What is the air quality in Brussels Central Station / 27 04 2022

Every day more than 60000 people arrive and depart at the Brussels Central Train station. However, only very few people think about the exposure to air pollution at the train stations. Therefore, this weekend the Airscan team performed a study to evaluate the air quality in the central train station of Brussels.

1. Scope Of The Mission

Based on the available scientific publications, it was clear that particulate matter (PM2.5 and PM10) is the main pollutant present indoors. Several studies reported that wind flow generated by the trains as well braking before stations and rapid acceleration after are the main sources of high particulate matter concentration in the train stations. In addition, several studies reported that the pollution levels can be easily affected by the occupation of the train and loading/unloading of luggage.

In this study, the Airscan measurement device with a configuration that includes particulate matter, nitrogen dioxide and volatile organic compounds sensors were used. In addition, the sampling frequency of the device was adjusted to 2 seconds to obtain a high-resolution dataset that should help to explain observed patterns. The device used in this study is shown in the figure below.


Airscan measurement device installed


2. Particulate Matter (PM2.5 & PM10)

As was mentioned in the introduction, particulate matter is the primary pollutant in the train stations. Therefore, Airscan mainly focused on the evaluation of the measured PM trends. The result of the measurement campaign showed that the indoor particulate matter concentration in the central station of Brussels was significantly higher than the recently updated WHO standards. For instance, the average indoor PM10 concentration was 63 µg/m3 while PM2.5 concentration was 41 µg/m3 these values are significantly higher than the limit (5 µg/m3 and 15 µg/m3 for PM2.5 and PM10 respectively). Moreover, the maximum concentration measured was 55 µg/m3 and 87 µg/m3 for PM2.5 and PM10 respectively. The latest articles from the WHO reported that high PM concentration can cause several health problems such as cardiac arrhythmias and heart attacks, and respiratory effects such as asthma attacks and bronchitis. Therefore, it is important to reduce PM concentration in the station to reduce risks of the pollution exposure. The observed trends showed that the trains passing through the station is the main source of pollution. For example, whenever a train approaches the station, the dust concentration starts to increase and reaches its peak half a minute after the train departs from the station (concentration spikes in the first part of the graph below). At the same time, the highest particulate matter concentration was measured in the station at the moment when a high-speed train was passing through the station (17:07). Even though the trains moving through the station result in the concentration jumps, it is important to mention that the background concentration in the station was relatively high (PM10 background was around 55 µg/m3) compared to the outdoor pollution levels (measurements from 17:13 and till the end of the experiment). The graphical overview of the measured PM10 values is given in the figure below.


PM10 concentration measured in the Station

In addition to the measured concentrations, the Airscan team compared the difference in PM fractionation inside the station and outdoors. The results showed that the difference between PM2.5 and PM10 was relatively higher inside the station and was almost neglectable when the device was moved outdoors. The same trend was observed in scientific research performed in the Korean subway network. The author explained the significant dominance of PM10 over PM2.5 particles by the fact that the braking trains mainly generate coarse particles (PM10). The comparison between two PM fractions is given in the figure below.


PM2.5 vs PM10 in the Central Station

3. Nitrogen Dioxide

Oppositely to the particulate matter, the indoor nitrogen dioxide concentration was significantly lower inside the train station than outdoors. The measurement campaign showed that the average concentration of the gas indoors was 7 ppb, while the outdoor concentration was three times higher (21 ppb). The obtained dataset did not show any clear correlation between the movement of the trains through the station and indoor nitrogen dioxide levels. The concentration pattern measured is given in the figure below.


Nitrogen Dioxide concentration measured in the Central Station

4. Light Volatile Organic Compounds

The concentration of light volatile organic compounds inside the station was slightly higher than the levels measured outdoors. However, both average values measured indoors (79 ppb) and outdoors (10 ppb) were well under the threshold limit of 240 ppb. Higher values measured indoors can be explained by the intensive usage of alcohol gels containing ethanol in the station. The measured pattern both inside the station and outdoor is given in the figure below.


Light Volatile Organic Compounds measured in the Central Station

5. Conclusion

The measurement campaign in the central station of Brussels showed high levels of particulate matter (both PM2.5 and PM10). The measured concentrations were significantly higher than the outdoor levels and were way above the recent WHO standards. The trains' movement, braking and acceleration in the station were assumed to be the main contributors to the high particulate matter concentration. On the other hand, the indoor nitrogen dioxide concentration was lower than the outdoor pollution levels. However, both values remained under the threshold limit. At the same time, the measurement campaign did not point to the presence of light volatile organic compounds in the station. Finally, a short term measurement campaign (1 hour) is not always the best representation of the actual pollution levels. Therefore, Airscan will continue measuring the air quality in the Central Station of Brussels to increase the reliability of the results and consequently come up with more solid conclusions.