ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-3951-2012 Characterisation of sub-micron particle number concentrations and formation events in the western Bushveld Igneous Complex, South Africa Hirsikko A. 1 2 Vakkari V. 2 Tiitta P. 3 4 Manninen H. E. 2 Gagné S. 2 7 8 Laakso H. 2 Kulmala M. 2 Mirme A. 5 Mirme S. 5 Mabaso D. 6 Beukes J. P. 4 Laakso L. 1 4 Finnish Meteorological Institute, Research and Development, P.O. Box 503, 00101, Finland Department of Physics, University of Helsinki, P.O. Box 64, University of Helsinki, 00014, Finland University of Eastern Finland, PL 1627, 70211, Kuopio, Finland School of Physical and Chemical Sciences, North-West University, Potchefstroom, South Africa Institute of Physics, University of Tartu, 18 Ülikooli Str., 50090 Tartu, Estonia Rustenburg Local Municipality, Rustenburg, South Africa now at: Environment Canada, Toronto, Ontario, M3H5T4, Canada now at: Dalhousie University, Halifax, Nova Scotia, B3H3J5, Canada 04 05 2012 12 9 3951 3967 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/3951/2012/acp-12-3951-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/3951/2012/acp-12-3951-2012.pdf

South Africa holds significant mineral resources, with a substantial fraction of these reserves occurring and being processed in a large geological structure termed the Bushveld Igneous Complex (BIC). The area is also highly populated by informal, semi-formal and formal residential developments. However, knowledge of air quality and research related to the atmosphere is still very limited in the area. In order to investigate the characteristics and processes affecting sub-micron particle number concentrations and formation events, air ion and aerosol particle size distributions and number concentrations, together with meteorological parameters, trace gases and particulate matter (PM) were measured for over two years at Marikana in the heart of the western BIC. The observations showed that trace gas (i.e. SO<sub>2</sub>, NO<sub>x</sub>, CO) and black carbon concentrations were relatively high, but in general within the limits of local air quality standards. The area was characterised by very high condensation sink due to background aerosol particles, PM<sub>10</sub> and O<sub>3</sub> concentration. The 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 SO<sub>2</sub>-based nucleation followed by the growth by condensation of vapours from industrial, residential and natural sources 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. The air mass back trajectory and wind direction analyses showed that the secondary particle formation was influenced both by local and regional pollution and vapour sources. Therefore, our observation of the annual cycle and magnitude of the particle formation and growth rates during nucleation events were similar to results previously published for a semi-clean savannah site in South Africa.

