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Brake wear particle emissions: a review.

Grigoratos T, Martini G - Environ Sci Pollut Res Int (2014)

Bottom Line: Among non-exhaust sources, brake wear can be a significant particulate matter (PM) contributor, particularly within areas with high traffic density and braking frequency.As exhaust emissions control become stricter, relative contributions of non-exhaust sources-and therefore brake wear-to traffic-related emissions will become more significant and will raise discussions on possible regulatory needs.The aim of the present literature review study is to present the state-of-the-art of the different aspects regarding PM resulting from brake wear and provide all the necessary information in terms of importance, physicochemical characteristics, emission factors and possible health effects.

View Article: PubMed Central - PubMed

Affiliation: European Commission, Joint Research Centre, Sustainable Transport Unit (STU), Institute for Energy and Transport (IET), Via E Fermi 2749, 21027, Ispra, Italy, theodoros.grigoratos@jrc.ec.europa.eu.

ABSTRACT
Traffic-related sources have been recognized as a significant contributor of particulate matter particularly within major cities. Exhaust and non-exhaust traffic-related sources are estimated to contribute almost equally to traffic-related PM10 emissions. Non-exhaust particles can be generated either from non-exhaust sources such as brake, tyre, clutch and road surface wear or already exist in the form of deposited material at the roadside and become resuspended due to traffic-induced turbulence. Among non-exhaust sources, brake wear can be a significant particulate matter (PM) contributor, particularly within areas with high traffic density and braking frequency. Studies mention that in urban environments, brake wear can contribute up to 55 % by mass to total non-exhaust traffic-related PM10 emissions and up to 21 % by mass to total traffic-related PM10 emissions, while in freeways, this contribution is lower due to lower braking frequency. As exhaust emissions control become stricter, relative contributions of non-exhaust sources-and therefore brake wear-to traffic-related emissions will become more significant and will raise discussions on possible regulatory needs. The aim of the present literature review study is to present the state-of-the-art of the different aspects regarding PM resulting from brake wear and provide all the necessary information in terms of importance, physicochemical characteristics, emission factors and possible health effects.

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SEM images of brake wear particles (left <56 nm, middle PM2.5, right PM10). Source: [Kukutschová et al. 2011]
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Fig2: SEM images of brake wear particles (left <56 nm, middle PM2.5, right PM10). Source: [Kukutschová et al. 2011]

Mentions: The frictional contact between the disc and the pad generates particles of various sizes. During a braking event, the calliper acts mechanically on the pad, which slides against the disc and transforms vehicle kinetic energy into thermal energy. Apart from the mechanical abrasion, vehicle brakes become subject to large frictional heat generation with subsequent wear of linings and rotors. This generates mostly micron-sized particles. Figure 2 shows particles of different sizes generated as a result of brake wear tests performed in the laboratory (Kukutschová et al. 2011). Finally, some disc-brake systems require the pads to be in low-pressure contact with the rotor in order to ensure robust brake performance. This leads in higher particle release in the environment (Söderberg et al. 2008). A detailed explanatory model of the complex contact situation between an organic brake pad and a cast iron disc has been developed and published by some researchers (Eriksson et al. 2002; Österle et al. 2001; Ostermeyer 2001). In this model, the macroscopic friction and wear behaviour of a disc brake can be explained by the microscopic contact situation (growth and destruction of contact plateaus) in the boundary layer between the pad and disc. Wahlström (2011) provided a simplified visual explanation of the model which is given in Fig. 3. It has been shown that the plateau surface is covered by a nanocrystalline third body formed by the wear particles and that this third body is mainly made of iron oxides (Österle and Urban 2006). The third body differs in structure composition and properties from the two first bodies, pad and disc in our case (Oesterle and Dmitriev 2014). Much detailed work has been published on this field by several researchers (Bodel and Ostermeyer 2014; Ostermeyer 2007; Ostermeyer and Muller 2008).Fig. 2


Brake wear particle emissions: a review.

