Characterizations of Deposited Dust Fallout in Riyadh City, Saudi Arabia

Dust and sand storms are a persistent problem in the Kingdom of Saudi Arabia. We monitored dust fallout samples from 15 sampling sites on a monthly basis for the entire year of 2012 and analyzed them for the various chemical and physical characteristics. Results revealed that dust deposition rates across the city were high, with sites located near construction activities and those located in northeastern Riyadh being the worst. The annual average amount of dust fallout for all stations during this period was 454.1 tons km(-2). Compared to other cities, the total annual dust deposition observed in Riyadh was among the highest in the world. The average monthly amounts of dust deposited at 15 sites across Riyadh were highly variable, ranging from 14.5 tons km(-2) at Riyadh airport to 178.6 tons km(-2) at the Al-Aqiq site. Dust deposition rates varied significantly in April to August and ranged from 74.6 to 54.9 tons km(-2) month(-1). The dry deposition during November to December 2012 was significantly lower, with an average of 30.1 tons km(-2) month(-1). Silt fraction was the dominant fraction in almost all of the dust fallout and it ranged from 49.5% in Al-Aqiq to 70% in Al-Olya. The sand fraction ranged from 48.4% at Al-Aqiq to 26.2% at Al-Olya. All of the dust samples had a high CaCO3 content, ranging from 16.9 to 48.5%. Appreciable amounts of heavy metals such as Pb, Ni, Co, Cu, Mn, Zn, and V were detected in the dust samples.