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| Titel |
Time evolution and emission factors of aerosol particles from day and night time savannah fires |
| VerfasserIn |
Ville Vakkari, Johan Paul Beukes, Petri Tiitta, Andrew Venter, Kerneels Jaars, Miroslav Josipovic, Pieter Van Zyl, Markku Kulmala  , Lauri Laakso |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080810
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| Zusammenfassung |
| The largest uncertainties in the current global climate models originate from aerosol particle
effects (IPCC, 2007) and at the same time aerosol particles also pose a threat to human health
(Pope and Dockery, 2006). In southern Africa wild fires and prescribed burning are one of
the most important sources of aerosol particles, especially during the dry season
from June to September (e.g. Swap et al., 2003; Vakkari et al., 2012). The aerosol
particle emissions from savannah fires in southern Africa have been studied in several
intensive campaigns such as SAFARI 1992 and 2000 (Swap et al., 2003). However, all
previous measurements have been carried out during the daytime, whereas most of the
prescribed fires in southern Africa are lit up only after sunset. Furthermore, the
previous campaigns followed the plume evolution for up to one hour after emission
only.
In this study, combining remote sensing fire observations to ground-based long-term
measurements of aerosol particle and trace gas properties at the Welgegund measurement
station (www.welgegund.org), we have been able to follow the time evolution of savannah
fire plumes up to several hours in the atmosphere. For the first time the aerosol particle size
distribution measurements in savannah fire plumes cover both day and night time plumes and
also the ultrafine size range below 100 nm.
During the period from May 20th 2010 to April 15th 2012 altogether 61 savannah fire
plumes were observed at Welgegund. The evolution of the aerosol size distribution remained
rapid for at least five hours after the fire: during this period the growth rate of the
aerosol particle count mean diameter (size range 12 to 840 nm) was 24 nm h-1 for
daytime plumes and 8 nm h-1 for night time plumes. The difference in the day and
night time growth rate shows that photochemical reactions significantly increase
the condensable vapour concentration in the plume. Furthermore, the condensable
vapour concentration was found to affect both the number and size of particles
larger than 100 nm; if this is not accounted for the current emission factors may
underestimate the CCN-sized particle yield from savannah fires by a factor of two to
three.
Acknowledgements
This research was supported by the Academy of Finland under the project Atmospheric
monitoring capacity building in Southern Africa (project number 132640), by the
Saastamoinen säätiö, by the North-West University and by the Academy of Finland Center of
Excellence program (project number 1118615).
References
IPCC, Climate Change 2007: The Physical Science Basis. Contribution of Working
Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change,
Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA,
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Pope, C. A., and Dockery, D. W.: Health effects of fine particulate air pollution: lines that
connect, J Air Waste Manag. Assoc., 56, 709-742, 2006.
Swap, R. J., Annegarn, H. J., Suttles, J. T., King, M. D., Platnick, S., Privette, J. L., and
Scholes, R. J.: Africa burning: A thematic analysis of the Southern African Regional Science
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Vakkari, V., Beukes, J. P., Laakso, H., Mabaso, D., Pienaar, J. J., Kulmala, M., and
Laakso, L.: Long-term observations of aerosol size distributions in semi-clean and
polluted savannah in South Africa, Atmos. Chem. Phys. Discuss., 12, 24043-24093,
doi:10.5194/acpd-12-24043-2012, 2012. |
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