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| Titel |
On the diurnal cycle of urban aerosols, black carbon and the occurrence of new particle formation events in springtime São Paulo, Brazil |
| VerfasserIn |
J. Backman, L. V. Rizzo, J. Hakala, T. Nieminen, H. E. Manninen, F. Morais, P. P. Aalto, E. Siivola, S. Carbone, R. Hillamo, P. Artaxo, A. Virkkula, T. Petäjä, M. Kulmala  |
| 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. 23 ; Nr. 12, no. 23 (2012-12-11), S.11733-11751 |
| Datensatznummer |
250011657
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| Publikation (Nr.) |
 copernicus.org/acp-12-11733-2012.pdf |
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| Zusammenfassung |
| Large conurbations are a significant source of the anthropogenic pollution
and demographic differences between cities that result in a different pollution
burden. The metropolitan area of São Paulo (MASP, population 20 million)
accounts for one fifth of the Brazilian vehicular fleet. A feature of MASP
is the amount of ethanol used by the vehicular fleet, known to exacerbate
air quality. The study describes the diurnal behaviour of the submicron
aerosol and relies on total particle number concentration, particle number
size distribution, light scattering and light absorption measurements.
Modelled planetary boundary layer (PBL) depth and air mass movement data
were used to aid the interpretation. During morning rush-hour, stagnant air
and a shallow PBL height favour the accumulation of aerosol pollution.
During clear-sky conditions, there was a wind shift towards the edge of the
city indicating a heat island effect with implications on particulate
pollution levels at the site. The median total particle number concentration
for the submicron aerosol typically varied in the range 1.6 × 104–3.2 × 104 cm−3 frequently exceeding
4 × 104 cm−3 during the day. During weekdays,
nucleation-mode particles are responsible for most of the particles by
numbers. The highest concentrations of total particle number concentrations
and black carbon (BC) were observed on Fridays. Median diurnal values for
light absorption and light scattering (at 637 nm wavelength) varied in the
range 12–33 Mm−1 and 21–64 Mm−1, respectively. The former
one is equal to 1.8–5.0 μg m−3 of BC. The growth of the PBL,
from the morning rush-hour until noon, is consistent with the diurnal cycle
of BC mass concentrations. Weekday hourly median single-scattering albedo
(ω0) varied in the range 0.59–0.76. Overall, this suggests a
top of atmosphere (TOA) warming effect. However, considering the low surface
reflectance of urban areas, for the given range of ω0, the TOA
radiative forcing can be either positive or negative for the sources within
the MASP. On the average, weekend ω0 values were 0.074 higher
than during weekdays. During 11% of the days, new particle formation
(NPF) events occurred. The analysed events growth rates ranged between 9 and
25 nm h−1. Sulphuric acid proxy concentrations calculated for the site
were less than 5% of the concentration needed to explain the observed
growth. Thus, other vapours are likely contributors to the observed growth. |
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