Whether it is a bus, metro, tram or train, millions of people use public transport every day.
This prolonged time spent in enclosed spaces highlights the importance of adequate indoor air quality, as it is not only the comfort of passengers that is at stake, but also their health: high levels of pollutants such as CO2, suspended particles and other pollutants such as volatile organic compounds from perfumes or deodorants can have a negative impact on passengers’ wellbeing when concentrated in enclosed spaces.
Why is it important to monitor indoor air quality in public transport?
As several studies on public transport have shown, during urban travel, these vehicles accumulate a number of pollutants directly from outdoor pollution from road traffic and from the occupants themselves. The main pollutants affecting indoor air quality are
- Fine particles in their various sizes such as PM10 and PM 2.5, which come from brakes, rail wear and dust and mainly affect the lungs and the cardiovascular system.
- Carbon dioxide (CO2) and carbon monoxide (CO), produced by passengers and traffic, increase significantly during peak hours and cause fatigue and discomfort at high levels.
- Volatile organic compounds (VOCs) produced by the occupants themselves, from perfumes and colognes, deodorants and cosmetics.
- Biological contaminants such as viruses and bacteria, as poor air quality facilitates the transmission of pathogens through particulate matter, posing a risk to both passengers and staff.
Air quality studies in public transport
The BUSAIR project in Barcelona monitored air quality inside its city buses and found that peaks in PM2.5 and black carbon concentrations coincided with the points of highest pollution in the city (traffic jams, tunnels…), highlighting the importance of adequate ventilation to mitigate the negative effects of outdoor pollution.
In Istanbul, Turkey, another recent study carried out on intercity buses showed that on long routes, CO2 levels can vary dramatically depending on the number of passengers and the frequency of door openings. In these cases, CO2 levels reached over 3000 ppm on routes with inadequate ventilation, exceeding the limits recommended by organisations such as WHO and ASHRAE. High CO2 levels not only indicate poor ventilation, but can also cause symptoms such as fatigue, headaches and lack of concentration, which can affect both passengers and drivers.
In Wellington, New Zealand, a pilot study was conducted in 2022-2023 to measure CO2 levels in public buses.
During the study, elevated CO2 levels were observed on 22% of the trips monitored, indicating inadequate ventilation; in fact, double-decker electric buses showed a higher risk of CO2 accumulation on the upper deck due to the lack of adequate ventilation mechanisms.
The Anses project in France analysed the toxicity of suspended particulate matter in metro and underground stations and carriages and found that particulate matter levels in these spaces were three times higher than in urban outdoor areas, mainly due to worn railway materials.
The study recommends air quality indicators, proposes maximum levels of particulate matter that should not be exceeded, and calls for improvements in ventilation and emission reduction, including real-time air quality monitoring.
It is important to note that poor indoor air quality is not only related to pollutants, but also to environmental parameters such as temperature and humidity, which have a direct impact on passenger comfort during travel.
Benefits of monitoring air quality in public transport
By using IoT air quality sensors and monitors, dangerous levels of CO2, particulate matter and other pollutants can be detected before they reach critical levels, allowing corrective action to be taken for proper ventilation. This has a direct impact on improving public health, as reducing exposure to these pollutants reduces the risk of respiratory and cardiovascular disease.
Monitoring systems also help improve energy efficiency, as an intelligent ventilation system can automatically adjust airflow as needed, avoiding excessive or inefficient ventilation.
Nanoenvi IAQ, the indoor air quality solution for public transport
The Nanoenvi IAQ device is specifically designed to monitor indoor air quality in enclosed spaces such as buses, subways and trains.
It is a multi-sensor device that incorporates a wide range of sensors to measure key pollutants such as CO2, PM1, 2.5, 4 and 10 particles, VOCs, as well as temperature and relative humidity in real time, providing a complete picture of indoor air quality.
Thanks to IoT technology, the data collected by Nanoenvi IAQ is transmitted in real time to a cloud-based data visualisation platform, enabling continuous monitoring from any location.
If elevated levels of pollutants are detected, the system can send immediate alerts, enabling rapid intervention to improve air conditions.
Unlike other devices that require complex installations, Nanoenvi IAQ is compact and easy to install and maintain, minimising operating costs.
