Ambient measurements of selected VOCs in populated and remote sites of the Sahara desert

For the first time, ambient levels of benzene, toluene, carbon tetrachloride and selected oxygenated organic compounds have been measured in both populated and remote sites in the Sahara desert. The levels of these species were generally found to be high in the industrialized regions of the North Sahara, progressively decreasing with latitude so that lowest levels were reached in remote desert sites close to the Equator. The emissions from traffic, and the oil production and its transformation, together with the solvent use were the main anthropogenic sources determining the levels of aromatic, aliphatic and chlorinated organic compounds in desert sites near two Algerian cities. Substantial levels of acetone and some semi-volatile compounds, emitted or formed by photochemical reactions, were also found. Although some of these compounds were below the detection limits in the most remote sites of the Sahara desert located in Mauritania and Niger, measurable levels of benzene and toluene were still found together with significant amounts of acetone. Data seem to indicate that forest fires occurring in the tropical regions of the North African continent were the most likely sources for the background levels measured during most of our measurements. The data presented here did not differ too much from those measured in the most isolated sites of the northern hemisphere.