Aerosol release from abrasion of nano-TiO2 pavements and tires containing nano-SiO2
Résumé
Nanoparticle release due to the abrasion process can have a drastic consequence on inhalation exposure. Indeed, emissions caused by tire wear on trafficked roads is now identified as a major aerosol source (Yan 2014). The nanoparticle introduction in pavements or tires respectively as nano- TiO2 or nano-SiO2 is an obvious concern because of the inhalation risk of these nanoparticles. One part of the studies presented here Nano-Data project is devoted to define more precisely this risk according to a standardized test developed in the field. To do so, a standardized wearing test called Wehner and Schulz (Do 2007) giving the normalized friction coefficient of the road pavements (NF EN ISO 16474-1 2014) has been performed on 9 marketed pavements containing nano-TiO2. In the present essays, a silica dispersion is used to polish the sample surface and to observe the nanomaterial behavior. During polishing test the silica dispersion is enriched by pavement fragments in which we note a low presence of titanium in composites formed of nano-TiO2 included in a cement matrix. The absence of free nano-TiO2 release has to be highlighted. The dispersions sampled during the process and analyzed by TXRF show no significant increase in the concentration of titanium but low concentration of calcium increases during the polishing progress. Analyzes of filtered dispersions proved than no object below 0.45 μm is detected and confirm the absence of free nanoparticle release. Another test called FABAC (Figure 1) which involves the direct contact between tires and pavements has been used to simulate road traffic. Tires are supposed to mostly generate big objects of 5- 25 μm (Kreider 2010). However, Sjödin et al. mention submicronic emissions while tires are accelerating or decelerating (Sjödin 2010). In the present work, two types of tire have been tested: one with a classical formulation, the other enriched with nano-SiO2. Two kinds of pavements have been also used: one with nano-TiO2, the other without. The aerosols produced during the wearing of tires on pavements have been characterized by APS/SMPS and TEM sampling. In all the obtained results from FABAC tests, the main mode of the aerosol particles is lower than 30 nm. No debris from pavement has been distinguished on TEM grid. However submicronic or nanometric tire debris containing carbon, silicon and zinc have been collected and characterized. The FABAC solicitation consists in successive impacts which could be assimilated to acceleration or deceleration phases and could explain, according to the literature, releases of submicronic tire particles (Sjödin 2010; Mathissen 2011).