 |
| Titel |
Long-term observations of aerosol size distributions in semi-clean and polluted savannah in South Africa |
| VerfasserIn |
V. Vakkari, J. P. Beukes, H. Laakso  , D. Mabaso, J. J. Pienaar, M. Kulmala , L. Laakso |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 4 ; Nr. 13, no. 4 (2013-02-15), S.1751-1770 |
| Datensatznummer |
250017658
|
| Publikation (Nr.) |
 copernicus.org/acp-13-1751-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
This study presents a total of four years of sub-micron aerosol particle
size distribution measurements in the southern African savannah, an
environment with few previous observations covering a full seasonal cycle
and the size range below 100 nm. During the first 19 months, July 2006–January 2008,
the measurements were carried out at Botsalano, a semi-clean
location, whereas during the latter part, February 2008–May 2010, the
measurements were carried out at Marikana (approximately 150 km east of
Botsalano), which is a more polluted location with both pyrometallurgical
industries and informal settlements nearby.
The median total concentration of aerosol particles was more than four times
as high at Marikana than at Botsalano. In the size ranges of 12–840 nm,
50–840 nm and 100–840 nm the median concentrations were 1856, 1278 and
698 particles cm−3 at Botsalano and 7805, 3843 and
1634 particles cm−3 at Marikana, respectively.
The diurnal variation of the size distribution for Botsalano arose as a
result of frequent regional new particle formation. However, for Marikana
the diurnal variation was dominated by the morning and evening household
burning in the informal settlements, although regional new particle
formation was even more frequent than at Botsalano. The effect of the
industrial emissions was not discernible in the size distribution at
Marikana although it was clear in the sulphur dioxide diurnal pattern,
indicating the emissions to be mostly gaseous.
Seasonal variation was strongest in the concentration of particles larger
than 100 nm, which was clearly elevated at both locations during the dry
season from May to September. In the absence of wet removal during the dry
season, the concentration of particles larger than 100 nm had a correlation
above 0.7 with CO for both locations, which implies incomplete burning to be
an important source of aerosol particles during the dry season. However, the
sources of burning differ: at Botsalano the rise in concentration originates
from regional wild fires, while at Marikana domestic heating in the informal
settlements is the main source.
Air mass history analysis for Botsalano identified four regional scale
source areas in southern Africa and enabled the differentiation between
fresh and aged rural background aerosol originating from the clean sector,
i.e., western sector with very few large anthropogenic sources. Comparison to
size distributions published for other comparable environments in Northern
Hemisphere shows southern African savannah to have a unique combination of
sources and meteorological parameters. The observed strong link between
combustion and seasonal variation is comparable only to the Amazon basin;
however, the lack of long-term observations in the Amazonas does not allow a
quantitative comparison.
All the data presented in the figures, as well as the time series of monthly
mean and median size distributions are included in numeric form as a
Supplement to provide a reference point for the aerosol modelling community. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|