Basic characteristics of atmospheric particles, trace gases and meteorology in a relatively clean Southern African Savannah environment L. Laakso1, H. Laakso1, P. P. Aalto1, P. Keronen1, T. Petäjä1,2, T. Nieminen1, T. Pohja1, E. Siivola1, M. Kulmala1, N. Kgabi3, M. Molefe3, D. Mabaso3, D. Phalatse4, K. Pienaar5, and V.-M. Kerminen6 1Department of Physical Sciences, University of Helsinki, P. O. BOX 64, 00014 Helsinki, Finland 2Earth and Sun Systems Laboratory, Atmospheric Chemistry Division, Nat. Center for Atmospheric Res., Boulder, CO, USA 3Department of Physics, North-West University, Private Bag X 2046, Mmabatho, South Africa 4Department of Biology, North-West University, Private Bag X 2046, Mmabatho, South Africa 5School of Chemistry, North-West University, Private Bag X 6001, Potchefstroom, South Africa 6Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
Abstract. We have analyzed one year (July 2006–July 2007) of measurement data from
a relatively clean background site located in dry savannah in South Africa.
The annual-median trace gas concentrations were equal to 0.7 ppb for
SO2, 1.4 ppb for NOx, 36 ppb for O3 and 105 ppb for CO. The
corresponding PM1, PM2.5 and PM10 concentrations were 9.0,
10.5 and 18.8 μg m−3, and the annual median total particle number
concentration in the size range 10–840 nm was 2340 cm−3. During
Easterly winds, influence of industrial sources approximately 150 km away
from the measurement site was clearly visible, especially in SO2 and
NOx concentrations. Of gases, NOx and CO had a clear annual, and
SO2, NOx and O3 clear diurnal cycle.
Atmospheric new-particle formation was observed to take place in more than
90% of the analyzed days. The days with no new particle formation were
cloudy or rainy days. The formation rate of 10 nm particles varied in the
range of 0.1–28 cm−3 s−1 (median 1.9 cm−3 s−1) and
nucleation mode particle growth rates were in the range 3–21 nm h−1
(median 8.5 nm h−1). Due to high formation and growth rates, observed
new particle formation gives a significant contribute to the number of cloud
condensation nuclei budget, having a potential to affect the regional
climate forcing patterns.
Citation: Laakso, L., Laakso, H., Aalto, P. P., Keronen, P., Petäjä, T., Nieminen, T., Pohja, T., Siivola, E., Kulmala, M., Kgabi, N., Molefe, M., Mabaso, D., Phalatse, D., Pienaar, K., and Kerminen, V.-M.: Basic characteristics of atmospheric particles, trace gases and meteorology in a relatively clean Southern African Savannah environment, Atmos. Chem. Phys., 8, 4823-4839, doi:10.5194/acp-8-4823-2008, 2008.