 References Air Resources Laboratory: Gridded Meteorological Data Archives, available at: http://www.arl.noaa.gov/archives.php, 2011. Asmi, E., Frey, A., Virkkula, A., Ehn, M., Manninen, H. E., Timonen, H., Tolonen-Kivimäki, O., Aurela, M., Hillamo, R., and Kulmala, M.: Hygroscopicity and chemical composition of Antarctic sub-micrometre aerosol particles and observations of new particle formation, Atmos. Chem. Phys., 10, 4253–4271, http://dx.doi.org/10.5194/acp-10-4253-2010doi:10.5194/acp-10-4253-2010, 2010. Asmi, E., Kivekäs, N., Kerminen, V.-M., Komppula, M., Hyvärinen, A.-P., Hatakka, J., Viisanen, Y., and Lihavainen, H.: Secondary new particle formation in Northern Finland Pallas site between the years 2000 and 2010, Atmos. Chem. Phys., 11, 12959–12972, http://dx.doi.org/10.5194/acp-11-12959-2011doi:10.5194/acp-11-12959-2011, 2011. Beukes, J. P., Dawson, N. F., and Van Zyl, P. G.: Theoretical and practical aspects of Cr(VI) in the South African FeCr industry, S. African Inst. Min. M., 110, 743–750, 2010. Breitner, S., Liu, L., Cyrys, J., Brüske, I., Franck, U., Schlink, U., Leitte, A.M., Herbath, O., Wiedensohler, A., Wehner, B., Hu, M., Pan, X.-C., Wichmann, H.-E., and Peters, A.: Sub-micrometer particulate air ion pollution and cardiovascular mortality in Beijing, China, Sci. Total Environ., 409, 5196–5204, 2011. Brus, D., Neitola, K., Hyvärinen, A.-P., Petäjä, T., Vanhanen, J., Sipilä, M., Paasonen, P., Kulmala, M., and Lihavainen, H.: Homogenous nucleation of sulfuric acid and water at close to atmospherically relevant conditions, Atmos. Chem. Phys., 11, 5277–5287, http://dx.doi.org/10.5194/acp-11-5277-2011doi:10.5194/acp-11-5277-2011, 2011. Cheung, H. C., Morawska, L., and Ristovski, Z. D.: Observation of new particle formation in subtropical urban environment, Atmos. Chem. Phys., 11, 3823–3833, http://dx.doi.org/10.5194/acp-11-3823-2011doi:10.5194/acp-11-3823-2011, 2011. Curtius, J., Lovejoy, E. R., and Froyd, K. D.: Atmospheric ion induced aerosol nucleation, Space Sci. Rev., 125, 159–167, 2006. Cramer, L. A., Basson, J., and Nelson, L. R.: The impact of platinum production from UG2 ore on ferrochrome production in South African, S. African Inst. Min. M., 104, 517–527, 2004. Dal Maso, M., Kulmala, M., Riipinen, I., Wagner, R., Hussein, T., Aalto, P. P., and Lehtinen, K. E. J.: Formation and growth of fresh atmospheric aerosols: eight years of aerosol size distribution data from SMEAR II, Hyytiälä, Finland, Boreal Environ. Res., 10, 323–336, 2005. Dal Maso, M., Sogacheva, L., Aalto, P.P., Riipinen, I., Komppula, M., Tunved, P., Korhonen, L., Suur-Uski, V., Hirsikko, A., Kurtén, T., Kerminen, V.-M., Lihavainen, H., Viisanen, Y., Hansson, H.-C., and Kulmala, M.: Aerosol size distribution measurements at four Nordic field stations: identification, analysis, and trajectory analysis of new particle formation bursts, Tellus, 59B, 350-361, 2007. Draxler, R. R. and Hess, G. D.: Description of the HYSPLIT 4 Modelling System, NOAA Technical Memorandum ERL ARL-224, 2004. Dunn, M. J., Jiménez, J.-L., Baumgardner, D., Castro, T., McMurry, P. H., and Smith, J. N.: Measurements of Mexico City nanoparticle size distributions: Observations of new particle formation and growth, Geophys. Res. Lett., 31, L01012, http://dx.doi.org/10.1029/2004GL019483doi:10.1029/2004GL019483, 2004. Fiedler, V., Dal Maso, M., Boy, M., Aufmhoff, H., Hoffmann, J., Schuck, T., Birmili, W., Hanke, M., Uecker, J., Arnold, F., and Kulmala, M.: The contribution of sulphuric acid to atmospheric particle formation and growth: a comparison between boundary layers in Northern and Central Europe, Atmos. Chem. Phys., 5, 1773–1785, http://dx.doi.org/10.5194/acp-5-1773-2005doi:10.5194/acp-5-1773-2005, 