PM EMISSIONS FROM TYRES AND BRAKES MAIN FACTS AND OPEN ISSUES Sustainable Transport Unit Institute for Energy and Transport Joint Research Centre 04 April 2014 T. Grigoratos and G. Martini

IMPORTANCE AND FACTORS AFFECTING WEAR PARTICLES MASS SIZE AND PARTICLE NUMBER DISTRIBUTIONS CHEMICAL CONSTITUENTS OF WEAR PARTICLES BRAKE AND TYRE WEAR EMISSION FACTORS

IMPORTANCE AND FACTORS AFFECTING WEAR PARTICLES

Contribution of brake and tyre wear to non-exhaust traffic-related PM 10 emissions * Lower contribution of brake wear in freeways (~ 3%) ** Many studies don’t distinguish tyre from road wear

 Tyre wear particles contribute ~0.8-7% by mass to ambient PM 10. This corresponds to ambient concentrations of μg m -3  No estimations regarding the contribution of brake wear to ambient PM 10 were found Contribution of tyre wear particles to ambient PM 10 (%)

 The conditions under which the braking event occurs (vehicle’s speed, environmental temperature, chemicals)  The driving behavior (severity & frequency of braking events) BRAKES  Tyre characteristics  Road surface characteristics  Vehicle characteristics TYRES Tyres and pavement interaction alters the characteristics of wear particles

 Lack of standardized sampling methodologies. Different sampling methods result in non comparable - contradictory results and conclusions Brakes location (front or rear) Brakes type (i.e. metallic, NAO) Laboratory or on-road sampling Close or open sampling system Tyres location (front or rear) Tyres type (i.e. friction, studded) Laboratory or on-road sampling  There is no definition of “normal” or “typical” driving conditions Steady state with km h -1 Accelerations of < m s -2 Decelerations of < m s -2 Full stop braking km h -1 TYRES BRAKES

MASS SIZE AND PARTICLE NUMBER DISTRIBUTIONS OF WEAR PARTICLES

 40-50% by mass of generated brake wear particles is emitted as PM 10. Among it ~ 50% by mass or more is PM 2.5  Brake wear PM 10 distributions are unimodal (peak at 2-6 μm) [Examples adopted from: Left - Iijima et al., 2007; Right – Kukutschová et al., 2011] BRAKES  % by mass of generated tyre wear particles is emitted as PM 10  PM 10 mass distribution is shifted towards larger sizes with studded tyres TYRES

 Bimodal and unimodal distributions for tyre wear PM 10. Different type of tyres and sampling procedures or limitations in instrumentation used [Up - Gustafsson et al., 2008; Down – Kwak et al., 2013] References regarding mass size distribution of tyre wear

References regarding PN distribution of tyre wear  Particle number distributions of tyre wear particles are unimodal  At least one peak of brake wear PN distribution lies within PM 2.5 References regarding PN distribution of brake wear

 There are studies which demonstrate bimodal PN distributions with a 2 nd peak at PM 2.5  Not all researchers find the 1 st peak at the UF size BRAKES  Not clear whether there is UF particle production with friction and summer tyres and if yes under which conditions TYRES

CHEMICAL CONSTITUENTS OF WEAR PARTICLES

 The most common key tracers of brake wear is Cu Chemical constituents of brake wearChemical constituents of tyre wear  The most common key tracers of tyre wear are:

 Lack of information regarding specific organic constituents of brake and tyre wear PM 10. Some research has been conducted for wear particles  Some researchers mention that brake wear is an important source of Sb in the environment, while others have not found it in brake wear PM 10 Organic constituents of brake and tyre wear debris

CHEMICAL CONSTITUENTS OF WEAR PARTICLES BRAKE AND TYRE WEAR EMISSION FACTORS

 PM 10 EFs of HDVs are one order of magnitude higher compared to LDVs  PM 10 EFs of brake wear for LDVs are close to the Euro 4/5 standard PM 10 emission factors of brake wear found in the literature (mg km -1 vehicle -1 )

 PM 10 EFs of HDVs are one order of magnitude higher than LDVs  Much higher PM 10 EFs have been reported in case of studded tyres  PM 10 EFs of tyre wear for LDVs are close to the Euro 4/5 standard PM 10 emission factors of tyre wear found in the literature (mg km -1 vehicle -1 )

 The friction materials used in clutch linings are similar to those used in brake linings  Existing studies are rather old and were conducted with asbestos-based clutches. This material has been replaced in modern clutches  There appears to be no recent information relating to the amount of material lost to the environment or PM emissions from this source  The enclosed nature of the clutch mechanism probably means that much of the wear material is retained inside the housing. However, further investigation is necessary

 Contribution of brake and tyre wear to ambient PM 10  Representativeness of “real-world” emissions – Harmonized sampling procedures in order to have comparable results  Definition of “typical” driving conditions  UF particles generation with friction tyres – if yes, under what conditions  Organic constituents of PM 10 and PM 2.5 wear particles  Possible benefit of a reduction in PM 10 emission factors