Traceable determination of metal composition of tyres using tandem ICP-MS and benchmarking of emissions inventories.

Non-exhaust emissions are becoming of increasing significance with respect to total particulate matter (PM) concentrations in ambient air. Of particular interest is the metal content of this PM since metallic compounds are well known to have toxic effects on human health and the environment. In this study, 'bottom-up' annual tyre wear emission rates were estimated and compared to top-down' emissions declared by the UK; it was calculated that between 14 and 25 tonnes of Zn entered the atmosphere in PM10 in 2020. The emission rates were estimated using a cost-effective, simple but robust validated method for analysis of the metals in tyres using tandem inductively coupled plasma mass spectrometry (ICP-MS/MS) for the first time, involving minimal offline sample preparation. This method was applied to five different tyre makes and brands, all available for sale in the UK, and the uncertainty of each measurement was determined. Traceability was ensured in all methods and novel validation techniques were applied due to lack of available reference materials. Zn was found to be the largest metal component in all tyres with a mass fraction of approximately 10 mg g-1. The mean mass fractions of metals in the tyres decreased in the order of Zn > Al > Fe > Mg > Ti > Pb > Cu > Ba > Ni. Significant differences in composition were found between the five tyres. The relative expanded uncertainties of the metals measurements ranged from 4 to 21%, with elements of higher mass fraction resulting in lower uncertainties. These findings will contribute to assessing current and future air quality challenges and will help to inform regulation surrounding non-exhaust emissions.

Multi-element analysis of tyre rubber for metal tracers.

The purpose of this study was to identify a characteristic elemental tyre fingerprint that can be utilised in atmospheric source apportionment calculations. Currently zinc is widely used as a single element tracer to quantify tyre wear, however several authors have highlighted issues with this approach. To overcome this, tyre rubber tread was digested and has been analysed for 25 elements by ICP-MS to generate a multielement profile. Additionally, to estimate the percentage of the tyre made up of inert fillers, thermogravimetric analysis was performed on a subset. Comparisons were made between passenger car and heavy goods vehicle tyre composition, and a subset of tyres had both tread and sidewall sampled for further comparison. 19 of the 25 elements were detected in the analysis. The mean mass fraction of zinc detected was 11.17 g/kg, consistent with previous estimates of 1% of the tyre mass. Aluminium, iron, and magnesium were found to be the next most abundant elements. Only one source profile for tyre wear exists in both the US and EU air pollution species profile databases, highlighting the need for more recent data with better coverage of tyre makes and models. This study provides data on new tyres which are currently operating on-road in Europe and is therefore relevant for ongoing atmospheric studies assessing the levels of tyre wear particles in urban areas.