Overview
Excessive load of the ambient air with fine particles (PM10) is one of the most pressing issues of air pollution control. The limit values are exceeded not only in urban environments but also along national highways. The current debates in the context of the widespread exceedances of the EU limit values show strong public concern in this problem.
Particle emissions of road traffic are generally associated with exhaust emissions. Until recently particle emissions due to abrasion processes were neglected. However, the research project ASTRA2000/415 showed clearly the important contribution of these emissions to the PM10 load of the ambient air. They consist of particles from the abrasion of pavings, tyres, breaks and clutches. But no quantitative information is available about the contributions of the single processes. This, however, would be necessary for effective PM10 reduction scenarios. In particular it is important to know whether abrasion emissions from pavings or from vehicles are dominating.
The main scope of the project APART (Abrasion PArticles produced by Road Traffic) was to identify and quantify the non-exhaust fraction of traffic related PM10 for several road-side locations with characteristic traffic regimes.
Specific goals:
- To provide a reliable base for future PM10 reduction scenarios
- To determinate location-specific emission factors (mg/km/vehicle) for trace elements emitted by local road traffic.
- To calculate location-specific emission factors (mg/km/vehicle) for individual non-exhaust emission sources.
- To separate emission factor values for light duty vehicles (LDV) and heavy duty vehicles (HDV).
- To evaluate the local mass contribution from individual non-exhaust sources (% of traffic related PM10).
The scope of the project:
- The study focused on traffic related emissions and did not include a quantification of other PM10 sources.
- Exhaust related PM10 was quantified at the investigated locations to establish a mass balance of total traffic related PM10. An in-depth interpretation of the exhaust fraction is however subject of other studies and was not within the scope of the present investigation.
The research plan is based on particle measurements upwind and downwind of roads similarly to the already realised project ASTRA2000/415. What is new is the use of rotating-drum-impactors and of the new synchrotron x-ray facility at PSI which allows analysis of the elemental composition with high time resolution. This is a prerequisite for the identification and quantification of the single abrasion processes. BUWAL is interested in the project and would support it.
Funding
Results
The following statements were formulated based on the performed investigations and provide indications for future pollution abatement strategies:
- Mass contribution of non-exhaust sources: During the time periods considered for the measurements in the street canyon at Zürich-Weststrasse (February and March 2007) and along the national freeway A2 in Reiden LU (October and November 2007), the sum of direct abrasion sources and vehicle induced road dust resuspension made up 60% of the total traffic related PM10 emissions.
- Brake wear: Brake wear was characterised by a characteristic pattern of Fe, Cu, Zn, Mo, Zr, Sn, Sb and Ba, which is similar to real-world fleet emissions for brake wear reported in other studies. In contrast, the pattern of these elements in individual brake linings is extremely inhomogeneous. Compared to older studies, the measured emission factors for brake wear related lead (Pb) were considerably lower, indicating that lead has in the mean time largely been replaced in brake linings. At Zürich-Weststrasse, the heavily disturbed traffic flow resulted in brake wear emissions that made up 20% (15 mg/km/vehicle) of the total PM10 emissions from traffic. In contrast, brake wear emissions contributed less along the freeway in Reiden (3%, 3 mg/km/vehicle), due to the freeflowing traffic regime. For both locations the brake wear emissions from heavy duty vehicles were approximately 10 times higher than from light duty vehicles.
- Traffic induced resuspension of road dust: Generally, road dust resuspension is strongly influenced by available road dust and thus by the pollution of the road surface. In the street canyon at Zürich-Weststrasse, up to 40% of the traffic related PM10 emissions were assigned to resuspended road dust during the period of measurements in February and March 2007. Along the freeway in Reiden, the contribution of resuspended road dust to traffic related PM10 emissions was estimated to be higher than 50% in October and November 2007. In the heavily trafficked street canyon at Zürich-Weststrasse, the available dust on the surface was resuspended and kept in suspended state mainly by the turbulence induced by the heavy duty vehicles, leaving only small amounts of dust to be resuspended by the light duty vehicles.
- Road wear and tire wear: PM10 contributions from road wear and tire wear were not directly identified from the measurements at Zürich-Weststrasse and Reiden. Controlled experiments with a mobile load sim
Innovation aspects
Identification and quantification of the non-exhaust fraction of traffic related PM10 for several road-side locations with characteristic traffic regimes.
Policy implications
Environmental policy