Abstract
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.
Highlights
Air quality and interactions between land ecosystems and atmosphere in a changing climate are issues that influence most of the developing world
We have introduced a new atmospheric measurement site in Southern African savannah and presented the main results from a full year of aerosol and trace gas measurements
The site provides an optimal location between polluted industrial regions to the East and clean, sparsely-populated regions to the West of the measurement site
Summary
Air quality and interactions between land ecosystems and atmosphere in a changing climate are issues that influence most of the developing world. In Africa, for example, changing climate affect vegetation and may thereby cause emigration (Boko et al, 2007). Emigration, on the other hand, increase urban population and air pollution. Most of the population accumulates into urban areas, air quality is affected by the surrounding landscape. One spectacular example of this are the intensive dust episodes related to the Kosa desert in Asia, increasing occasionally PM10 concentrations up to values of about 1000 μg m−3 (Mori et al, 2002). For that reason, studying the air quality and anthropogenic influences in urban areas requires knowledge about the natural conditions, and in contrast, urban and industrial plumes may have an adverse effect on vegetation even far a way from the source of emissions. Vast areas of even sparse vegetation may contribute significantly to the global atmospheric chemistry (Guenther et al, 1996) and, via the formation of new aerosol particles, to the properties of clouds and global radiation balance (Went, 1960; Kurten et al, 2003; Kerminen et al, 2005)
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