Site description

The Welgegund measurement site is positioned approximately 25 km north-west of Potchefstroom, Republic of South Africa (26°34'10"S, 26°56'21"E, 1480 m.asl). The annual average temperature in the area is around 18 degrees, with typical maximum summer temperatures around 30ºC and minimum winter temperatures around 0ºC. The precipitation over the area falls during the wet season starting in October and lasting until April. The dry winter season with almost no precipitation is from mid-May until mid-September.

Welgegund measurement station during the dry winter season.

The area surrounding the measurement station (a video clip taken 12/2012 from the roof) is grassland savannah grazed by cattle and sheep. The dominant vegetation comprises grasses, with geophytes and herbs also being well represented. The dominant grass species are Hyparrhenia hirta and Sporobolus pyramidalis. Non-grassy forbs include Acacia sieberiana, Rhus rehmanniana, Walafrida densiflora, Spermacoce natalensis, Kohautia cynanchica, and Phyllanthus glaucophyllus. The soil consists of sandy tilt.

The measurement site is located on a grazing field of a farm at the western edge of the main agricultural area of South Africa.

There are very few local pollution sources close to the site, but it is frequently hit by pollution plumes from Johannesburg greater metropolitan area. These plumes are often balanced with clean air injections from the western sector.

SO₂ emissions in southern Africa. The measurement site is indicated with magenta star. The areas with highest anthropogenic emissions in the whole are located approximately 100-300 km east of Welgegund.

Origin of air masses at Welgegund (based on hourly trajectories 2007-2008). Main pollution source areas and capitals are indicated with black dots.