Inorganic water soluble ions in atmospheric particles over Maracaibo Lake Basin in the western region of Venezuela

Abstract

The concentration of nine water soluble ions in aerosol samples on cellulose filters collected by a high-volume cascade impactor was determined for two rural sites in Venezuela. Total suspended particles show a similar size distribution both dry and rainy seasons (MMDs∼2.5 μm). The inorganic water soluble ions are ∼30% by mass of the TSP, from which, S0 4–Cl–NH 4 represent ∼80%, and sulphate accounts for ∼50%. An important enrichment respect to marine aerosols (≫40%) was observed in the sequence: Cl −<Mg 2+<SO 4 2−<Ca 2+<K +. The substantially high non-sea-salt Cl − contrast with the considerable deficit of Cl − found in other savannah regions of Venezuela where this ion has a mainly marine origin. Several ions have similar mass median diameter: SO 4 2− and NH 4 + (MMDs∼0.7 μm); Na +, Cl − and Mg 2+ (MMDs∼3.6 μm); K + and NO 3 − (MMDs∼2.5 μm), which held for both dry and rainy seasons. NH 4 + and SO 4 2− species are confined to the fine fraction <1.5 μm, which represent ∼85% of the total atmospheric concentration, and the larger amount of them is associated with particles <0.49 μm. Water soluble particles have higher concentrations of inorganic ions than those observed in other regions of Venezuelan savannah, where important vegetation burning occurs during the year. Substantially higher differences are observed in SO 4 2−, Ca 2+, NH 4 + and Cl − which can be up to 28; 7; 7 and 5 times higher, respectively. In general, the results indicate that in Maracaibo Lake Basin, large agricultural and natural vegetation areas are probably affected by up wind anthropogenic sources as Oil and Petrochemical industry and the city of Maracaibo with medium size industries; and that in this region, the atmosphere is not significantly polluted by emissions from burnt vegetation.