7. Harmattan dust deposited in Ghana within 2000–2005

Abstract

Between 2000–2005, a monitoring system for the collection of harmattan dust over Ghana was established. Three methods were used to sample the harmattan dust: i) bowls with water, ii) plastic mats and iii) plates made of plywood. This paper describes the establishment of the monitoring system, and the regional distribution of harmattan dust trapped in various agro-ecological zones by the bowls with water and the mats. The bowl values represent the total amount of dust falling over a unit area, and the mat values represents the amount of dust retained by vegetation. The amount of harmattan dust captured is largest in the north where the mats retained about 20 g/cm³ compared to 5 g/cm³ in the south. The amount of dust retained differs significantly from year to year, and the particle-size of the dust becomes finer towards the south and with an increasing amount of organic matter. In the north, the median diameter was slightly above 15 mm and the organic carbon content was about 5% while in the south the median diameter was slightly above 5 µm and the organic carbon content was between 10 and 15%.