A new study suggests that if cities want to continue to drive down levels of black carbon, they should switch their efforts from road transport to construction equipment.
The research, conducted at the top of the BT Tower in London, was undertaken by a team involving scientists from the University of Manchester, UK Centre for Ecology and Hydrology, University of York, Zhejiang University, and the National Centre for Atmospheric Science.
The study looked at how much black carbon – which is essentially soot – is released into the air in central London during both summer and winter. Black carbon is emitted alongside other air pollutants during incomplete combustion and while its sources can range from brick kilns to residential energy and wildfires, in cities the major source has traditionally been road traffic.
In the BT Tower’s observatory, 35 floors up, the team collected air samples as they rose from the streets and buildings below. Using a method called eddy covariance, they could directly measure the pollution as it moved through the air in real-time.
This technique involves measuring wind speed and direction as well as the concentration of black carbon particles. By combining these two measurements, they can calculate the flux – the rate at which it is moving through the air. If more black carbon is going up than coming down, the area below the tower is a source of black carbon.
When black carbon in this area was measured in 2012, road traffic was clearly the predominant source but this is not the case now. Instead, the non-road mobile machinery (NRMM) used on construction sites – which are subject to far less stringent emission regulations than cars – have become a much more significant emitter, especially in areas with a higher concentration of construction work.
Dr James Allan, senior research scientist at the National Centre for Atmospheric Science and University of Manchester said: ‘We found only minimal emissions from traffic, which is consistent with emissions reductions associated with Euro 6, the standard for diesel engines specified by ULEZ.
‘This is in contrast to previous measurements in London, collected in 2012, which showed a strong association between traffic and black carbon. At the time, diesel particle filters had only been introduced relatively recently. And while domestic wood burning is also known to be a source of black carbon in the UK, this was predictably not found to be the case in central London which is mainly commercial rather than residential.’
‘We compared observed emissions with emission standards for construction equipment and found that even with compliance, black carbon output from generators, machinery and construction vehicles remains significant. Our work highlights how measurement techniques like eddy covariance can fill critical gaps in our understanding of urban pollution and support evidence-based strategies to protect public health and the environment.’
The full research can be read here.
Photo: TheOtherKev
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