Nitrogen Dioxide (NO2) is a harmful pollutant formed mainly from the burning of fossil fuels in vehicles and industrial processes. It can harm our lungs through inflaming airways and worsen respiratory conditions such as asthma. The ten district councils that represent the Greater Manchester Combined Authority are directed by the government to reduce roadside levels of NO2 to an annual mean level of 40 µg/m³ by no later than 2026 (this is laid out in the Environment Act 1995 (Greater Manchester) Air Quality Direction 2025). They have set out how they will achieve this in their GM Clean Air Plan (CAP) Their plan is based on a number of investment-led measures, predominently based on transitioning buses and taxis towards electric vehicles (rather than reducing car journeys or increasing active travel):
- £51.1m in 40 new zero-emission electric buses depot electrification in Manchester & Bolton and 77 OEM Euro VI buses
- £30.5m for a Clean Taxi Fund to support GM-licensed owners to upgrade to cleaner vehicles
- £5m to manage traffic flows on roads in Manchester and Salford
Every year, GMCA measure annual mean levels of NO2 (in µg/m3) at key sites across Greater Manchester and, in June/July each year, publish the results of previous year’s measurements on their GM Clean Air Data Hub. These levels are used to monitor progress towards achieving the levels set out in the GM CAP. The latest report to the GM Air Quality Administration Committee in July 2025 shows that there were 38 locations (around 15%) in exceedance of 40 µg/m3 in 2024.
The number of diffusion tubes changes each year and readings are not always successful, so it’s not always easy to see progress. We have used the diffusion tube data to represent how levels of NO2 have changed between 2023 and 2024. It should be noted that, of the 270 locations used to monitor levels for the CAP in 2024, only 265 provided data for both these years. The graph below shows annual mean levels of NO2 in (in µg/m3) and by how much they have gone up or down between 2023 and 2024.
Click here for an interactive version of this graph.
The red dashed line shows the target average mean level of 40 µg/m³ NO₂ (although it should be noted that in the GM CAP only anything over 40.4µg/m3 will be considered an exceedance and below 40.4µg/m3 will be rounded down to 40µg/m3). Around 15% of sites monitored are over this threshold in 2024. In the interactive version of the graph, the specific location of each tube can be found by selecting the relevant dot. These locations can also be seen on the diffusion data map on the GM Clean Air Data Hub.
It is worth noting that, since 2021, the World Health Organisation (WHO) air quality guidelines recommends an annual mean level of 10 µg/m3.
Whilst there are generally improvements, with 91% of sites monitored showing a decrease in levels from 2023 to 2024, none of the recorded annual mean levels meet the WHO target (with the lowest level being 18µg/m3). It is also concerning that some locations (those shown as Most Concerning in the graph) that are already measuing over 40 µg/m3 are still showing a year on year increase. For example, the measurement for the tube on Lever St in the city centre is 59.4 µg/m3 and increasing.
Finally, there is no way of linking the key compliance site locations set out in the GM CAP with the diffusion tube data, as a different naming convention is used. This means that it is not possible to see progress against the target values for 2026. We will not have clarity on the figures for 2026 until the final report is issued in June 2027.
Our ask is therefore:
- Greater transparency on year on year progress against the targets for key compliance sites (including alignment of naming convention)
- More detail on specific measures for improvement for those locations represented in the graph as most concerning or needing observation
- An outline plan of how GMCA will move from the current target of 40 µg/m3 to the WHO recommended interim target level of 20 µg/m3
- Stronger measures to disincentive short car journeys and increase sustainable or active travel