How bad is the air pollution on the average subway network?

The New York Subway. Image: Getty.

Four more major Indian cities will soon have their own metro lines, the country’s government has announced. On the other side of the Himalayas, Shanghai is building its 14th subway line, set to open in 2020, adding 38.5 km and 32 stations to the world’s largest subway network. And New Yorkers can finally enjoy their Second Avenue Subway line after waiting for almost 100 years for it to arrive.

In Europe alone, commuters in more than 60 cities use rail subways. Internationally, more than 120m people commute by them every day. We count around 4.8m riders per day in London, 5.3m in Paris, 6.8m in Tokyo, 9.7m in Moscow and 10m in Beijing.

Subways are vital for commuting in crowded cities, something that will become more and more important over time – according to a United Nations 2014 report, half of the world’s population is now urban. They can also play a part in reducing outdoor air pollution in large metropolises by helping to reduce motor-vehicle use.

Large amounts of breathable particles (particulate matter, or PM) and nitrogen dioxide (NO2), produced in part by industrial emissions and road traffic, are responsible for shortening the lifespans of city dwellers. Public transportation systems such as subways have thus seemed like a solution to reduce air pollution in the urban environment.

But what is the air like that we breathe underground, on the rail platforms and inside trains?

Mixed air quality

Over the last decade, several pioneering studies have monitored subway air quality across a range of cities in Europe, Asia and the Americas. The database is incomplete, but is growing and is already valuable.

Subway, Tokyo, 2016. Image: Mildiou/Flickr/creative commons.

For example, comparing air quality on subway, bus, tram and walking journeys from the same origin to the same destination in Barcelona, revealed that subway air had higher levels of air pollution than in trams or walking in the street, but slightly lower than those in buses. Similar lower values for subway environments compared to other public transport modes have been demonstrated by studies in Hong Kong, Mexico City, Istanbul and Santiago de Chile.

Of wheels and brakes

Such differences have been attributed to different wheel materials and braking mechanisms, as well as to variations in ventilation and air conditioning systems, but may also relate to differences in measurement campaign protocols and choice of sampling sites.

Second Avenue Subway in the making, New York, 2013. Image: MTA Capital Construction/Rehema Trimiew/Wikimedia Commons.

Key factors influencing subway air pollution will include station depth, date of construction, type of ventilation (natural/air conditioning), types of brakes (electromagnetic or conventional brake pads) and wheels (rubber or steel) used on the trains, train frequency and more recently the presence or absence of platform screen-door systems.

In particular, much subway particulate matter is sourced from moving train parts such as wheels and brake pads, as well as from the steel rails and power-supply materials, making the particles dominantly iron-containing.


To date, there is no clear epidemiological indication of abnormal health effects on underground workers and commuters. New York subway workers have been exposed to such air without significant observed impacts on their health, and no increased risk of lung cancer was found among subway train drivers in the Stockholm subway system.

But a note of caution is struck by the observations of scholars who found that employees working on the platforms of Stockholm underground, where PM concentrations were greatest, tended to have higher levels of risk markers for cardiovascular disease than ticket sellers and train drivers.

The dominantly ferrous particles are mixed with particles from a range of other sources, including rock ballast from the track, biological aerosols (such as bacteria and viruses), and air from the outdoors, and driven through the tunnel system on turbulent air currents generated by the trains themselves and ventilation systems.

Comparing platforms

The most extensive measurement programme on subway platforms to date has been carried out in the Barcelona subway system, where 30 stations with differing designs were studied under the frame of IMPROVE LIFE project with additional support from the AXA Research Fund.

It reveals substantial variations in particle-matter concentrations. The stations with just a single tunnel with one rail track separated from the platform by glass barrier systems showed on average half the concentration of such particles in comparison with conventional stations, which have no barrier between the platform and tracks. The use of air-conditioning has been shown to produce lower particle-matter concentrations inside carriages.

In trains where it is possible to open the windows, such as in Athens, concentrations can be shown generally to increase inside the train when passing through tunnels and more specifically when the train enters the tunnel at high speed.

