Abstract: Air pollution in cities plays an important deleterious impact on morbidity and mortality of their population. Among the most targeted pollutants, particulate matter with aerodynamic diameter below 10 μm (PM10) has been widely related to serious health outcomes, including cardiorespiratory diseases, reduced life expectancy and premature mortality. Traffic-related emissions are often pointed out as the main source of PM and responsible for most of the exceedances of PM10 registered in European cities. Over the last decades, technological advances, such as catalytic converters and particulate filters, have contributed to significant reductions of tailpipe emissions. However, main cities in Europe have not experienced the expected drop in PM10 concentrations, a fact that is attributed to non-exhaust emissions (NEE). NEE comprise tyre wear, brake wear and road dust ressuspension. These emissions can significantly contribute to exposure to carbonaceous compounds, heavy metals, metalloids and mineral matter. Emissions from the resuspension of road dust depend on the vehicle fleet, meteorological conditions, type of pavement and surrounding conditions. In Portugal the main efforts to characterise these emissions have been focused on large and coastal cities. The lack of emission factors and chemical profiles can compromise the application of emission inventories, air quality models and the accurate assessment of health risks. With the aim of characterising the PM10 fraction, a mobile resuspension chamber with a gravimetric sampler (Echo Tecora, Italy) was used to collect road dust from eleven roads in Bragança, northwestern of Portugal. Monitoring was conducted only on sunny days and dry roads. At each sampling site, at least 3 replicates samples were collected, each one covering an area of 2 m x 3 m on the right side of one of the lanes, where most processes of abrasion and tyre-road interactions happen. The sampling locations comprised urban (7 points) and periurban (4 points) areas. The PM10 samples were analysed for organic and elemental carbon (OC and EC) by a thermo-optical technique and elemental composition by ICP-MS and ICP-OES. Dust loadings of 0.34 ± 0.28 mg PM10 m-2 were obtained for urban roads. A higher mean value was achieved inside the tunnel in the city centre (1.03 mg PM10 m-2 ). The emission factors ranged from 2.16 to 10.2 mg km-1 veh-1 and from 3.25 to 6.53 mg km-1 veh-1 for the periurban and urban areas, respectively. Irrespective of the sample, high enrichment factors (EF) were estimated for Cu and Zn. In addition, other traffic- related elements, such as P, S, Cr, Sn and Pb, also presented significant enrichements (EF >10). Moreover, a periurban road without strong influence of traffic exhibited extremely high enrichements for Co (50), S (406) and P (698), suggesting the use of pesticides on surrounding areas. Total carbon (TC) represented a PM10 mass fraction of 8-30%, while metal oxides accounted for 8-73%. The most abundant elements in their oxidesed form were Ca (7%), Al (6.5%), Fe (5%), Mg (3.6%) and S (2.45%). Other PM10-bound elements accounted, in total, for up to 1% of the PM10 mass. In general, the results showed a spatial variability of PM10-bound metals. The results obtained for Bragança denote low concentrations of PM10-bound elements when compared with other studies carried out in Portugal, such as Porto, Aveiro, and Lisbon.

Keywords: PM10; Road Dust Ressuspension; Emission Factors; Elements; Enrichment Factor; Chemical Profiles.