Research on the air in London suggests the ultra low emission zone (Ulez) may be working better than expected, but the heating of buildings may become a barrier to reducing air pollution.
The research was done from the top of the BT Tower. Sam Cliff, of the University of York, said: “The observatory is a tiny room, 35 floors up, surrounded by telecommunications kit and crammed full of scientific instruments. The view is great but on windy days maintenance can be really challenging.” From the top of the tower, Cliff measured air pollution drifting upwards from the streets and buildings below, allowing him to gradually map the sources within about 3.5km.
Air pollution hotspots included the buses and taxis feeding Euston station, the congested streets around Oxford Street and Piccadilly, and the combined heating and power generation systems in Bloomsbury.
Covid restrictions and home working during 2020 and 2021 completely changed air pollution in central London. A 32% decrease in carbon dioxide rising from around BT Tower allowed Cliff and the team to estimate the improvements in air pollution that should have resulted from the reduction in fuel use. But the Covid-induced changes were bigger. There was a 73% decrease in nitrogen oxides, the group of pollutants that includes nitrogen dioxide, levels of which regularly break legal limits on the streets below.
Predicted changes from the Ulez were added to those expected from less fuel use. The Ulez appeared to be working at least as well as expected, if not better. Another factor was less congestion on the roads below, meaning less stop-start and less slow-moving traffic. This led Cliff and team to conclude that traffic reduction in combination with Ulez-type schemes would be an optimal policy for public health, especially if road space was then given over to walking and cycling.
The Covid period also gave us a glimpse of future air pollution as road transport is electrified but heating buildings with fossil gas may remain. Building heating is already the largest source of nitrogen oxides in London’s financial district. This is not a unique problem. By 2030, home heating is expected to exceed traffic as the main source of nitrogen oxides in the city of York.
It is possible that hydrogen will replace fossil gas heating in future, but burning hydrogen still produces nitrogen oxides.
Prof Ally Lewis, of the National Centre for Atmospheric Science, said: “Getting combustion out of cities is central to further improving air quality in the UK. This means tackling more than just wood-burning stoves. Burning natural gas, or possibly burning hydrogen in the future, will keep pollution sources close to where people live. We will either need to electrify the heating of homes and businesses or think much more seriously about how pollution from gas burning can be cleaned up, as we currently do for cars, trucks and buses.”