2005. Gagné, S., Lehtipalo, K., Manninen, H. E., Nieminen, T., Schobesberger, S., Franchin, A., Yli-Juuti, T., Boulon, J., Sonntag, A., Mirme, S., Mirme, A., Hõrrak, U., Petäjä, T., Asmi, E., and Kulmala, M.: Intercomparison of air ion spectrometers: an evaluation of results in varying conditions, Atmos. Meas. Tech., 4, 805–822, http://dx.doi.org/10.5194/amt-4-805-2011doi:10.5194/amt-4-805-2011, 2011. Garstang, M., Tyson, P. D., Swap, R., Edwards, M., Kållberg, P., and Lindesay, J. A.: Horizontal and vertical transport of air over southern Africa, J. Geophys. Res., 101, 721–736, 1996. Hand, J. L. and Malm, W. C.: Review of aerosol mass scattering efficiencies from ground-based measurements since 1990, J. Geophys. Res., 112, D16203, http://dx.doi.org/10.1029/2007JD008484doi:10.1029/2007JD008484, 2007. Hirsikko, A., Laakso, L., Hõrrak, U., Aalto, P., Kerminen, V., and Kulmala, M.: Annual and size dependent variation of growth rates and ion concentrations in boreal forest, Boreal Environ. Res., 10, 357–369, 2005. Hirsikko, A., Bergman, T., Laakso, L., Dal Maso, M., Riipinen, I., Hõrrak, U., and Kulmala, M.: Identification and classification of the formation of intermediate ions measured in boreal forest, Atmos. Chem. Phys., 7, 201–-210, http://dx.doi.org/10.5194/acp-7-201-2007doi:10.5194/acp-7-201-2007, 2007a. Hirsikko, A., Yli-Juuti, T., Nieminen, T., Vartiainen, E., laakso, L., Hussein, T., and Kulmala: Indoor and outdoor air ions and aerosol particles in the uban atmosphere of Helsinki: characteristics, sources and formation, Boreal Eviron. Res., 12, 295–310, 2007b. Hirsikko, A., Nieminen, T., Gagné, S., Lehtipalo, K., Manninen, H. E., Ehn, M., Hõrrak, U., Kerminen, V.-M., Laakso, L., McMurry, P. H., Mirme, A., Mirme, S., Petäjä, T., Tammet, H., Vakkari, V., Vana, M., and Kulmala, M.: Atmospheric ions and nucleation: a review of observations, Atmos. Chem. Phys., 11, 767–798, http://dx.doi.org/10.5194/acp-11-767-2011doi:10.5194/acp-11-767-2011, 2011. Hoppel, W. A.: Determination of the aerosol size distribution from the mobility distribution of the charged fraction of aerosols, J. Aerosol Sci., 9, 41–54, 1978. Hussein, T., Puustinen, A., Aalto, P. P., Mäkelä, J. M., Hämeri, K., and Kulmala, M.: Urban aerosol number size distributions, Atmos. Chem. Phys., 4, 391–411, http://dx.doi.org/10.5194/acp-4-391-2004doi:10.5194/acp-4-391-2004, 2004. Hussein, T., Dal Maso, M., Petäjä, T., Koponen, I. K., Paatero, P., Aalto, P. P., Hämeri, K., and Kulmala, M.: Evaluation of an automatic algorithm for fitting the particle number size distributions, Boreal Environ. Res., 10, 337–355, 2005. Iida, K., Stolzenburg, M., McMurry, P., Dunn, M. J., Smith, J. N., Eisele, F., and Keady, P.: Contribution of ion-induced nucleation to new particle formation: Methodology and its application to atmospheric observations in Boulder, Colorado, J. Geophys. Res., 111, D23201, http://dx.doi.org/10.1029/2006JD007167doi:10.1029/2006JD007167, 2006. Iida, K., Stolzenburg, M. R., McMurry, P. H., and Smith, J. N.: Estimating nanoparticle growth rates from \mboxsize-dependent charged fractions: Analysis of new particle formation events in Mexico City, J. Geophys. Res., 113, D05207, http://dx.doi.org/10.1029/2007JD009260doi:10.1029/2007JD009260, 