Emissions of Volatile Organic Compounds from Brake Wear and Their Role in Ultrafine Particle Nucleation

Olivier Durif; Lucas Bard; Karine Elihn; Barbara Nozière; Ulf Olofsson; Sarah S Steimer

doi:10.1021/acsestair.5c00070

Emissions of Volatile Organic Compounds from Brake Wear and Their Role in Ultrafine Particle Nucleation

ACS EST Air. 2025 Jun 11;2(7):1308-1314. doi: 10.1021/acsestair.5c00070. eCollection 2025 Jul 11.

Authors

Olivier Durif¹, Lucas Bard², Karine Elihn³, Barbara Nozière¹, Ulf Olofsson², Sarah S Steimer^{3

4}

Affiliations

¹ Department of Chemistry, KTH, Royal Institute of Technology, Stockholm 10044, Sweden.
² Department of Machine Design, KTH, Royal Institute of Technology, Stockholm 10044, Sweden.
³ Department of Environmental Science, Stockholm University, Stockholm 11418, Sweden.
⁴ Bolin Centre for Climate Research, Stockholm 11418, Sweden.

Abstract

The emission of volatile organic compounds (VOCs) from brake wear is a relatively underexplored aspect of nonexhaust traffic emissions. We employed a proton-transfer-reaction time-of-flight mass spectrometer to investigate the real-time emissions of VOCs from two commercially prevalent brake materials: low-metallic copper-free (LMCF) and nonasbestos organic (NAO). Experiments were conducted using a pin-on-a-disc tribometer integrated with a fast-mobility particle sizer spectrometer. The results reveal that NAO brake pads emit higher concentrations of VOCs than LMCF pads. Over 200 different sum formulas were identified for both materials, and siloxanes were observed as characteristic of NAO emissions. The ultrafine particle formation was systematically preceded by an increase in gaseous emissions. This observation supports the thesis that ultrafine particle formation emitted by brake wear occurs through VOCs nucleation, addressing a significant gap in the literature.

Keywords: Brake wear; FMPS; LMCF; NAO; PTR-TOF-MS; Tribology; Ultra fine particle; VOCs.