Sources and distribution of tracer elements in road dust: The Venice mainland case of study

Abstract

Road dust is an important non-exhaust traffic source of atmospheric particulate matter, from re-suspension of finer particles carried out by wind and traffic flow. Particles of road dust have both natural and anthropogenic origin; the latter is characterized by higher concentrations of several pollutants and are significantly emitted by other non-exhaust traffic source such as the brake and road wear process. Therefore the discrimination between atmospheric particles directly emitted from abrasion process and those related to re-suspension is currently an open issue.Unlike the exhaust sources related to the fuel combustion, the non-exhaust emissions are not regulated by Communitarian Directives, although their percentage contribution is becoming more relevant due to the recent technological upgrades in the automotive field, focused on the reduction of exhaust emissions.In this work we studied the morphology and the chemical composition of road dust particles collected on urban, sub-urban and rural roads of Venice mainland (Northern Italy) in August 2013. Results of SEM-EDS and ICP-OES were processed with statistical tools (i.e., enrichment factors and principal components analysis) in order to identify the main pollutant sources affecting the monitored areas. Peculiar associations among Cr, Mn, Zn, Cu, Fe suggested brake pads and tires wear as the dominant source of these elements, whereas the presence of Pb, Co, Ba, Ti was attributed to the tear of the painted horizontal signals. Moreover, the presence of particles originated from the latter source was also confirmed by the presence of glass beads with diameters ranging from 20μm to 250μm.