Development and application of an analytical method for the quantification of tire wear in atmospheric deposition

Abstract. Tire wear particles (TWP) are a major source of microplastic pollution and a carrier of rubber additives and metal-containing compounds that can be released into the environment and adversely affect ecosystems. Reliable quantification of TWP remains challenging because tire materials are compositionally heterogeneous and environmental samples contain complex organic and inorganic matrices that interfere with their analysis. Here, we present a pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) method for the quantification of TWP in atmospheric deposition samples. The method combines targeted sample pretreatment, including density separation and removal of organic matrix components, with the analysis of six characteristic pyrolysis products of tire rubber, namely butadiene, 4-vinylcyclohexene, isoprene, limonene, styrene, and α-methylstyrene. The sum of the integrated peak areas of these markers is used to quantify TWP mass.

Instrumental parameters, including pyrolysis temperature (set to 500 °C) and gas chromatographic separation, were systematically optimized to maximize sensitivity, reproducibility, and chromatographic resolution. Calibration was established using cryo-milled tread materials from 23 used passenger car and truck/bus tires as well as a mixture of cryo-milled tread materials representative of the U.S. tire market. The sum of the six marker signals showed a strong linear relationship with tire tread mass across different tire types (r² = 0.93). The method achieved a limit of detection of 0.16 µg TWP and a dynamic range extending to approximately 450 µg TWP. A comprehensive uncertainty assessment identified variability in tire composition as the dominant source of uncertainty. The expanded uncertainty for the quantification of TWP in a single atmospheric deposition sample ranged from −58 % to +63 %.

Application of the method to duplicate atmospheric deposition samples collected at two suburban sites demonstrated its suitability for environmental monitoring. Mean TWP mass deposition rates of 843.9 µg m⁻² day⁻¹ were measured at a site located near a busy road, compared with 253.4 µg m⁻² day⁻¹ at a nearby suburban background site. These results demonstrate that the proposed multi-marker Py-GC-MS approach enables quantitative TWP measurements in complex environmental samples while providing an explicit characterization of the associated measurement uncertainty.