A major monitoring programme, the first of its kind anywhere in the world, has systematically measured air quality at more than 100 mainline stations across the country and the results are now driving action.
The Air Quality Monitoring Network (AQMN), established by the Rail Safety and Standards Board (RSSB) with funding from the Department for Transport (DfT), has been collecting data on nitrogen dioxide (NO₂) and particulate matter (PM₁₀ and PM₂.₅) at stations since 2022. The goal being to find out where pollution levels are highest, and do something about it.
Rail is already one of the lowest-emission transport modes, contributing just 4% of domestic transport NOx pollution, with emissions falling by nearly 40% in the decade to 2023. But national averages don’t tell the full story. In enclosed or partially enclosed stations where diesel trains operate, emissions can accumulate, creating localised hotspots that passengers and staff breathe in every day.
The AQMN was designed to identify such hotspots. Using a combination of diffusion tubes for long-term average readings, plus reference monitors and low-cost sensors at selected sites, the network has built a detailed picture of air quality at stations from Birmingham New Street to Inverness.
What the data shows is that at most stations, air quality is generally good but at around 50 locations, annual mean NO₂ concentrations exceeded 40 μg/m³, a benchmark aligned with the UK’s outdoor air quality objective.
At Birmingham New Street, which sits underneath a shopping centre in an enclosed underground environment, levels were particularly high. In 2023, one location on Platform 10 recorded an annual mean of 327.8 µg/m³, with hourly peaks reaching 2,236 µg/m³.
In fairness, such levels are atypical, the result of a perfect storm involving high numbers of diesel trains, idling engines and poor ventilation in an enclosed space.
On the back of this study, train operators and Network Rail have developed Air Quality Improvement Plans (AQIPs) for stations where monitoring shows a need for action. These plans set out measures ranging from operational changes to long-term investment in cleaner technology.
Some measures are already in place. CrossCountry has introduced a revised engine shutdown policy, cutting permitted idling times from 15 minutes to five at selected locations, and is rolling out Intelligent Engine Stop Start technology across its fleet. Chiltern Railways is reviewing idling processes and considering location-specific changes. West Midlands Trains has established idling focus groups at Birmingham New Street and Hull, bringing together operators and station managers to find practical, site-specific solutions.
Longer-term, the shift to cleaner traction is accelerating. East Midlands Railway is introducing new bi-mode trains on the Midland Mainline, which will run on electric power where available and use cleaner diesel engines elsewhere. TransPennine Express has trialled tri-mode technology, allowing zero-emission operation when entering or leaving stations. Grand Central plans to introduce tri-mode trains into service by 2028.
Infrastructure improvements are also being trialled. At Birmingham New Street, ventilation upgrades were implemented in 2018, and a Pluvo air filtration column was installed on Platform 10/11 in January 2024. Salisbury station began a six-month trial of similar technology in December 2023. South Western Railway is phasing out gas boilers and working with Network Rail on anti-idling signage to reduce emissions from taxis and staff vehicles.
The DfT has now published a new Rail Air Quality Policy Statement, setting out a framework for managing and improving air quality across the passenger network in England. It establishes three clear outcomes: reduce emissions from trains, strengthen air quality management at stations, and improve understanding of rail air quality.
To support this, the government is investing £1 million to extend the AQMN until at least 2030, providing a long-term evidence base to track progress. RSSB is also developing a public data portal to make air quality information openly accessible, alongside plain-language summaries for non-experts.
New research is also underway. A follow-up study to Imperial College London’s 2021 onboard air quality measurements will revisit trains where mitigation measures have been introduced, to assess whether NO₂ and particulate levels have improved. Handheld monitoring devices are being trialled to support future data collection.
Rachael Everard, RSSB’s Director of Sustainable Development, said: ‘Air quality matters; the air we breathe is important to our health and wellbeing and to passenger comfort. As an industry, we are committed to creating a railway that has a positive impact on local air quality.
‘Our research is helping identify the minority of areas where air quality is an issue on our network. By proactively identifying these locations, rail can act and target improvements quickly. Out of more than 2,500 stations nationwide, 50 needed an air quality improvement plan, and operators are already putting those into practice.’
Photo: Lx1
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