf trees. Likewise, the simulated N deposition close to Manaus was
~70 kg N ha−1 a−1 decreasing only to about
30 kg N ha−1 a−1 after three days of simulation. |
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