London’s ULEZ reduced the city’s nitrogen dioxide levels by a few percent during the first few weeks of implementation.
This is according to a study by Imperial College London researchers, who say their findings highlight that ULEZs are not a silver ball and that sustained improvements in air pollution require more action.
Between 2016 and 2020, the number of Londoners living in areas with illegally high levels of nitrogen dioxide fell by 94 per cent, and in parallel with this, there were other reductions in London’s air pollution. New research from Imperial has found that changes in air pollution around the introduction of ULEZ in April 2019 were small compared to these long-term improvements.
The researchers used publicly available air quality data to measure changes in pollution in the twelve-week period from 25 February 2019, before ULEZ was introduced, to 20 May 2019, after it had been implemented. They checked for the effects of weather variations and then used statistical analysis to look for and quantify changes in pollution.
The case of London shows us that [ULEZ] works best when combined with a broader set of policies that reduce emissions across sectors such as retrofitting bus and taxi, support for active and public transport and other polluting vehicle policies Dr. Marc Stettler Department of Civil and Environmental Engineering
The researchers behind the study, published in Environmental research letters, says it emphasizes the importance of combining a broad set of effective clean air measures that could include local initiatives such as reducing transport emissions and the use of stoves and regional policies that reduce, for example, agricultural emissions. This is particularly important for cities considering a ULEZ, and it comes as London’s ULEZ was expanded to create a larger zone in October 2021.
Corresponding author of the research Dr. Marc Stettler, from Imperial’s Department of Civil and Environmental Engineering and Center for Transport Studies, said: “Our research suggests that a ULEZ in itself is not an effective strategy to improve air quality – the case of London shows us that it works best when combined with a broader set of policies that reduce cross-sectoral emissions such as retrofitting of buses and taxis, support for active and public transport and other polluting vehicle policies. “
Air pollution caused 40,000 deaths in the UK in 2019 – around 4,000 of them were in Greater London. Worldwide, outdoor air pollution accounts for about 4.2 million deaths a year due to conditions such as stroke, heart disease, lung cancer and acute and chronic respiratory diseases.
In April 2019, the Mayor of London introduced ULEZ, an area where drivers of more polluting vehicles must pay a daily fee, with the aim of reducing air pollution emissions from road transport and speeding up compliance with EU air quality standards. ULEZ is one of several London air pollution policies introduced since 2016, such as the Low Emission Zone, Low Emission Bus Zones and bus and taxi electrification.
To conduct the study, the researchers analyzed air quality data from roadside and non-roadside air quality monitors across London, and compared data over a twelve-week period from before and after ULEZ was introduced.
They found that compared to the overall decline in London’s air pollution levels, ULEZ caused only small improvements in air quality in the weeks after the start date: an average reduction of less than 3 percent for nitrogen dioxide concentrations and negligible effects on ozone and particulate matter concentrations (PM2.5).
They also found that the biggest improvements to air quality in London actually took place before ULEZ was introduced in 2019.
Cities considering air pollution policies should not expect ULEZs to solve the problem alone, as they contribute only marginally to cleaner air. Dr. Marc Stettler Department of Civil and Environmental Engineering
They detected changes in the levels of nitrogen dioxide and ozone at 70 percent and 24 percent of the monitoring sites, respectively, around the time ULEZ was introduced. Among these sites, changes in air pollution varied quite significantly, and in some places pollution actually worsened, with relative changes ranging from -9 percent to 6 percent for nitrogen dioxide, -5 percent to 4 percent for ozone, and -6 percent to 4 percent for PM2. 5.
The researchers suggest that other cities that are considering implementing these schemes should only consider them along with a combination of other measures. Dr. Stettler said: “Cities considering air pollution policies should not expect ULEZs to solve the problem alone, as they contribute only marginally to cleaner air. This is especially true for pollutants that may originate elsewhere and be blown into the city. of winds, such as particulate matter and ozone. “
“Since the introduction of London ULEZ, similar schemes have been introduced in Bath, Birmingham and Glasgow, but on a much smaller scale. Several other cities have plans to implement clean air zones and our results can contribute to the development of their policies.”
“Has the Ultra Low Emission Zone in London improved air quality?” by Liang Ma, Daniel J. Graham and Marc EJ Stettler, published November 16, 2021 in Environmental research letters.
See the press release in this article