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

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 2 , 1.4 ppb for NO x , 36 ppb for O 3 and 105 ppb for CO. The corresponding PM 1 , PM 2.5 and PM 10 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 SO 2 and NO x concentrations. Of gases, NO x and CO had a clear annual, and SO 2 , NO x and O 3 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.

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