Vehicle exhaust filters don’t remove “ultrafine” pollution – new study

Airborne particles from vehicle emissions are a major contributor to air pollution levels. Exhaust filters designed to combat this pollution have been required by law in new cars since 2011 and in heavy-duty vehicles since 2013.

The filters can remove most larger, solid particles, but the new studypublished in Environment International, shows that they are less effective in removing smaller liquid particles.

While the World Health Organization has not yet issued a guideline for safe levels of ultrafine particles, it recognizes that particulate pollution is generally associated with adverse effects on cardiovascular and respiratory health. Air quality guidelines published by WHO in 2021 also outline concerns about ultrafine particles and their ability to be transported throughout the body.

Lead author of the study, Professor Roy Harrison, said: “Our research clearly shows that current, commonly used filters are ineffective against these smaller particles and we welcome recommendations of the World Health Organization that the monitoring of these measurements is increasing and notes with concern that the current concentrations measured in London are classified as ‘high’.”

“High concentrations of ultrafine particles are likely to be a widespread and persistent phenomenon. To meet WHO guidelines, we probably need much greater adoption of electric vehicles, as well as additional measures to reduce emissions from diesel vehicles.” —Professor Roy Harrison, School of Geography, Earth and Environmental Sciences

The team used data collected from a monitoring station in London’s Marylebone Road. Air quality sampling at this site has produced the most comprehensive long-term data set in the world, with mass and particle count data dating back to 2010.

The data showed a sharp decrease in larger particles. Black carbon, for example, fell by 81% between 2014 and 2021. This is a clear indication that there is a positive effect of the introduction of exhaust filters.

In contrast, the number of particles described as “ultrafine” – smaller than 100 nanometers – has been reduced by only 26%. The smallest group of particles, smaller than 30 nanometers, did not decrease at all, which is a clear indication that filters are not effective against these types of particles. WHO guidelines define concentrations of ultrafine particles above 10,000 per cubic cm as “high” and concentrations measured at the Marylebone Road site were about double this level.

Professor Harrison added: “High concentrations of ultrafine particles are likely to be a widespread and ongoing phenomenon. To meet WHO guidelines, we probably need a lot higher adoption of electric vehiclesas well as additional measures to reduce emissions from diesel vehicles.”

The University of Birmingham ranks among the top 100 institutions in the world. The work brings people from all over the world to Birmingham, including researchers, teachers and more than 6,500 international students from more than 150 countries. Harrison et al. (2023). “Limited impact of soot filters on road traffic emissions of ultrafine particles.” Environment International

Featured image courtesy of Khunkorn Laowisit, Pexels

Related story: Study links Adoption of electric vehicles with less air pollution and improved health

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