2008. IPCC: Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), 2007. Jaatinen, A., Hamed, A., Joutsensaari, J., Mikkonen, S., Birmili, W., Wehner, B., Spindler, G., Wiedensohler, A., Decasari, S., Mircea, M., Facchini, M. C., Junninen, H., Kulmala, M., Lehtinen, K. E. J., and Laaksonen, A.: A comparison of new particle formation events in the boundary layer at three different sites in Europe, Boreal Environ. Res., 14, 481–498, 2009. Jayaratne, E. R. and Verma, T. S.: The impact of biomass burning on the environmental aerosol concentration in Gaborone, Botswana, Atmos. Environ., 35, 1821–1828, 2001. Jokinen, V. and Mäkelä, J. M.: Closed loop arrangement with critical orifice for DMA sheath/excess flow system, J. Aerosol Sci., 28, 643–648, 1997. Junninen, H., Hulkkonen, M., Riipinen, I., Nieminen, T., Hirsikko, A., Suni, T., Boy, M., Lee, S.-H., Vana, M., Tammet, H., Kerminen, V.-M., and Kulmala, M.: Observations on nocturnal growth of atmospheric clusters, Tellus, 60B, 365–371, 2008. Kalafut-Pettibone, A. J., Wang, J., Eichinger, W. E., Clarke, A., Vay, S. A., Blake, D. R., and Stanier, C. O.: Size-resolved aerosol emission factors and new particle formation/growth activity occurring in Mexico City during the MILAGRO 2006 Campaign, Atmos. Chem. Phys., 11, 8861–8881, http://dx.doi.org/10.5194/acp-11-8861-2011doi:10.5194/acp-11-8861-2011, 2011. Kuang, C., McMurry, P. H., McCormick, A. V., and Eisele, F. L.: Dependence of nucleation rates on sulphuric acid vapor concentrations in diverse atmospheric locations, J. Geophys. Res., 113, D10209, http://dx.doi.org/10.1029/2007JD009253doi:10.1029/2007JD009253, 2008. Kulmala, M., Vehkamäki, H., Petäjä, T., Dal Maso, M., Lauri, A., Kerminen, V.-M., Birmili, W., and McMurry, P. H.: Formation and growth rates of ultrafine atmospheric particles: a review of observations, J. Aerosol Sci., 35, 143–176, 2004. Kulmala, M., Petäjä, T., Mönkkönen, P., Koponen, I. K., Dal Maso, M., Aalto, P. P., Lehtinen, K. E. J., and Kerminen, V.-M.: On the growth of nucleation mode particles: source rates of condensable vapor in polluted and clean environments, Atmos. Chem. Phys., 5, 409–416, http://dx.doi.org/10.5194/acp-5-409-2005doi:10.5194/acp-5-409-2005, 2005. Kulmala, M., Riipinen, I., Sipilä, M., Manninen, H. E., Petäjä, T., Junninen, H., Dal Maso, M., Mordas, G., Mirme, A., Vana, M., Hirsikko, A., Laakso, L., Harrison, R. M., Hanson, I., Leung, C., Lehtinen, K. E. J., and Kerminen, V.-M.: Toward direct measurement of atmospheric nucleation, Science, 318, 89–92, 2007. Kulmala, M., Asmi, A., Lappalainen, H. K., Baltensperger, U., Brenguier, J.-L., Facchini, M. C., Hansson, H.-C., Hov, Ø., O'Dowd, C. D., Pöschl, U., Wiedensohler, A., Boers, R., Boucher, O., de Leeuw, G., Denier van der Gon, H. A. C., Feichter, J., Krejci, R., Laj, P., Lihavainen, H., Lohmann, U., McFiggans, G., Mentel, T., Pilinis, C., Riipinen, I., Schulz, M., Stohl, A., Swietlicki, E., Vignati, E., Alves, C., Amann, M., Ammann, M., Arabas, S., Artaxo, P., Baars, H., Beddows, D. C. S., Bergström, R., Beukes, J. P., Bilde, M., Burkhart, J. F., Canonaco, F., Clegg, S. L., Coe, H., Crumeyrolle, S., D'Anna, B., Decesari, S., Gilardoni, S., Fischer, M., Fjaeraa, A. M., Fountoukis, C., George, C., Gomes, L., Halloran, P., Hamburger, T., Harrison, R. M., Herrmann, H., Hoffmann, T., Hoose, C., Hu, M., Hyvärinen, A., Hõrrak, U., Iinuma, Y., Iversen, T., Josipovic, M., Kanakidou, M., Kiendler-Scharr, A., Kirkevåg, A., Kiss, G., Klimont, Z., Kolmonen, P., Komppula, M., Kristjánsson, J.