Application of Mass Spectrometry Techniques to Study Tire Wear Particles and Associated Chemical Additives: From Laboratory Investigations to Field Studies
Xing Wang, Michael A.R. Tawadrous, Bonnie Hamilton, Chelsea Rochman, Colman Wong, Yushan Su, Greg J. Evans, Arthur W. H. Chan, ALEX K.Y. LEE, Environment and Climate Change Canada
Abstract Number: 397
Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts
Abstract
Non-exhaust vehicular emissions are increasingly important as a source of air pollutants. Abrasion of vehicle tires can generate airborne particulate matter, but the chemical characterization has been limited. In this work, we aim to develop online and offline mass spectrometry techniques to study the chemical composition of tire wear particles, in order to quantify their contribution to near-road air pollution and investigate the fate and transformation of tire additives.
In our laboratory investigation, a soot particle aerosol mass spectrometer (SP-AMS) was used to study tire wear particles generated by grinding old tire treads. The mass spectra of such airborne tire wear particles resemble those of tire tread rubbers measured by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) and hydrocarbon-like organic aerosols (HOA) that are largely associated with traffic activities. Carbon blacks are widely used as reinforcing fillers in tires, and they can be found in road dust with tire rubber. Nevertheless, no detectable amounts of refractory black carbon (rBC) signals were observed during the laser vaporization mode of SP-AMS measurement, suggesting that carbon blacks were unlikely co-emitted with tire nano-rubber into the air in our experiments. This work also developed a workflow incorporating microwave assisted extraction into Py-GC/MS analysis to identify the polymeric composition and tire additives (e.g. antioxidants) in tire tread. Levels of chemical additives in tire wear debris are highly variable, while the rubber content varies by a factor of 1-2. Applying Py-GC/MS analysis to measure the rubber contents in air samples adjacent to a busy highway, we estimate the contribution of tire wear particles to total suspended particles and survey the dynamics of chemical additives in the near road environment.