Air quality has become an increasingly prominent issue across the rail industry in recent years and, while rail remains one of the most environmentally sustainable modes of transport at a national level, new evidence shows that the experience at station level can tell a more complex story.
The latest findings from the Rail Safety and Standards Board’s (RSSB) Air Quality Monitoring Network (AQMN) offer a comprehensive picture of pollutant concentrations across Britain’s rail estate, and the conclusions are nuanced. The study, which covers the period covering 2022 and 2023, shows that air quality is within acceptable bounds for the majority of stations, but it also finds that conditions are less reassuring at a significant minority of locations, sometimes markedly so. It should be noted that the data cannot be used to measure air quality for those working in stations, as worker exposure is assessed differently under separate legal requirements.
Under the microscope
The AQMN was commissioned by the Department for Transport (DfT) in 2020 and delivered by RSSB to address a long-standing gap in knowledge about air quality within railway stations. Historically, data on air quality within stations has been limited, often focused on individual locations rather than the network as a whole. The AQMN was therefore established with the objectives of:
- Providing a clear picture of air pollution levels across stations in Great Britain.
- Identifying locations where air quality improvements may be required.
- Assessing the effectiveness of mitigation measures.
- Improving transparency and public understanding of air quality in railway environments.
- Supporting evidence-based decision making across the industry.
By 2022, monitoring equipment had been deployed across more than 100 stations, targeting those most likely to experience elevated pollution levels. These were typically stations which exhibited several risk factors including: high volumes of diesel services; enclosed or covered station layouts that restrict air circulation; the presence of sidings where trains may idle; and stations located in areas already affected by poor air quality.
In 2023, the network was refined to focus on 71 locations, while additional sites were added where potential risks had been identified.
The AQMN focused on the three pollutants most relevant to railway environments. The first of these is Nitrogen dioxide (NO₂), which is produced primarily by combustion engines, including diesel trains and road vehicles associated with station activity. Second and third are particulate matter – PM10 and PM2.5 – which are tiny airborne particles created through combustion, mechanical wear from wheels and brakes, and the re-suspension of dust by moving trains.
These pollutants are widely recognised as important indicators of air quality and are linked to respiratory and cardiovascular health impacts when exposure occurs over prolonged periods.
Findings
The findings gathered by the AQMN show that most stations perform reasonably well. In 2022, the majority recorded nitrogen dioxide (NO₂) concentrations below 40 μg/m3. This is the threshold used as an improvement indicator and the ambient air quality objective used by local authorities (though currently there is no legal or contractual requirement for stations to achieve this). However, 35 stations exceeded this level and by 2023, that number had risen to 47.
The highest concentrations were typically recorded on platforms, where trains are present and emissions are most concentrated. By contrast, the lowest levels were usually found in external areas away from railway operations. Enclosed stations and those with significant canopy coverage were more likely to experience higher pollution levels due to reduced air circulation.
One of the most notable findings was recorded at Birmingham New Street, where, in 2023, the highest annual average nitrogen dioxide concentration network reached 327.8 µg/m³ in specific areas. Short-term spikes were also recorded when diesel trains were present or idling, demonstrating how operational activity can influence air quality in real time.
At first glance, the findings might suggest a worsening picture, but in reality, the upward shift reflects a more targeted approach to monitoring. Lower-risk stations were removed from the network, while additional higher-risk locations were brought in. The data, therefore, provides a clearer view of where the real challenges lie.
One of the study’s most consistent findings is the variation in air quality within stations themselves, highlighting that not all spaces are equal. Platforms emerge as the most problematic areas, regularly recording the highest pollutant concentrations. This is perhaps unsurprising. They are closest to the primary source of emissions – trains themselves, particularly those powered by diesel engines.
By contrast, concourses and waiting areas generally show lower levels, while outdoor ‘background’ locations away from railway activity tend to record the lowest concentrations. Even so, enclosed concourses can still experience elevated pollution where ventilation is limited.
Footbridges and subways present another interesting case. Positioned above or below platform level, these areas can act as pockets where pollutants accumulate, especially in stations with restricted airflow.
Thus, the message is that air quality within stations is highly spatial, and passenger exposure can vary significantly depending on where they spend their time.
