The Policy Relevance of Wear Emissions from Road Transport, Now and in the Future—An International Workshop Report and Consensus Statement

Abstract

Road transport emissions are a major contributor to ambient particulate matter concentrations and have been associated with adverse health effects. Therefore, these emissions are targeted through increasingly stringent European emission standards. These policies succeed in reducing exhaust emissions, but do not address "nonexhaust" emissions from brake wear, tire wear, road wear, and suspension in air of road dust.Is this a problem? To what extent do nonexhaust emissions contribute to ambient concentrations of PM 10 or PM 2.5 ? In the near future, wear emissions may dominate the remaining traffic-related PM 10 emissions in Europe, mostly due to the steep decrease in PM exhaust emissions. This underlines the need to determine the relevance of the wear emissions as a contribution to the existing ambient PM concentrations, and the need to assess the health risks related to wear particles, which has not yet received much attention. During a workshop in 2011, available knowledge was reported and evaluated so as to draw conclusions on the relevance of traffic-related wear emissions for air quality policy development. On the basis of available evidence, which is briefly presented in this paper, it was concluded that nonexhaust emissions and in particular suspension in air of road dust are major contributors to exceedances at street locations of the PM 10 air quality standards in various European cities. Furthermore, wear-related PM emissions that contain high concentrations of metals may (despite their limited contribution to the mass of nonexhaust emissions) cause significant health risks for the population, especially those living near intensely trafficked locations. To quantify the existing health risks, targeted research is required on wear emissions, their dispersion in urban areas, population exposure, and its effects on health. Such information will be crucial for environmental policymakers as an input for discussions on the need to develop control strategies.Implications: Road transport particulate matter (PM) emissions are associated with adverse health effects. Stringent policies succeed in reducing the exhaust PM emissions, but do not address "nonexhaust" emissions from brake wear, tire wear, road wear, and suspension in air of road dust. In the near future the nonexhaust emissions will dominate the road transport PM emissions. Based on the limited available evidence, it is argued that dedicated research is required on nonexhaust emissions and dispersion to urban areas from both an air quality and a public health perspective. The implicated message to regulators and policy makers is that road transport emissions continue to be an issue for health and air quality, despite the encouraging rapid decrease of tailpipe exhaust emissions.

Modelling street level PM<sub>10</sub> concentrations across Europe: source apportionment and possible futures

“…Additional local measures targeting road traffic may be required to ensure safe attainment of the limit values, which may include the reduction of traffic volumes through local traffic management such as low emission zones or incentives for public transport use, the reduction of road dust abrasion through restrictions on studded tyre use in Scandinavian countries (Kupiainen and Pirjola, 2011), use of enhanced road surface material or advanced road cleaning/dust binding practices (Amato et al, 2010;Denier et al, 2013).…”

Particulate Matter from the Road Surface Abrasion as a Problem of Non-Exhaust Emission Control

“…Nevertheless, we still lack detailed information [75,[80][81][82][83]. Data and rationales are missing for the reliable subdivision of PM emissions into those from exhaust vs. those from non-exhaust sources, for the separation of road-traffic related PM from PM related to other sources [20,62], and, above all, for the segmentation of PM generally derived from non-exhaust sources into specific source groups (tire abrasion, brakes, road surface, etc.…”

“…The physical removal of elements from road and street surfaces via washing and sweeping does not sufficiently limit human exposure to PM resulting from traffic emission [55]. The complex process of overlapping the so-called urban background onto road traffic pollutants, along with the associated physical changes and chemical reactions, lead to the conclusion that PM close to roads may be much more toxic or may have a higher carcinogenic potential than PM outside such areas [11,12,20,70,[74][75][76][77].…”

Coarse-Particle Passive-Sampler Measurements and Single-Particle Analysis by Transmitted Light Microscopy at Highly Frequented Motorways

“…Emission-control regulation led to a substantial reduction in exhaust emissions from road traffic in many cities and regions (Allen et al, 2006;Thorpe and Harrison, 2008;Mathissen et al, 2011). In contrast, the non-exhaust emissions from road vehicles are predicted to become more important (Kuhlbusch et al, 2009;Rexeis and Hausberger, 2009;Harrison et al, 2011;Amato et al, 2012;Harrison et al, 2012;Denier van der Gon et al, 2013) because an increase in the number of passenger cars (Light-duty vehicles, LDV), light commercial vehicles (LCV) and trucks (Heavy-duty vehicles, HDV) is expected (Rommerskirchen et al, 2012;ICCT, 2016).…”

“…Policy makers succeeded in reducing exhaust emissions, but did not and still do not address "non-exhaust" traffic emissions from brake wear, tire wear, road wear, and suspension in air of road dust. Road-transport emissions, which are associated with adverse health effects, will become an even more important PM source in the future, especially in urban and congested areas (Denier van der Gon et al, 2013).…”