Exhaust filters not doing (ultra)fine 

Exhaust filters not doing (ultra)fine 

I’m usually a positive person, always ready to crack a joke … but a new study from the University of Birmingham (along with some stats from this article) is no laughing matter. The issue has me feeling rather negative about every breath we take.

I was startled to read the study “Limited impact of diesel particle filters on road traffic emissions of ultrafine particles”, published in Environmental International. It found that the filters fitted to vehicle exhaust systems to remove particulate matter pollution have limited impact on ultrafine particles.

The filters are able to remove the majority of larger, solid particles, but the new study shows they are less effective at removing smaller liquid particles.

While the World Health Organization (WHO) has not yet set a guideline for safe levels of ultrafine particles, it recognises that overall, particulate pollution is associated with negative impacts on cardiovascular and respiratory health. Air quality guidelines published by the WHO in 2021 also outline concerns over ultrafine particles and their ability to be transported around the body.

Lead author on the study, Professor Roy Harrison, says: “Our research shows clearly that current, widely-used filters are not effective against these smaller particles, and we welcome recommendations from the World Health Organization that surveillance of these measurements increase and note with concern that current concentrations measured in London are classified as ‘high’.”

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

The data showed a steep decline in larger particles. Black carbon, for example, declined by 81% between 2014 and 2021. This is a clear indication that there has been a positive impact from the introduction of exhaust filters.

In contrast, however, the number of particles described as “ultrafine” – smaller than 100 nanometres – reduced by only 26%. The smallest group of particles, measuring less than 30 nanometres, did not reduce at all, giving a clear indication that filters are not effective against these types of particles.

WHO guidelines define concentrations of ultrafine particles above 10,000/cm³ as “high” and concentrations measured at the Marylebone Road site were around twice this level. Just imagine what the levels would be in Johannesburg.

“High concentrations of ultrafine particles are likely to be a widespread and persistent phenomenon. In order to meet WHO guidelines we are likely to need a much higher uptake of electric vehicles, as well as additional measures to reduce emissions from diesel vehicles,” notes Harrison.

This solution will work really well in South Africa, where our electricity is mainly generated (if and when it’s on) from coal-burning power plants that would – under Eskom’s current plans – be responsible for 79,500 air pollution related deaths between 2025 and the plants’ planned end-of-life (more about that here).

But let’s stay calm and take a deep breath. Oh, wait …

Published by

Jaco de Klerk

JACO DE KLERK is editor of SHEQ MANAGEMENT and assistant editor of its sister publication FOCUS on Transport and Logistics. It’s nearly a decade later, and he is still as passionate about all things SHEQ-related since his first column, Sound Off, which he wrote for this magazine as well.
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