Evaluation of Hydrogenated Resin Acids as Molecular Markers for Tire-wear Debris in Urban Environments

To propose new molecular markers for tire-wear emissions, four dihydroresin acids, that is, 8-isopimaren-18-oic acid (I), 8-pimaren-18-oic acid (II), 13 beta(H)-abieten-18-oic acid (Ill), and 13 alpha(H)-abiet-8-en-18-oic acid (IV), were identified and investigated for source specificities, distributions, and environmental stabilities. The absence of I IV in natural sources and the linear correlation's between dihydroresin acids with different skeletons in tires and in environmental samples demonstrated that I IV are specific markers for synthetic rubbers. The ratio of III + IV to the sum of III + IV plus abietic acid showed the resin acids distribution between different environmental compartments receiving contributions from traffic and natural sources. The physicochemical properties and results of photolysis experiments suggested that I-IV can set lower limits for tire-wear contributions to environmental loads of particulate matter (PM) and;polycyclic aromatic hydrocarbons with molecular weight >= 202. By comparing III + IV concentrations or (III+IV)/pyrene or (III+IV)/benzo[a]pyrene ratios in tires and those in environmental matrices, the contributions of tire-wear emissions to PM pyrene and:benzo [a]pyrene were estimated to be 0.68 +/- 0.54%, 6.9 +/- 4.8%, and 0.37 +/- 0.18% in roadside PM and 0.83 +/- 0.21%, 0.88 +/- 0.52%, and 0.08 +/- 0.06% in rooftop PM.