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| Titel |
Source apportionment of carbonaceous aerosol in Sao Paulo using 13C and 14C measurements |
| VerfasserIn |
Beatriz Oyama, Maria de Fatima Andrade, Rupert Holzinger, Thomas Röckmann, Harro A. J. Meijer, Ulrike Dusek |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133395
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| Publikation (Nr.) |
 EGU/EGU2016-14001.pdf |
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| Zusammenfassung |
| The Metropolitan Area of Sao Paulo is affected by high aerosol concentrations,
which contain a large fraction of organic material. Up to date, not much is known
about the composition and origin of the organic aerosol in this city. We present
the first source apportionment of the carbonaceous aerosol fraction in Sao Paulo,
using stable (13C) and radioactive carbon isotopes (14C). 14C provides a clear-cut
distinction between fossil sources, which contain no 14C, and contemporary sources
such as biofuels, biomass burning, or biogenic sources, which contain a typical
contemporary 14C/12C ratio. 13C can be used to distinguish C3 plants, such as
maize and sugarcane, from C4 plants. This can help to identify a possible impact of
sugarcane field burning in the rural areas of Sao Paulo State on the aerosol carbon in the
city.
In the first part of the study, we compare two tunnel studies: Tunnel 1 is frequented only
by light duty vehicles, which run mainly on mixtures of gasoline with ethanol (gasohol, 25%
ethanol and 85% gasoline) or hydrated ethanol (5% water and 95% ethanol). Tunnel 2
contains a significant fraction of heavy-duty diesel vehicles, and therefore the fraction of
biofuels in the average fleet is lower. Comparison of 14C in organic and elemental carbon
(OC and EC) shows that in both tunnels there is no significant contribution of biofuels to EC.
Combusting ethanol-gasoline fuels in a vehicle engine does apparently not result in
significant EC formation from ethanol. Biofuels contribute around 45% to OC in Tunnel 1
an only 20% in Tunnel 2, reflecting a strong impact of diesel vehicles in Tunnel
2.
In the second part of the study we conduct a source apportionment of ambient
aerosol carbon collected in a field study during winter (July-August) 2012. Ambient
EC has two main sources, vehicular emissions and biomass burning. We estimate
a contribution of vehicular sources to EC of roughly 90% during weekdays and
80% during weekends, using the 14C values measured in the tunnel studies. The
absolute concentration of biomass burning EC is roughly 0.5 μg/m3 both during
weekend and weekdays, whereas vehicular EC concentrations almost double during
weekdays, increasing from 1.8 to 3.7 μg/m3 on average. OC concentrations are
dominated by secondary carbon from vehicular emissions, both on weekdays and
during weekends, however primary OC from biomass burning and contemporary
secondary OC (from both biogenic and biomass burning emissions) are important
fractions as well. Overall, primary biomass burning contributes between 10 and 30% to
the carbonaceous aerosol in Sao Paulo. 13C measurements indicate that sugarcane
burning could account for up to 15% of OC in the Sao Paulo metropolitan area. |
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