-E., Laakso, L., Laaksonen, A., Labonnote, L., Lanz, V. A., Lehtinen, K. E. J., Rizzo, L. V., Makkonen, R., Manninen, H. E., McMeeking, G., Merikanto, J., Minikin, A., Mirme, S., Morgan, W. T., Nemitz, E., O'Donnell, D., Panwar, T. S., Pawlowska, H., Petzold, A., Pienaar, J. J., Pio, C., Plass-Duelmer, C., Prévôt, A. S. H., Pryor, S., Reddington, C. L., Roberts, G., Rosenfeld, D., Schwarz, J., Seland, Ø., Sellegri, K., Shen, X. J., Shiraiwa, M., Siebert, H., Sierau, B., Simpson, D., Sun, J. Y., Topping, D., Tunved, P., Vaattovaara, P., Vakkari, V., Veefkind, J. P., Visschedijk, A., Vuollekoski, H., Vuolo, R., Wehner, B., Wildt, J., Woodward, S., Worsnop, D. R., van Zadelhoff, G.-J., Zardini, A. A., Zhang, K., van Zyl, P. G., Kerminen, V.-M., S Carslaw, K., and Pandis, S. N.: General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales, Atmos. Chem. Phys., 11, 13061–13143, http://dx.doi.org/10.5194/acp-11-13061-2011doi:10.5194/acp-11-13061-2011, 2011. Laakso, L., Mäkelä, J. M., Pirjola, L., and Kulmala, M.: Model studies on ion-induced nucleation in the atmosphere, J. Geophys. Res., 107, 4427, http://dx.doi.org/10.1029/2002JD002140doi:10.1029/2002JD002140, 2002. 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, http://dx.doi.org/10.5194/acp-8-4823-2008doi:10.5194/acp-8-4823-2008, 2008. Lehtipalo, K., Sipilä, M., Junninen, H., Ehn, M., Brendt, T., Kajos, M. K., Worsnop, D. R., Petäjä, T., and Kulmala, M.: Observations of Nano-CN in the Nocturnal Boreal Forest, Aerosol Sci. Technol., 45, 499–509, 2011. Leppä, J., Anttila, T., Kerminen, V.-M., Kulmala, M., and Lehtinen, K. E. J.: Atmospheric new particle formation: real and apparent growth of neutral and charged particles, Atmos. Chem. Phys., 11, 4939–4955, http://dx.doi.org/10.5194/acp-11-4939-2011doi:10.5194/acp-11-4939-2011, 2011. Lohmann, U. and Feichter, J.: Global indirect aerosol effects: a review, Atmos. Chem. Phys., 5, 715–-737, http://dx.doi.org/10.5194/acp-5-715-2005doi:10.5194/acp-5-715-2005, 2005 Manninen, H. E., Nieminen, T., Asmi, E., Gagné, S., Häkkinen, S., Lehtipalo, K., Aalto, P., Vana, M., Mirme, A., Mirme, S., Hõrrak, U., Plass-Dülmer, C., Stange, G., Kiss, G., Hoffer, A., Tör\Ho, N., Moerman, M., Henzing, B., de Leeuw, G., Brinkenberg, M., Kouvarakis, G. N., Bougiatioti, A., Mihalopoulos, N., O'Dowd, C., Ceburnis, D., Arneth, A., Svenningsson, B., Swietlicki, E., Tarozzi, L., Decesari, S., Facchini, M. C., Birmili, W., Sonntag, A., Wiedensohler, A., Boulon, J., Sellegri, K., Laj, P., Gysel, M., Bukowiecki, N., Weingartner, E., Wehrle, G., Laaksonen, A., Hamed, A., Joutsensaari, J., Petäjä, T., Kerminen, V.-M., and Kulmala, M.: EUCAARI ion spectrometer measurements at 12 European sites – analysis of new particle formation events, Atmos. Chem. Phys., 10, 7907–7927, http://dx.doi.org/10.5194/acp-10-7907-2010doi:10.5194/acp-10-7907-2010, 2010. Mertes, S., Schröder, F., and Wiedensohler, A.: The particle detection efficiency curve of the TSI-3010 CPC as a function of temperature difference between saturator and condenser, Aerosol Sci. Technol., 23, 257–261, 1995. Millikan, R. A.: The general law of