PM events and changes in the chemical composition of urban aerosols: A case study in the western Mediterranean.

More than 400 PM and 400 PM daily samples were collected in the urban center of Elche (close to the Spanish Mediterranean coast) from February 2015 to February 2018. Samples were analyzed to determine the concentrations of major and trace components with the aim of evaluating the influence of specific pollution events on the chemical composition of both PM fractions. The concentrations of crustal elements in PM significantly increased during Saharan dust outbreaks, particularly titanium, which has been identified as a good tracer of these events in the study area. Sulfate and nitrate levels were also enhanced due to secondary aerosol formation on mineral dust particles. Local pollution episodes had a great impact on submicron nitrate, whose mean concentration was more than four times higher than on non-event days. The chemical mass closure method was used to reconstruct PM and PM concentrations. Reasonably good correlations between measured and reconstructed concentrations were obtained, except for PM samples collected during Saharan dust events. This was due to the underestimation of the dust contribution during these episodes. Moderate differences in the average chemical composition of PM were observed between event and non-event days. Regarding PM, only local pollution episodes had a certain impact on its chemical composition.