Basic characteristics of atmospheric particles, trace gases and meteorology in a relatively clean Southern African Savannah environment

• Main Authors: L. Laakso, H. Laakso, P. P. Aalto, P. Keronen, T. Petäjä, T. Nieminen, T. Pohja, E. Siivola, M. Kulmala, N. Kgabi, M. Molefe, D. Mabaso, D. Phalatse, K. Pienaar, V.-M. Kerminen
• Format: Article
• Language: English
• Published: Copernicus Publications 2008-08-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/8/4823/2008/acp-8-4823-2008.pdf
• ISSN: 1680-7316; 1680-7324

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 SO<sub>2</sub>, 1.4 ppb for NO<sub>x</sub>, 36 ppb for O<sub>3</sub> and 105 ppb for CO. The corresponding PM<sub>1</sub>, PM<sub>2.5</sub> and PM<sub>10</sub> concentrations were 9.0, 10.5 and 18.8 μg m<sup>−3</sup>, and the annual median total particle number concentration in the size range 10–840 nm was 2340 cm<sup>−3</sup>. During Easterly winds, influence of industrial sources approximately 150 km away from the measurement site was clearly visible, especially in SO<sub>2</sub> and NO<sub>x</sub> concentrations. Of gases, NO<sub>x</sub> and CO had a clear annual, and SO<sub>2</sub>, NO<sub>x</sub> and O<sub>3</sub> 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<sup>−3</sup> s<sup>−1</sup> (median 1.9 cm<sup>−3</sup> s<sup>−1</sup>) and nucleation mode particle growth rates were in the range 3–21 nm h<sup>−1</sup> (median 8.5 nm h<sup>−1</sup>). 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.