Characteristics and composition of the falling dust sediments on Riyadh city, Saudi Arabia

Riyadh city, the capital of Saudi Arabia, receives annually a considerable amount of dust. Dust samples were collected on a monthly or bi-monthly basis, from eight different locations in Riyadh during the period from March 1991 to February 1992. They were analysed for particle size distribution as well as physio-chemical and mineralogical compositions. The dust fractions lie between loam and silt loam, having an average composition of 37% sand, 47% silt and 16% clay. CaCO3content, EC and pH were rather high and averaged 31•8%, 4•8 dSm−1and 8•9, respectively. Results showed that dust samples contained considerable levels of some trace elements. Mean values of the detected elements (in μg g−1were Pb, 66•8; Ni, 26•0; Co, 20•6; Cd, 3•8; Zn, 141•8. Mn, 318•9; and Cu, 36•4. In addition to natural sources, these higher values may be related to other traditional sources such as motor vehicle emissions. Mineralogical analysis indicated that the dominant minerals in the dust samples were quartz and calcite.