According to their construction material, you may breath different kind of particles on various platforms worldwide. Image: London Tube/Wikimedia Commons.

Monitoring stations

Although there are no existing legal controls on air quality in the subway environment, research should be moving towards realistic methods of mitigating particle pollution. Our experience in the Barcelona subway system, with its considerable range of different station designs and operating ventilation systems, is that each platform has its own specific atmospheric micro environment.

To design solutions, one will need to take into account local conditions of each station. Only then can researchers assess the influences of pollution generated from moving train parts.

The ConversationSuch research is still growing and will increase as subway operating companies are now more aware about how cleaner air leads directly to better health for city commuters.

Fulvio Amato is a tenured scientist at the Spanish National Research CouncilTeresa Moreno is a tenured scientist at the Institute of Environmental Assessment and Water Research (IDAEA), Spanish Scientific Research Council CSIC.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

As EU funding is lost, “levelling up” needs investment, not just rhetoric

Oh, well. Image: Getty.

Regional inequality was the foundation of Boris Johnson’s election victory and has since become one of the main focuses of his government. However, the enthusiasm of ministers championing the “levelling up” agenda rings hollow when compared with their inertia in preparing a UK replacement for European structural funding. 

Local government, already bearing the brunt of severe funding cuts, relies on European funding to support projects that boost growth in struggling local economies and help people build skills and find secure work. Now that the UK has withdrawn its EU membership, councils’ concerns over how EU funds will be replaced from 2021 are becoming more pronounced.

Johnson’s government has committed to create a domestic structural funding programme, the UK Shared Prosperity Fund (UKSPF), to replace the European Structural and Investment Fund (ESIF). However, other than pledging that UKSPF will “reduce inequalities between communities”, it has offered few details on how funds will be allocated. A public consultation on UKSPF promised by May’s government in 2018 has yet to materialise.

The government’s continued silence on UKSPF is generating a growing sense of unease among councils, especially after the failure of successive governments to prioritise investment in regional development. Indeed, inequalities within the UK have been allowed to grow so much that the UK’s poorest region by EU standards (West Wales & the Valleys) has a GDP of 68 per cent of the average EU GDP, while the UK’s richest region (Inner London) has a GDP of 614 per cent of the EU average – an intra-national disparity that is unique in Europe. If the UK had remained a member of the EU, its number of ‘less developed’ regions in need of most structural funding support would have increased from two to five in 2021-27: South Yorkshire, Tees Valley & Durham and Lincolnshire joining Cornwall & Isles of Scilly and West Wales & the Valley. Ministers have not given guarantees that any region, whether ‘less developed’ or otherwise, will obtain the same amount of funding under UKSPF to which they would have been entitled under ESIF.


The government is reportedly contemplating changing the Treasury’s fiscal rules so public spending favours programmes that reduce regional inequalities as well as provide value for money, but this alone will not rebalance the economy. A shared prosperity fund like UKSPF has the potential to be the master key that unlocks inclusive growth throughout the country, particularly if it involves less bureaucracy than ESIF and aligns funding more effectively with the priorities of local people. 

In NLGN’s Community Commissioning report, we recommended that this funding should be devolved to communities directly to decide local priorities for the investment. By enabling community ownership of design and administration, the UK government would create an innovative domestic structural funding scheme that promotes inclusion in its process as well as its outcomes.

NLGN’s latest report, Cultivating Local Inclusive Growth: In Practice, highlights the range of policy levers and resources that councils can use to promote inclusive growth in their area. It demonstrates that, through collaboration with communities and cross-sector partners, councils are already doing sterling work to enhance economic and social inclusion. Their efforts could be further enhanced with a fund that learns lessons from ESIF’s successes and flaws: a UKSPF that is easier to access, designed and delivered by local communities, properly funded, and specifically targeted at promoting social and economic inclusion in regions that need it most. “Getting Brexit done” was meant to free up the government’s time to focus once more on pressing domestic priorities. “Getting inclusive growth done” should be at the top of any new to-do list.

Charlotte Morgan is senior researcher at the New Local Government Network.