Grigoratos T, Martini G - Environ Sci Pollut Res Int (2014)

SEM images of brake wear particles (left <56 nm, middle PM2.5, right PM10). Source: [Kukutschová et al. 2011]
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4315878&req=5

Fig2: SEM images of brake wear particles (left <56 nm, middle PM2.5, right PM10). Source: [Kukutschová et al. 2011]
Mentions: The frictional contact between the disc and the pad generates particles of various sizes. During a braking event, the calliper acts mechanically on the pad, which slides against the disc and transforms vehicle kinetic energy into thermal energy. Apart from the mechanical abrasion, vehicle brakes become subject to large frictional heat generation with subsequent wear of linings and rotors. This generates mostly micron-sized particles. Figure 2 shows particles of different sizes generated as a result of brake wear tests performed in the laboratory (Kukutschová et al. 2011). Finally, some disc-brake systems require the pads to be in low-pressure contact with the rotor in order to ensure robust brake performance. This leads in higher particle release in the environment (Söderberg et al. 2008). A detailed explanatory model of the complex contact situation between an organic brake pad and a cast iron disc has been developed and published by some researchers (Eriksson et al. 2002; Österle et al. 2001; Ostermeyer 2001). In this model, the macroscopic friction and wear behaviour of a disc brake can be explained by the microscopic contact situation (growth and destruction of contact plateaus) in the boundary layer between the pad and disc. Wahlström (2011) provided a simplified visual explanation of the model which is given in Fig. 3. It has been shown that the plateau surface is covered by a nanocrystalline third body formed by the wear particles and that this third body is mainly made of iron oxides (Österle and Urban 2006). The third body differs in structure composition and properties from the two first bodies, pad and disc in our case (Oesterle and Dmitriev 2014). Much detailed work has been published on this field by several researchers (Bodel and Ostermeyer 2014; Ostermeyer 2007; Ostermeyer and Muller 2008).Fig. 2

Bottom Line: Among non-exhaust sources, brake wear can be a significant particulate matter (PM) contributor, particularly within areas with high traffic density and braking frequency.As exhaust emissions control become stricter, relative contributions of non-exhaust sources-and therefore brake wear-to traffic-related emissions will become more significant and will raise discussions on possible regulatory needs.The aim of the present literature review study is to present the state-of-the-art of the different aspects regarding PM resulting from brake wear and provide all the necessary information in terms of importance, physicochemical characteristics, emission factors and possible health effects.

View Article: PubMed Central - PubMed

Affiliation: European Commission, Joint Research Centre, Sustainable Transport Unit (STU), Institute for Energy and Transport (IET), Via E Fermi 2749, 21027, Ispra, Italy, theodoros.grigoratos@jrc.ec.europa.eu.

ABSTRACT
Traffic-related sources have been recognized as a significant contributor of particulate matter particularly within major cities. Exhaust and non-exhaust traffic-related sources are estimated to contribute almost equally to traffic-related PM10 emissions. Non-exhaust particles can be generated either from non-exhaust sources such as brake, tyre, clutch and road surface wear or already exist in the form of deposited material at the roadside and become resuspended due to traffic-induced turbulence. Among non-exhaust sources, brake wear can be a significant particulate matter (PM) contributor, particularly within areas with high traffic density and braking frequency. Studies mention that in urban environments, brake wear can contribute up to 55 % by mass to total non-exhaust traffic-related PM10 emissions and up to 21 % by mass to total traffic-related PM10 emissions, while in freeways, this contribution is lower due to lower braking frequency. As exhaust emissions control become stricter, relative contributions of non-exhaust sources-and therefore brake wear-to traffic-related emissions will become more significant and will raise discussions on possible regulatory needs. The aim of the present literature review study is to present the state-of-the-art of the different aspects regarding PM resulting from brake wear and provide all the necessary information in terms of importance, physicochemical characteristics, emission factors and possible health effects.

Show MeSH