Atmos. Chem. Phys. Discuss., 12, 1895-1934, 2012
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Characterisation of sub-micron particle number concentrations and formation events in the western Bushveld Igeneous Complex, South Africa
A. Hirsikko1,2, V. Vakkari2, P. Tiitta3,4, H. E. Manninen2, S. Gagné2,*, H. Laakso2, M. Kulmala2, A. Mirme5, S. Mirme5, D. Mabaso6, J. P. Beukes4, and L. Laakso1,2,4
1Finnish Meteorological Institute, Research and Development, P.O. Box 503, 00101, Finland
2Department of Physics, Univ. of Helsinki, P.O. Box 64, 00014 Univ. of Helsinki, Finland
3University of Eastern Finland, PL 1627, 70211 Kuopio, Finland
4School of Physical and Chemical Sciences, North-West Univ., Potchefstroom, South Africa
5Institute of Physics, University of Tartu, 18 Ülikooli Str., 50090 Tartu, Estonia
6Rustenburg Local Municipality, Rustenburg, South Africa
*now at: Dalhousie University and Environment, Canada

Abstract. South Africa holds significant mineral resources, with a substantial fraction of these reserves occurring in a large geological structure termed the Bushveld Igeneous Complex (BIC). The majority of the world's platinum group metals (PGMs) and chromium originate from the BIC. Considering the importance of PGMs in the manufacturing of automotive catalytic converters, as well as the relatively poor current state of air quality and the general lack of atmospheric research in the BIC, atmospheric related research in this geographical area is of local (South African) and of international interest. The western limb of the BIC is the most exploited, with at least eleven pyrometallurgical smelters occurring within a 55 km radius. Due to the lure of employment in the industrialised BIC, the area is populated by informal, semi-formal and formal residential developments. In order to investigate the characteristics and processes affecting sub-micron particle number concentrations and formation events, air ion and aerosol particle size distribution and concentration measurements were conducted for over two years at Marikana in the heart of the western BIC. Our results indicated that high amounts of Aitken and accumulation mode particles originated from domestic burning for heating and cooking in the morning and evening, while during daytime SO2-based nucleation (from industrial emissions) was the most probable source for large number concentrations of nucleation and Aitken mode particles. Nucleation event day frequency was extremely high, i.e. 86% of the analysed days, which to the knowledge of the authors is the highest frequency ever reported. Secondary particle formation was influenced both by local pollution sources and regional ambient conditions. Therefore, our observation of the annual cycle and magnitude of the particle formation and growth rates during nucleation events were similar to the results from a semi-clean savannah site in South Africa.

Citation: Hirsikko, A., Vakkari, V., Tiitta, P., Manninen, H. E., Gagné, S., Laakso, H., Kulmala, M., Mirme, A., Mirme, S., Mabaso, D., Beukes, J. P., and Laakso, L.: Characterisation of sub-micron particle number concentrations and formation events in the western Bushveld Igeneous Complex, South Africa, Atmos. Chem. Phys. Discuss., 12, 1895-1934, doi:10.5194/acpd-12-1895-2012, 2012.
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