---
title: "Air quality in public transport: no longer an option to restore confidence"
url: "https://www.systra.com/en/expert_insights/air-quality-in-public-transport-no-longer-an-option-to-restore-confidence/"
type: expert_insights
date_published: 2020-12-11
date_modified: 2024-06-26
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language: en-US
word_count: 1639
reading_time: 9 min
canonical: "https://www.systra.com/en/expert_insights/air-quality-in-public-transport-no-longer-an-option-to-restore-confidence/"
featured_image: "https://www.systra.com/wp-content/uploads/2020/12/gettyimages-1272679625-1.jpg"
type-insight:
  - Innovation
---

# Air quality in public transport: no longer an option to restore confidence

![Air quality in public transport: no longer an option to restore confidence](https://www.systra.com/wp-content/uploads/2020/12/gettyimages-1272679625-1.jpg)

**Air quality is a structural problem, which did not appear with Covid-19. On the other hand, the health crisis has put it back at the centre of users’ concerns. They have turned away from public transport in favour of individual transport. There is a strong desire on the part of operators and transport authorities to provide solutions and restore confidence, which is essential if passengers are to use public transport again. What are the solutions to improve air quality? How can the most appropriate one be chosen for each situation? Our experts provide some answers. **

Air quality is one of the most pressing issues of the 21^(st) century.
Throughout the world, people suffer from serious diseases as a result of poor
air quality in cities due to the development of ground transport and the
increasing impact of residential heating and industrial activities. Air
pollution contributes to around 7 million premature deaths annually worldwide
(11.6% of all global deaths) including 630,000 in Europe. Big cities are the
worst affected by the high level of air pollution and the annual costs of
premature mortality^([1]).

Nowhere are people effectively protected from pollution and public transport is
not an exception. Pollution from outside (the city) and produced by circulation
of the rolling stock itself, fills metro stations, tunnels and trains. With
ground transport, travellers and operators’ employees are constantly exposed to
traffic pollution.

Recent air quality measurements undertaken in metro stations around the world
have shown that pollution considerably exceeds WHO (World Health Organization)
recommended levels, especially in the case of the concentration of particle
matter PM2.5. Considering that many passengers spend 60 to 90 minutes a day on
public transport during their working lives, the impact of air pollution here
can no longer be ignored. In the case of high speed and regional trains,
passengers spend 2 to 6 hours on board per trip so ensuring good air quality
remains an of paramount importance.

The current global health crisis related to Covid-19 has changed the
transportation priorities of populations, with a decline in trust for public
transport and a shift towards individual transport modes. Regular disinfection
and social distancing measures are essential if the population is to feel safe
again^(2). But these measures are insufficient.

## A systemic approach, not limited to rolling stock

Air quality and cleanliness of surfaces are major issues in restoring confidence
in public transport and speeding up a return to normal operations. The question
of air quality should be approached with all aspects of the transport system in
mind, including the rolling stock and the infrastructures.

- **In urban and suburban areas**, passengers spend relatively short periods in
  transport, usually crowded, that increase the risk of contact with potentially
  infected surfaces (handrails and seats) and proximity to other passengers. The
  air circulated by the ventilation and/or conditioning devices contributes to
  spreading pollution and viruses, but the risk is low because of distance from
  the air source. On the other hand, for drivers and other personnel, who spend
  hours on board, air conditioning systems must aim at significantly reducing
  the mixing of bacteria and viruses.

- **In suburban and interurban areas**, the health risks are relatively high
  because of air recirculation by the air conditioning system and long-lasting
  contacts with potentially infected surfaces (seats, tables) and toilets.

- **For infrastructure**, all locations and access controls, including payment
  terminals, should be considered too.

## How can the most effective air treatment solutions be chosen?

In order to propose the most suitable solution for each situation, we propose a
three-step process.

### Step 1: acquire extended knowledge and understanding of the current situation

Establishing the current situation on-board, with the rolling stock, or within
the stations goes through a reverse engineering analysis: How has it been built
or manufactured? Why have certain constructive and air treatment solutions been
chosen? What could be modified at low cost? What cannot be modified?

- **Transport system environment**

Concerning metro infrastructure, for each case, SYSTRA will build an air
circulation profile of the station using  CFD (Computational Fluid Dynamics)
modelling software to define how the air flows from/to the tunnel, through the
exhaust shafts and through the station accesses, at platform level.

The analysis of the current on-board and rolling stock situation  involves
understanding of the air treatment solution implemented at the HVAC (Heating,
Ventilation, Air Conditioning) (or simply ventilation) level, the quality of the
doors and windows sealing, the frequency of the stops and doors opening, the
train’s interior design and the air circulation ensured by the HVAC or
ventilation.

- **Nature, source and quantity of air pollutants**

The data collected by the operator are then classified in terms of occurrence,
nature, quantity and toxicity. This then enables the appropriate measurement
campaigns to be specified and the figures analysed after collection.

SYSTRA has an overall view of the risks prevailing in the environment of the
different modes of transport and these are summarised in Table 1 and Table 2
below.

