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New research has revealed that construction activity is now a dominant source of black carbon emissions in central London. The research, published in the journal , is the first of its kind in Europe.

While pollution levels from road traffic have fallen significantly thanks to policies like the Ultra Low Emission Zone (ULEZ), new air pollution data from scientists at the University of Manchester, in collaboration with the UK Center for Ecology & Hydrology (UKCEH), University of York, Zhejiang University and National Center for Atmospheric Science, reveal emissions from non-road mobile machinery, such as generators and heavy-duty construction equipment, can exceed those from vehicles, particularly in areas where there is a lot of building activity.

Black carbon is soot from combustion and is a component of particulate matter (PM_2.5). These are very fine particles that can enter the lungs and bloodstream and are known to damage human health.

The team collected the pollution measurements from the top of the BT Tower in central London over summer and winter, using a technique called eddy covariance to track how much black carbon is released into the air and where it comes from.

The findings revealed that while pollution levels were significantly lower than cities like Beijing and Delhi, which have monitored pollution using the same method, they are not low enough to meet the World Health Organization's guidelines for PM_2.5. They suggest similar regulatory attention to road traffic is now needed for the construction sector.

"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," says Dr. James Allan.

At 190 meters tall, the BT Tower observatory has a specialized gas inlet system installed on the tower's roof, which draws air into a laboratory on the 35th floor, allowing researchers to analyze pollution as it rises from streets, buildings, construction sites and nearby parks below.

The 'eddy covariance' method works by measuring the turbulent motion of air, also known as eddies, and the concentration of airborne substances like black carbon within those eddies.

The scientists also conducted a detailed spatial footprint analysis to pinpoint emission hotspots that were directly linked to active construction sites near the BT Tower.

The new findings suggest that further progress in improving London's air quality will require stricter regulation of construction machinery, especially in rapidly developing areas.

Dr. Allen added, "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."