Impact of Traffic Flows and Meteorological Events on the Hourly Elemental Composition of Fine and Coarse Particles at an Urban Site

Abstract

Hourly PM_2.5 and PM_2.5-10 samples were collected with a Streaker sampler over one week at an urban site located on the Spanish Mediterranean coast. The samples were subsequently analysed using the PIXE technique to determine their elemental composition. Despite the influence of traffic at the site, the atmospheric concentrations of the traffic-related components fell within the lower range of values reported for urban stations with similar characteristics. The concentrations of the elemental tracers for non-exhaust emissions (Cu, Zn, Mn, Al, Ca and Fe) in the PM_2.5-10 fraction displayed the strongest correlations with the traffic density (R² > 0.5), with lower correlation coefficients calculated for the fine fraction. A short Saharan dust episode identified during the study period increased the concentrations of the crustal elements (Al, Ca, K, Ti, Sr and Fe), mainly in the coarse fraction. Nevertheless, the concentrations of the sea-spray elements exhibited higher relative increases, indicating that the Saharan dust plume reached the sampling site following a marine path. The high temporal resolution of the PM sampling allowed us to identify the effects of a brief but intense precipitation event, during which a higher atmospheric removal efficiency, peaking at the rate of 17 L m^–2 in one hour, was observed for coarse particles than fine particles. As a result of this precipitation, most of the measured elemental concentrations in the PM_2.5-10 fraction decreased below detection limits.