fall of a small spherical body through a gas, and its bearing upon the nature of molecular reflection from surfaces, Phys. Rev., 22, 1–23, 1923. Mikkonen, S., Romakkaniemi, S., Smith, J. N., Korhonen, H., Petäjä, T., Plass-Duelmer, C., Boy, M., McMurry, P. H., Lehtinen, K. E. J., Joutsensaari, J., Hamed, A., Mauldin III, R. L., Birmili, W., Spindler, G., Arnold, F., Kulmala, M., and Laaksonen, A.: A statistical proxy for sulphuric acid concentration, Atmos. Chem. Phys., 11, 11319–11334, http://dx.doi.org/10.5194/acp-11-11319-2011doi:10.5194/acp-11-11319-2011, 2011. Mirme, A., Tamm, E., Mordas, G., Vana, M., Uin, J., Mirme, S., Bernotas, T., Laakso, L., Hirsikko, A., and Kulmala, M.: A wide-range multi-channel Air Ion Spectrometer, Boreal Environ. Res., 12, 247–264, 2007. Myhre, G: Consistency between satellite-derived and modeled estimates of the direct aerosol effect, Science, 325, 187–190, 2009. Mönkkönen, P., Uma, R., Srinivasan, D., Koponen, I. K., Lehtinen, K. E. J., Hämeri, K., Suresh, R., Sharma, V. P., and Kulmala, M.: Relationship and variation of aerosol number and PM$_10$ mass concentrations in a highly polluted urban environment – New Delhi, India, Atmos. Environ., 38, 425–433, 2004. Mönkkönen, P., Koponen, I. K., Lehtinen, K. E. J., Hämeri, K., Uma, R., and Kulmala, M.: Measurements in a highly polluted Asian mega city: observations of aerosol number size distribution, modal parameters and nucleation events, Atmos. Chem. Phys., 5, 57–66, http://dx.doi.org/10.5194/acp-5-57-2005doi:10.5194/acp-5-57-2005, 2005. Paasonen, P., Nieminen, T., Asmi, E., Manninen, H. E., Petäjä, T., Plass-Dülmer, C., Flentje, H., Birmili, W., Wiedensohler, A., Hõrrak, U., Metzger, A., Hamed, A., Laaksonen, A., Facchini, M. C., Kerminen, V.-M., and Kulmala, M.: On the roles of sulphuric acid and low-volatility organic vapours in the initial steps of atmospheric new particle formation, Atmos. Chem. Phys., 10, 11223–11242, http://dx.doi.org/10.5194/acp-10-11223-2010doi:10.5194/acp-10-11223-2010, 2010. Petäjä, T., Mauldin, III, R. L., Kosciuch, E., McGrath, J., Nieminen, T., Paasonen, P., Boy, M., Adamov, A., Kotiaho, T., and Kulmala, M.: Sulfuric acid and OH concentrations in a boreal forest site, Atmos. Chem. Phys., 9, 7435–7448, http://dx.doi.org/10.5194/acp-9-7435-2009doi:10.5194/acp-9-7435-2009, 2009. Pope, C. A. and Dockery, D. W.: Health effects of fine particulate air pollution: lines that connect, J. Air Waste Manage., 56, 709–742, 2006. Quaas, J., Ming, Y., Menon, S., Takemura, T., Wang, M., Penner, J. E., Gettelman, A., Lohmann, U., Bellouin, N., Boucher, O., Sayer, A. M., Thomas, G. E., McComiskey, A., Feingold, G., Hoose, C., Kristjánsson, J. E., Liu, X., Balkanski, Y., Donner, L. J., Ginoux, P. A., Stier, P., Grandey, B., Feichter, J., Sednev, I., Bauer, S. E., Koch, D., Grainger, R. G., Kirkevåg, A., Iversen, T., Seland, Ø., Easter, R., Ghan, S. J., Rasch, P. J., Morrison, H., Lamarque, J.-F., Iacono, M. J., Kinne, S., and Schulz, M.: Aerosol indirect effects – general circulation model intercomparison and evaluation with satellite data, Atmos. Chem. Phys., 9, 8697–8717, http://dx.doi.org/10.5194/acp-9-8697-2009doi:10.5194/acp-9-8697-2009, 2009. Riipinen, I., Sihto, S.-L., Kulmala, M., Arnold, F., Dal Maso, M., Birmili, W., Saarnio, K., Teinilä, K., Kerminen, V.