Diesel dominance
At the heart of the issue is diesel traction, and the study leaves little ambiguity here. Diesel trains, particularly when idling, are the dominant contributor to poor air quality in stations.
High-resolution monitoring shows a direct relationship between train activity and pollutant levels, and this is not a problem limited to outdated rolling stock. Peaks in nitrogen dioxide and particulate matter align closely with the presence of diesel trains, especially when engines are left running in enclosed or semi-enclosed environments.
While operational requirements mean that some level of idling is unavoidable, whether for safety checks, system readiness, or timetable resilience, the cumulative effect is significant.
The challenge, therefore, is twofold: reliance on diesel traction must be reduced over the long term, while operational practices must be addressed in the here and now.
Hotspots and extremes
While averages across the network are relatively moderate, they can mask extreme localised conditions, the study found.
Birmingham New Street stands out as a notable example. The station recorded the highest annual mean NO₂ concentration in the network, alongside exceptionally high short-term peaks. Such spikes are not constant, and they do not represent conditions across the entire network. However, they do highlight the potential for significant exposure in specific environments, particularly for frequent users.
These hotspots tend to share common characteristics: enclosed designs, high traffic volumes, and a continued reliance on diesel services. They are, in many ways, a legacy of earlier railway design meeting modern environmental expectations.
It is important, however, to place these findings in context. At a national level, rail contributes only a small fraction of the UK’s total air pollutant emissions and compared to road transport, its impact is relatively minor. Unfortunately, this big-picture perspective does not negate the local experience.
Air quality is, by its nature, a localised issue. Even low-emission sectors can produce high concentrations in confined or poorly ventilated environments, and for passengers there is little distinction. What matters to them is the quality of the air they breathe on the platform, not the sector’s share of national emissions.
Tackling the challenge
Encouragingly, the study highlights a range of actions already underway across the industry.
Electrification remains the most effective long-term solution, removing diesel emissions at source. Alongside this, newer rolling stock is helping to reduce pollutant output, even where diesel operation continues.
Operational changes are also playing a role. Efforts to reduce unnecessary idling – through revised procedures, improved driver awareness, and technological solutions – are beginning to show promise, although progress is uneven and context-dependent.
Crucially, the introduction of Air Quality Improvement Plans (AQIPs) marks a more structured approach. Stations exceeding the improvement indicator are now required to develop targeted strategies, setting out practical measures to reduce emissions and improve conditions.
These plans recognise that there is no one-size-fits-all solution. Each station presents its own combination of challenges, requiring tailored interventions and, often, collaboration between multiple stakeholders.
Beyond operations and rolling stock, station design itself plays a critical role. The study reinforces a longstanding principle: ventilation matters. Open-air stations naturally allow pollutants to disperse, reducing concentrations even where emissions are relatively high. Enclosed or covered stations, by contrast, can trap pollutants, leading to build-up over time.
This raises important questions for future infrastructure projects. As the industry continues to invest in major stations and upgrades, air quality considerations will need to be embedded from the outset, rather than addressed with hindsight.
Rail’s legacy estate presents a more complex challenge, as retrofitting improved ventilation or redesigning enclosed spaces is rarely straightforward, particularly in historic or constrained locations. Nevertheless, incremental improvements, whether through airflow management, operational changes, or technology, can still make a difference.
A measured outlook
So what, ultimately, does the study tell us?
First is that air quality at stations is not a universal problem, but neither is it an insignificant one. The majority of locations perform well, but a significant minority require attention.
Second, the issue is highly localised. Conditions vary not just between stations, but within them, influenced by design, operations, and the presence of diesel traction.
Finally, and more positively, it tells us that the industry is not standing still. Monitoring has improved dramatically, mitigation measures are in place, and longer-term strategies are moving in the right direction.
Perhaps most importantly, the AQMN underscores the value of visibility. By quantifying the problem, the study has shifted air quality from an abstract concern to a measurable, manageable challenge. For an industry built on precision and performance, that is a significant step forward.
The task now is to translate this insight into impact and ensure that the railway not only moves people efficiently, but does so in an environment that supports the health and wellbeing of everyone who uses it
Image credit: iStockphoto.com
