『Abstract
　Soil and sand fine particles, which may be resuspended as fine dust in the atmosphere, contain a variety of anthropogenic and natural organic components. Samples of fine soil and sand particles (sieved to ＜125μM) were collected from the Riyadh area in the summer of 2003 and extracted with a mixture of dichloromethane and methanol (3:1, v:v(. The derivatized total extracts were analyzed by gas chromatography-mass spectrometry in order to characterize the composition and sources of the organic components. Both anthropogenic and natural biogenic inputs were the major sources of the organic compounds in these extracts. Discarded plastics and vehicular emission products were the major anthropogenic sources in the fine particles from populated areas of the city. their tracers were plasticizers, UCM, n-alkanes, hopanes and tracers of steranes. Vegetation was the major natural source of organic compounds in samples from outside Riyadh and included n-alkanols, n-alkanoic acids, n-alkanes, methyl alkanoates, sterols and triterpenoids. Carbohydrates had high concentrations (42-54％) in all samples and indicate sources from decomposition of cellulose and/or the presence of viable microbiota such as bacteria and fungi. The results were also compared with the data obtained in winter 2002 and showed that anthropogenic inputs were higher in summer than in winter, whereas the opposite trend was observed for natural inputs.

Keywords: Biomarkers; Carbohydrates; Lipids; Petroleum residues; Plasticizers; UCM』

Introduction
Experimental methods
　Sampling and extraction procedure
　Instrumental analysis
Results and discussion
　Anthropogenic sources
　Natural biogenic sources
　Anthropogenic versus natural sources
Conclusions
Acknowledgments
References