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

Abstract

Compliance with air quality standards requires control of source emissions: fine exhaust particles are already subject to regulation but vehicle fleets increase whilst the non-exhaust emissions are totally uncontrolled. Emission inventories are scarce despite their suitability for researchers and regulating agencies for managing air quality and PM reduction measures. Only few countries in Europe proposed street cleaning as a possible control measure, but its effectiveness is still far to be determined. This study offers first estimates of Real-world Emission Factors for PM 10 and brake-wear elements and the effect on PM 10 concentrations induced by intense street cleaning trials. A straightforward campaign was carried out in the city of Barcelona with hourly elemental composition of fine and coarse PM to detect any short-term effect of street cleaning on specific tracers of non-exhaust emissions. Samples were analyzed by Particle Induced X-Ray Emission. Real-world Emission Factor for PM 10 averaged for the local fleet resulted to be 97 mg veh. When compared to other European studies, our EF resulted higher than what found in UK, Germany, Switzerland and Austria but lower than Scandinavian countries. For brake-related elements, total EFs were estimated, accounting for the sum of direct and resuspension emissions, in 7400, 486, 106 and 86 μg veh, respectively for Fe, Cu, Sn and Sb. In PM 2.5 Fe and Cu emission factors were respectively 4884 and 306 μg veh − 1 km − 1 .Intense street cleaning trials evidenced a PM 10 reduction at kerbside of 3 μg m − 3 (mean daily levels of 54 μg m − 3 ), with respect to reference stations. It is important to remark that such benefit could only be detected in small time-integration periods (12:00-18:00) since in daily values this benefit was not noticed. Hourly PM elemental monitoring allowed the identification of mineral and brake-related metallic particles as those responsible of the PM 10 reduction.

Emission factors from road dust resuspension in a Mediterranean freeway

“…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.…”

“…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. However, the metal emissions due to resuspension are still considerable and should be considered in Emission Inventories and Air Quality Plans.…”

Re-entrained road dust PM10 emission from selected streets of Krakow and its impact on air quality

“…PM10 dust in the air can be of the anthropogenic origins, but it can also result from physiochemical reactions between different substances present in the air (secondary organic and inorganic aerosols) [7]. Numerous studies on the PM10 chemical composition conducted for the areas within street canyons point out that the particulate matter does not solely originate from fuel combustion in motor vehicles, but constitutes a mixture of dusts of different origins and individual chemical compositions [8].…”

“…Particles with a diameter of 2.5-10 µm and more are emitted primarily from the road surfaces, where the dust originating from industry and energy sector is deposited together with the particulate matter resulting from abrasion of the road surface, car tires and brake pads as well as particles caused by the wind erosion processes and dust loading brought from construction sites, unpaved roads, etc. [7,[11][12][13]. Passing motor vehicles create a vacuum in the space between the road and car chassis, triggering the entrainment of the dust from the road to the air.…”

“…Research carried out in the US city of Tucson (Arizona) in the winter showed that the fraction of particulate matter from the fuel combustion in car engines and the share of re-entrained road dust ranged from 4-40 % and 30-50 % of the total PM10 concentration in the air, respectively [21]. On the other hand, the study conducted in Barcelona (Spain) [7] pointed out that the ratio of PM10 emissions from automotive engines to PM10 resuspended dust emissions from roads is equal to only 1.2. However, the same emission ratio for PM2.5 particulate matter is equal to 4.…”