-M., Laaksonen, A., and Lehtinen, K. E. J.: Connections between atmospheric sulphuric acid and new particle formation during QUEST III-IV campaigns in Heidelberg and Hyytiälä, Atmos. Chem. Phys., 7, 1899–1914, http://dx.doi.org/10.5194/acp-7-1899-2007doi:10.5194/acp-7-1899-2007, 2007. Russell, A. G. and Brunekreef, B.: A focus on particulate matter and health, Environ. Sci. Technol., 43, 4620–4625, 2009. Ruuskanen, J., Tuch, T., Ten Brink, H., Peters, A., Khlystov, A., Mirme, A., Kos, G. P. A., Brunekreef, B., Wichmann, H. E., Buzorius, G., Vallius, M., Kreyling, W. G., and Pekkanen, J.: Concentrations of ultrafine, fine and PM$_2.5$ particles in three European cities, Atmos. Environ., 35, 3729–3738, 2001. Scott, G. M.: The Development of a Methodology for the Delineation of Air Quality Management Areas in South Africa, Ph.D. thesis, University of KwaZulu Natal, Durban, 2010. Sihto, S.-L., Kulmala, M., Kerminen, V.-M., Dal Maso, M., Petäjä, T., Riipinen, I., Korhonen, H., Arnold, F., Janson, R., Boy, M., Laaksonen, A., and Lehtinen, K. E. J.: Atmospheric sulphuric acid and aerosol formation: implications from atmospheric measurements for nucleation and early growth mechanisms, Atmos. Chem. Phys., 6, 4079–4091, http://dx.doi.org/10.5194/acp-6-4079-2006doi:10.5194/acp-6-4079-2006, 2006. Sipilä, M., Brendt, T., Petäjä, T., Brus, D., Vanhanen, J., Stratmann, F., Patokoski, J., Mauldin III, R. L., Hyvärinen, A.-P., Lihavainen, H., and Kulmala, M.: The role of sulphuric acid in atmospheric nucleation, Science, 32, 1243–1246, 2010. Stanier, C. O., Khlystov, A. Y., and Pandis, S. N.: Ambient aerosol size distributions and number concentrations measured during the Pittsburgh Air Quality Study (PAQS), Atmos. Environ., 38, 3275–3284, 2004. Suni, T., Kulmala, M., Hirsikko, A., Bergman, T., Laakso, L., Aalto, P. P., Leuning, R., Cleugh, H., Zegelin, S., Hughes, D., van Gorsel, E., Kitchen, M., Vana, M., Hõrrak, U., Mirme, S., Mirme, A., Sevanto, S., Twining, J., and Tadros, C.: Formation and characteristics of ions and charged aerosol particles in a native Australian Eucalypt forest, Atmos. Chem. Phys., 8, 129–139, http://dx.doi.org/10.5194/acp-8-129-2008doi:10.5194/acp-8-129-2008, 2008. Svenningsson, B., Arneth, A., Hayward, S., Holst, T., Massling, A., Swietlicki, E., Hirsikko, A., Junninen, H., Riipinen, I., Vana, M., Dal Maso, M., Hussein, T., and Kulmala, M.: Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland-forest mosaic, Tellus, 60B, 353–364, 2008. Tyson, P. D., Garstang, M., and Swap, R.: Large-scale re-circulation of air over southern Africa, J. Appl. Meteorol., 35, 2218–2236, 1996. Vakkari, V., Laakso, H., Kulmala, M., Laaksonen, A., Mabaso, D., Molefe, M., Kgabi, N., and Laakso, L.: New particle formation events in semi-clean South African savannah, Atmos. Chem. Phys., 11, 3333–3346, http://dx.doi.org/10.5194/acp-11-3333-2011doi:10.5194/acp-11-3333-2011, 2011. Venter, A. D., Vakkari, V., Beukes, J. P., van Zyl, P. G., Laakso, H., Mabaso, D., Tiitta, P., Josipovic, M., Kulmala, M., Pienaar, J. J., and Laakso, L.: An air quality assessment in the industrialized western Bushveld Igneous Complex, South Africa, S. Afr. J. Sci., accepted, 2012. Virkkula, A., Hirsikko, A., Vana, M., Aalto, P. P., Hillamo, R., and Kulmala, M.: Charged particle size