INORGANIC WATER-SOLUBLE IONS IN ATMOSPHERIC PARTICLES OVER MARACAIBO LAKE BASIN IN THE WESTERN REGION OF VENEZUELA

The concentration of nine water soluble ions in aerosol samples on cel lulose filters collected by a high-volume cascade impactor was determi ned for two rural sites in Venezuela. Total suspended particles show a similar size distribution both dry and rainy seasons (MMDs similar to 2.5 mu m). The inorganic water soluble ions are similar to 30% by mas s of the TSP, from which, SO4-Cl-NH4 represent similar to 80%, and sul phate accounts for similar to 50%. An important enrichment respect to marine aerosols (>> 40%) was observed in the sequence: Cl- < Mg2+ < SO 42- < Ca2+ < K+. The substantially high non-sea-salt Cl- contrast with the considerable deficit of Cl- found in other savannah regions of Ve nezuela where this ion has a mainly marine origin. Several ions have s imilar mass median diameter: SO42- and NH4+ (MMDs similar to 0.7 mu m) ; Na+, Cl- and Mg2+ (MMDs similar to 3.6 mu m); K+ and NO3- (MMDs simi lar to 2.5 mu m), which held for both dry and rainy seasons. NH4+ and SO42- species are confined to the fine fraction < 1.5 mu m, which repr esent similar to 85% of the total atmospheric concentration, and the l arger amount of them is associated with particles < 0.49 mu m. Water s oluble particles have higher concentrations of inorganic ions than tho se observed in other regions of Venezuelan savannah, where important v egetation burning occurs during the year. Substantially higher differe nces are observed in SO42-, Ca2+, NH4+ and Cl- which can be up to 28; 7; 7 and 5 times higher, respectively. In general, the results indicat e that in Maracaibo Lake Basin, large agricultural and natural vegetat ion areas are probably affected by up wind anthropogenic sources as Oi l and Petrochemical industry and the city of Maracaibo with medium siz e industries; and that in this region, the atmosphere is not significa ntly polluted by emissions from burnt vegetation. (C) 1998 Elsevier Sc ience B.V.