Chemical speciation of size-segregated aerosol samples collected at an urban location in Central Argentina

LANZACO, BETHANIA L.; OLCESE, LUIS E.; TOSELLI, BEATRIZ M.; LÓPEZ, MARÍA LAURA

Campinas

Encuentro; 27 RAU Annual Users Meeting LNLS/CNPEM; 2017

Laboratorio Nacional de Luz Sincrotron

Aerosol sampling was conducted for the winter-spring months of years 2014-2015 at an urban site of Córdoba City. Córdoba is the second largest city of Argentina and an important industrial and touristic centre. 175 samples were collected in 6-h intervals and five size fractions, using a SIOUTAS impactor (SKC). The impactor is a miniaturized cascade impactor consisting of four impaction stages and one after-filter. Particles in the aerodynamic diameter ranges < 0.25, 0.25-0.5, 0.5-1.0, 1.0-2.5, and 2.5-10 microns were collected on Teflon filters. The Sioutas impactor operates at a flow rate of 9 L min?1. All the collected samples were later individually analyzed by SR-XRF at the Brazilian Synchrotron Light Source Laboratory (LNLS), in Campinas City. The measurements were carried out using the D09B-XRF beam line. Aerosol samples were excited with monochromatic beams of 10 keV and 13.5 keV to obtain size-segregated elemental aerosol mass concentrations for Mg, Al, Si, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb. The high sensitivity of SR-XRF allows for very low detection limits for most of the above elements [1]. It is recognized that the composition and size of particulate matter (PM) is largely determined by its source, making identification of them and its size-segregated components [2], critical to defining source-specific health risks. The results of the present study permitted to differentiate elements that are mainly emitted from mechanical processes from those that are emitted through the engine exhaust. The former have their origins in road resuspension (Al, Fe, Si, Ca, Ti) and are concentrated in the coarse size range (larger than 1 micron). The latter are mainly formed inside the engine and are concentrated in the finest fraction. However, there are some elements, such as Mn, Cr, Zn, Ni, and Cu, that by the size distribution, seems to have a double origin, i.e. in the interior of the engine and in mechanical wearing. The average elemental concentration measured in this work revealed that the most toxic metals (i.e. Cr, Zn, Ni, Cu, and Mn) tended to have an important contribution in the finest size fraction of the particulate matter. In the present study, fine and ultrafine source identification was carried out by inspection of key species in source profiles, comparison with literature data and the knowledge of the city. As an outcome of this work, the results of detailed source apportionment of the finer fractions measured in the city are presented together with an analysis of the meteorological condition and number concentrations of the particulate matter for the same size fractions.