distributions and analysis of particle formation events at the Finnish Antarctic research station Aboa, Boreal Environ. Res., 12, 397–408, 2007. Weber, R. J., Marti, J. J., McMurry, P. H., Eisele, F. L., Tanner, D. J., and Jefferson, A.: Measured atmospheric new particle formation rates: Implications for nucleation mechanisms, Chem. Eng. Commun, 151, 53–64, 1996. Wehner, B. and Wiedensohler, A.: Long term measurements of submicrometer urban aerosols: statistical analysis for correlations with meteorological conditions and trace gases, Atmos. Chem. Phys., 3, 867–879, http://dx.doi.org/10.5194/acp-3-867-2003doi:10.5194/acp-3-867-2003, 2003. Wenig, M., Spichtinger, N., Stohl, A., Held, G., Beirle, S., Wagner, T., Jähne, B., and Platt, U.: Intercontinental transport of nitrogen oxide pollution plumes, Atmos. Chem. Phys., 3, 387–393, http://dx.doi.org/10.5194/acp-3-387-2003doi:10.5194/acp-3-387-2003, 2003. Winklmayr, W., Reischl, G., Lindner, A., and Berner, A.: A new electromobility spectrometer for the measurement of aerosol size distributions in the size range from 1 to 1000 nm, J. Aerosol Sci., 22, 289–296, 1991. Woo, K. S., Chen, D. R., Pui, d. Y. H., and McMurry, P. H.: Measurement of Atlanta aerosol size distributions: observations of ultrafine particle events, Aerosol Sci. Technol., 34, 75–87, 2001. Wu, Z., Hu, M., Lin, P., Wehner, B., and Wiedensohler, A.: Particle number size distribution in the urban atmosphere of Beijing, China, Atmos. Environ., 42, 7967–7980, 2008. Wu, Z., Hu, M., Yue, D., Wehner, B., and Wiedensohler, A.: Evolution of particle number size distribution in an urban atmosphere during episodes of heavy pollution and new particle formation, Science China, Earth Sciences, 54, 1772–1778, 2011. Xiao, Z. and Laplante, A. R.: Characterizing and recovering the platinum group minerals – a review, Miner. Eng., 17, 961–979, 2004. Yli-Juuti, T., Riipinen, I., Aalto, P. P., Nieminen, T., Maenhaut, W., Janssens, I. A., Clayas, M., Salma, I., Ocskay, R., Hoffer, A., Imre, K., and Kulmala, M.: Characteristics of new particle formation events and cluster ions at K-Puszta, Hungary, Boreal Environ. Res., 14, 683–698, 2009. Yli-Juuti, T., Nieminen, T., Hirsikko, A., Aalto, P. P., Asmi, E., Hõrrak, U., Manninen, H. E., Patokoski, J., Dal Maso, M., Petäjä, T., Rinne, J., Kulmala, M., and Riipinen, I.: Growth rates of nucleation mode particles in Hyytiälä during 2003–2009: variation with particle size, season, data analysis method and ambient conditions, Atmos. Chem. Phys., 11, 12865–12886, http://dx.doi.org/10.5194/acp-11-12865-2011doi:10.5194/acp-11-12865-2011, 2011. Yu, F., Luo, G., Bates, T. S., Andersson, B., Clarke, A., Kapustin, V., Yantosca, R. M., Wang, Y., and Wu, S.: Spatial distributions of particle number concentrations in the global troposphere: Simulations, observations, and implications for nucleation mechanism, J. Geophys. Res., 115, D17205, http://dx.doi.org/10.1029/2009JD013473doi:10.1029/2009JD013473, 2010. Yue, D., Hu, M., Wu, Z., Wang, Z., Guo, S., Wehenr, B., Nowak, A., Achtert, P., Wiedensohler, A., Jung, J., Kim, Y. J., and Liu, S.: Characteristic of aerosol size distributions and new particle formation in the summer in Beijing, J. Geophys. Res., 114, D00G12, http://dx.doi.org/10.1029/2008JD010894doi:10.1029/2008JD010894, 2009.