Real-World Emission Factors for Antimony and Other Brake Wear Related Trace Elements: Size-Segregated Values for Light and Heavy Duty Vehicles

Abstract

Hourly trace element measurements were performed in an urban street canyon and next to an interurban freeway in Switzerland during more than one month each, deploying a rotating drum impactor (RDI) and subsequent sample analysis by synchrotron radiation X-ray fluorescence spectrometry (SR-XRF). Antimony and other brake wear associated elements were detected in three particle size ranges (2.5-10, 1-2.5, and 0.1-1 microm). The hourly measurements revealed that the effect of resuspended road dust has to be taken into account for the calculation of vehicle emission factors. Individual values for light and heavy duty vehicles were obtained for stop-and-go traffic in the urban street canyon. Mass based brake wear emissions were predominantly found in the coarse particle fraction. For antimony, determined emission factors were 11 +/- 7 and 86 +/- 42 microg km(-1) vehicle(-1) for light and heavy duty vehicles, respectively. Antimony emissions along the interurban freeway with free-flowing traffic were significantly lower. Relative patterns for brake wear related elements were very similar for both considered locations. Beside vehicle type specific brake wear emissions, road dust resuspension was found to be a dominant contributor of antimony in the street canyon.

Emission factors from road dust resuspension in a Mediterranean freeway

“…As already mentioned, these studies estimated the total emission factors, accounting for direct emissions of brake-tire wear to the atmosphere plus the resuspension, whilst we estimated only the resuspension part. A similar finding was obtained by Bukowiecki et al (2009) who estimated that road dust resuspension was responsible only for a fifth part of the total non-exhaust emissions of Cu in the city center of Zurich. Our comparison with the city center study in Barcelona (Amato et al, 2010) qualitatively shows that most of the brake-related emissions come from direct emissions, rather than due to resuspension.…”

“…The EFs estimated in this study (0.029-0.031 mgCu VICT -1 ) are much smaller than those found in the city center of Barcelona (0.48 mgCu VKT" 1 , Amato et al, 2010), Oporto (0.26-0.40 mgCu VKT" 1 , Oliveira et al, 2010) or Zurich (0.50 mgCu VKT" 1 , Bukowiecki et al, 2009). As already mentioned, these studies estimated the total emission factors, accounting for direct emissions of brake-tire wear to the atmosphere plus the resuspension, whilst we estimated only the resuspension part.…”

“…In addition, the differences noted for EF PM between motorway and urban roads are hampered in the case of brake-related metals, due to the less frequency of braking. Bukowiecki et al (2009) found that EF (direct emission + resuspension) of brake-related metals from roadway were smaller than city center conditions by one order of magnitude. Finally, also the unaccounted fraction of soluble materials in our study must be kept in mind (e.g.…”

A comprehensive assessment of PM emissions from paved roads: Real-world Emission Factors and intense street cleaning trials

“…The C constant was in these cases relatively (in %) more significant, confirming that the fraction of ΔPM due to non traffic sources and non local traffic emissions was in the order of ng m . These values, similar to what obtained in previous studies (see Bukowiecki et al, 2009 as example) as well as those for r 2 , were robust enough to make reliable the EFs calculation. For Fe and Cu the fitted EF were respectively 7400 μg veh − 1 km − 1 and 486 μg veh…”

“…Similarly to previous studies (Bukowiecki et al, 2009;Johansson et al, 2009) we used Eq. (3) basing on the assumption that the dilution of the vehicle related emissions from the point of emission to the sampler inlets was comparable for NOx and the particulate pollutants.…”