The impact of road-tire wear: a hidden source of airborne microplastics and black carbon

A major source for airborne microplastic particles is road-tire wear. Microscopy and chemical analyses of wind-blown particles on dirty, high-elevation (2865-3690 m) snow surfaces in the Colorado Rocky Mountains revealed the presence of black carbonaceous substances intimately mixed with microplastics, particles interpreted as tire matter.

Identical and similar particles occur in shredded tires and in samples collected from road surfaces. The black substance responsible for the black color of all tire particles is nano-size carbon black, a tire additive that homogeneously permeates tire polymers and other additives and that strongly absorbs solar radiation .

The key to documentation of worn tire matter was the identification in two-dimensional gas chromatography by Emissions Analytics of many organic compounds in snow common to those in road tires. The mass of black carbonaceous particles produced by road-tire wear may be estimated by multiplying measured mass of eroded tire-per-distance traveled by vehicular distances. The eroded tire mass from moving vehicles used for these estimates was measured by Emissions Analytics.

Under assumptions of amounts of tire-wear particles emitted to the atmosphere, the mass proportion of atmospheric black carbonaceous matter from annual road-tire wear might be as much as about 10-30% of atmospheric black carbon, such as soot from vehicle exhaust and domestic cooking. Black particles from road-tire wear may thus be an important component that contributes to melting of snow and ice as well as to warming the atmosphere. The potential toxicity of organic compounds in black-tire matter is another concern for the health of organisms in mountain ecosystems. A revised estimate for the annual mass of eroded tires globally is 6550 kilotonnes.

Citation:

Reynolds, R. L., Molden, N., Kokaly, R. F., Lowers, H., Breit, G. N., Goldstein, H. L., Williams, E. K., Lawrence, C. R., & Derry, J. (2024). Microplastic and Associated Black Particles from Road-tire Wear: Implications for Radiative Effects across the Cryosphere and in the Atmosphere. Journal of Geophysical Research: Atmospheres, 129, e2024JD041116, https://doi.org/10.1029/2024JD041116

Low Emission Bus Trial in the Republic of Ireland

One of the big contributors to poor urban quality, both for nitrogen oxides (NO_x) and particulates has historically been bus fleets. However, Emissions Analytics’ experience across multiple types of vehicle, from light- to heavy-duty, has been that performance can differ markedly from model to model of seemingly similar technologies, and also between official figures and the reality of performance on the road.

To improve urban quality, Ireland’s National Development Plan committed the country to stop purchasing diesel-only buses for the urban public fleet by July 2019. To ensure that it make the best purchasing decisions in order to achieve that objective in the most effective way, the Irish Department for Transport, Tourism and Sport (DTTAS) commissioned Emissions Analytics to test eleven different types of bus in realistic conditions in Dublin and Cork. Emissions Analytics’ independence ensured that unbiased, real-world data could be gathered, rather than relying on existing third-party information.

The test equipment proposed by Emissions Analytics, largely relied on a Portable Emissions Measurement System (PEMS) from Sensors, Inc of the USA. The unit was certified to the standards required when used for official certification in Europe, even though these tests were not regulatory tests. The equipment passively measures both the flow of gas and pollutant concentrations from the bus tailpipe.

The buses tested ranged from existing diesels on the fleet such as the 2008 and 2013 Volvo B9TL, and the 2018 Mercedes-Benz Citaro BlueTEC 6, through to a new diesel Wrightbus Streetdeck Hybrid and a new Scanio Enviro 400 CBG powered by natural gas. Also covered were retrofits to these existing Volvos to understand the effectiveness of the after-market installations of Selective Catalytic Reduction (SCR) systems aimed at reducing NO_x emissions.

Together with DTTAS and consultants Byrne Ó’Cléirigh (BOC), Emissions Analytics designed test cycles on the road of Dublin and Cork, based closely on existing bus routes. As the buses were tested when not in public operation with passengers, it was necessary to mimic the behaviour around regular bus stops to ensure that the average speeds and dynamicity of the cycles mirrored as closely as possible the reality of typical live operation. Taking this one step further, results were gathered for ‘cold start’ operation, where emissions are typically higher as the bus is warming up from cold, and also during regeneration of the diesel particulate filter, which similar leads to heightened emissions.

While the focus was on reducing pollution from NO_x and particle emissions, the test programme covered a wider range of measurements to give a more holistic view. Other pollutants measured were carbon monoxide and, where relevant, total hydrocarbons. Relevant to the greenhouse gas agenda, carbon dioxide was measured, from which, using the carbon balance methods, the fuel consumption was derived. In this way, a rounded view on pollution and operation cost was formed, thereby ensuring that decisions around reduction of certain pollutants did not lead to unintended other consequences.

The final report detailing the findings from the trial has now been published.

EMIS hearing, 20 June 2016 Questions to Emissions Analytics

Euro 6 on-road testing ICCT technical report 20160929

In 2015, the ICCT commissioned Emissions Analytics, a commercial test house specializing in testing real-world fuel consumption and emissions, to perform on-road testing of Euro 6-regulated gasoline and diesel vehicles. Emissions Analytics tested 7 vehicles between 2015 and 2016 for emissions of carbon monoxide (CO), carbon dioxide (CO2), nitric oxide (NO), nitrogen dioxide (NO2), and particulates. The vehicles selected for testing were a Ford Focus, Volkswagen Golf, Citroën C4, Mercedes-Benz C220, Vauxhall/Opel Astra, Volkswagen Transporter and Volkswagen Caddy C20. The Ford Focus and the Volkswagen Golf were gasoline direct injection vehicles, while the rest were diesel. The detailed testing results can be found in the full report available below.