Development of an analytical procedure for the characterization of the particulate matter emitted by the braking system.

Brake wear particulate matter (PM) is a relevant source of non-exhaust emissions, but its inorganic characterization remains analytically challenging because of the heterogeneous composition of friction materials and the low concentrations of several target analytes. In this work, a multitechnique analytical workflow was developed for the characterization of the composition of PM10 generated by WLTP-based brake dynamometer tests. Thirty-two PM10 samples were collected from tribological couples involving low-steel (LS) and non-asbestos organic (NAO) pads combined with grey cast-iron (GCI) or coated discs. A combined acid digestion strategy based on HNO3/H2O2 and HNO3/HF/H3BO3 mixtures was validated using SRM NIST 1648a, determining multi-elemental composition by ICP-OES and ICP-MS. The procedure enabled quantification of 27 elements and improved elemental coverage of the PM10, with recoveries over 75 % for most of the analytes. LS-GCI systems showed the highest PM10 emission factors, whereas NAO-GCI showed the lowest. Fe dominated LS-derived PM10, while Ba, Ti, K, and Zr were more characteristic of NAO-derived samples. Investigation considering Mn-based enrichment factor improved discrimination between rotor- and pad-related contributions. FESEM-EDS confirmed the main compositional trends at the particle scale, and chemometric elaboration (PCA/HCA) enabled clear separation of tribological families according to pad formulation and disc type. The proposed workflow provides a robust analytical basis for the characterization of brake wear PM10 together with the identification of source-related elemental markers in non-exhaust emission studies.