Quantification and occurrence of 39 tire-related chemicals in urban and rural aerosol from Saxony, Germany

Abstract

Tire and road wear particles (TRWP) are a major contributor to non-exhaust traffic emissions, but their contribution to and dynamics in urban aerosol is not well known. Urban particulate matter (PM) in the size fraction below 10 µm (PM₁₀) from two German cities was collected over 2 weeks and analysed for 39 tire-related chemicals, including amines, guanidines, ureas, benzothiazoles, p-phenylenediamines, quinolines and several transformation products (TPs). Of these, 37 compounds were determined in PM₁₀ at median concentrations of 212 pg/m³ for 1,3-diphenylguanidine (DPG) and 132 pg/m³ for benzothiazole-2-sulfonic acid (BTSA); 10 of the compounds have not been reported in urban aerosol before. Median concentrations of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD), 6-PPD quinone (6-PPDQ), and 1,2-dihydro-2,2,4-trimethylquinoline (TMQ) were 1.0, 4.1, and 8.1 pg/m³, respectively. Some parent compounds showed positive correlation with their TPs, e.g. 6-PPD with 4-aminodiphenylamine (4-ADPA), N,N’-diphenyl-p-phenylenediamine (DPPD) with DPPD quinone (DPPDQ), and DPG with phenylguanidine (PG). The concentration pattern of the compounds in PM₁₀ did not agree to the pattern found for cryo-milled tire tread (CMTT_mix), likely reflecting transformation processes in tires or the aerosol and the influence from other sources than TRWP. Concentrations in PM_2.5 were determined from one of the sites and were by a factor of 4 – 10 lower than in PM_10-2.5 for 9 compounds, but a few others, mostly benzothiazoles showed similar or higher concentrations. Many of the tire-related chemicals were also determined in PM₁₀ of one rural site, although at median concentrations up to two orders of magnitude lower. A large number of tire chemicals with a wide concentration range is present in urban PM₁₀ and PM_2.5 aerosol and requires scrutiny with respect to its relevance for human exposure.