Temporal and spatial variation of the chemical composition of PM10 at urban and rural sites in the Basel area, Switzerland

Particulate matter measurements of different size fractions (PM4, PM10, TSP) were performed in the Basel area (Switzerland) at seven urban sites throughout 1997 and at two urban and two rural sites during the following year (April 1998–May 1999). Based on a sample of filters which was chemically analyzed, we investigated the chemical composition of PM10 both within the city of Basel and among urban and rural sites. The temporal and spatial variability of the chemical composition of PM10 was evaluated taking into account additional data from meteorology and further air pollutants. The chemical analyses of PM10 showed that carbonaceous substances (elemental carbon, organic matter) and inorganic substances of secondary origin such as sulfate, nitrate and ammonium were the most abundant component of PM10 in the Basel area (approximately 60–70%). Difference in the PM10 concentration between urban and rural sites was larger during the cold season than during the warm season. This was mainly due to the presence of an inversion layer between the city and the more elevated rural sites resulting in higher concentrations of nitrate, ammonium and organic matter in the city during the cold season. The higher PM10 concentration on workdays compared to weekends was mostly a result of the temporal variation of the concentration of Ca, elemental carbon, Ti, Mn, and Fe, indicating that these compounds are for the most part caused by regional human activities. Although total PM10 mass concentration was found to be in general uniformly distributed within the city of Basel, the chemical composition was more variable due to specific sources like road traffic and other anthropogenic emissions.