Thirty-two chemical species were determined in PM10 sampled at a suburban site on the north coast of Spain. Enrichment factors were applied to infer their soil/non-soil origin. The geochemical ratios were calculated using two databases: soil composition from locations in the surroundings of the sampling station and the Earth's average upper-crust composition. In the present study, dissimilarities were found between the enrichment factors obtained using these two databases. Al, Ti, La and Ce were taken as the reference elements to normalise the data, reaching analogous conclusions. Bi, Cd, Cu, Sb, Se, Sn and Zn were associated with predominantly non-soil apportionments. As the relevance of soil/non-soil sources for the other analysed elements was found to be variable, they were probably of mixed origin. Furthermore, pairs of elements showed strong relationships, thus pointing to a common origin. Na-Mg and Co-Ni, with Pearson correlation coefficients above 0.9, were respectively related to marine and industrial apportionments. Enrichment factors have proved to be a useful tool to distinguish the soil/non-soil origin of chemical species present in airborne particulate matter. However, the choice of the reference database for soil composition considerably determined the accuracy of the conclusions.
Keywords: Air quality; Crustal origin; Enrichment factor; Geochemistry; Particulate matter; Soil dust; UCC.