![air-quality-1](https://www.systra.com/wp-content/uploads/2020/12/air-quality-1.jpg)

_Comparison of air quality in different modes of transport.Sources: Pollution atmosphérique n°215 – July-September 2012, Assessment of the exposure of city dwellers to air pollutants during their journeys in the Paris conurbation ; EASA, 2014, “Preliminary cabin air quality measurement campaign”._

| 󠀁**Pollutant**󠁿 | 󠀁**Pollutant nature**󠁿 |
| --- | --- |
| 󠀁**PM10**󠁿 󠀁**PM2.5**󠁿 | 󠀁**Primary particles: **󠁿mixture of different chemical compounds from road traffic, residential sector, construction sites, agriculture. 󠀁**Secondary particles:**󠁿 NO󠀁_(2)󠁿, SO󠀁_(2)󠁿, NH󠀁_(3)󠁿, VOC react with each other, suspension of soil dust. |
| 󠀁**NO󠀁_(2)󠁿**󠁿 | Incomplete combustion (road traffic and residential heating). Forms naturally in the atmosphere from NO and O󠀁_(3)󠁿. |
| 󠀁**CO󠀁_(2)󠁿**󠁿 | Source linked to human activity: combustion of fossil fuels. Natural source: respiration and decomposition |
| 󠀁**CO**󠁿 | Incomplete combustion (road traffic and residential heating) |
| 󠀁**VOC (volatile organic compounds)**󠁿 | Wide range of products from: petrol refining, combustion, use of paint and cleaning products, coating. |

_Principal sources of the air pollution in public transport. Source: https://www.airparif.asso.fr/_

### Step 2: simulate various air treatment solutions

Improving the air quality in a metro station or in a train can be achieved
thanks to the combination of various devices, equipment and structural changes.

In addition to our thorough understanding of ventilation policy on metro
stations linked to international standards (NFPA 130) and regulations in ‘ERP’
(establishments receiving the public) in France, for example, SYSTRA maintains a
regular benchmark on industrial air treatment solutions and will offer a
customised set of recommendations in each case.

These recommendations will concern infrastructure design that can have an impact
on the air quality (platforms, access, equipment rooms, tunnels etc.). The
impact of platform screen doors on the air flow, temperature management and
smoke control are very well understood at SYSTRA and will feed the feasibility
studies.

Thanks to a comprehensive understanding of the origins of the various pollutants
present in public transport areas and prior to any technical treatment of the
air, SYSTRA will recommend limiting the emissions at their source, as far as
possible.

Finally, as far as possible, it is preferable to limit emissions at source.
Transport systems produce them, especially through mechanical braking, tyre wear
on the rails for pneumatic metros, friction on the rails, infrastructure
degradation (ballast, concrete track), diesel vehicle emissions, etc. To reduce
them at the outset, solutions exist, and industrialists and equipment
manufacturers are currently developing innovative ones.  All sources of
pollutants that cannot be avoided should be treated afterwards.

There are several air treatment solutions on the market today, and others are
under development. The challenge lies in selecting the most appropriate air
filtration equipment according to the assessed risks. A combination of several
solutions may be necessary, as shown in the figure below.

![qualite-de-lair-2](https://www.systra.com/wp-content/uploads/2020/12/qualite-de-lair-2-1024x450.jpg)

### 󠀁**Step 3: evaluate the technical solution pe**󠁿r󠀁**formance**󠁿

After having selected solutions involving architectural and structural changes
if necessary, and the industrial air treatment devices, SYSTRA will validate the
proposed solutions by means of simulation.

SYSTRA offers its clients a portfolio of services to assist them in creating
solutions, from design to implementation:

- Supporting the operator in **planning the implementation phases **with respect
  to the Operational and Maintenance constraints of the transport system.
- **Preparing the technical requirements** of the structural changes and of the
  equipment to acquire and install with a focus on RAM+S (Reliability,
  Availability, Maintainability+ Safety) factors of the new equipment and on the
  overall performance of the modified station or train.
- **Consolidating a preliminary cost estimate **of the air quality improvement
  project and assist the operator in the selection of the proposed solutions.
- After a building and testing phase of the project,
  **follow up of the air quality improvement** in the short and mid-term.

##  In conclusion

We are involved in creating more sustainable, safer and more accessible
mobility. We offer a system approach aimed at solving the air quality problem in
a public transport network and restoring the confidence of passengers.

Restoring this confidence in transport networks is a major challenge for public
transport if it is to remain the backbone of tomorrow’s sustainable cities.

We are ready to meet the specific challenges of its clients and create with them
the clean transport of tomorrow, from the original design or the assessment
stage, until the testing & commissioning of a transport system considered at its
full extent as a healthy environment.

Even if we all wish that the Covid-19 issue will soon be over, the awareness
that it has generated should start a strong and sustainable momentum towards
improving air quality in transport networks.

---

[[1]](https://www.systra.com/en/expert_insights/air-quality-in-public-transport-no-longer-an-option-to-restore-confidence/#_ftnref1)
European Public Health Alliance: “How much is air pollution costing our
health?”, August 2020.

[[2]](https://www.systra.com/en/expert_insights/air-quality-in-public-transport-no-longer-an-option-to-restore-confidence/#_ftnref2)
McKinsey study: “Transportation during the pandemic: what is considered safe?”,
September 2020.