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

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 (PM) 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 PM at median concentrations of 212 pg/m for 1,3-diphenylguanidine (DPG) and 132 pg/m 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/m, 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 PM did not agree to the pattern found for cryo-milled tire tread (CMTT), likely reflecting transformation processes in tires or the aerosol and the influence from other sources than TRWP. Concentrations in PM were determined from one of the sites and were by a factor of 4 - 10 lower than in PM for 9 compounds, but a few others, mostly benzothiazoles showed similar or higher concentrations. Many of the tire-related chemicals were also determined in PM 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 PM and PM aerosol and requires scrutiny with respect to its relevance for human exposure.