What is the air quality in Brussels Central Station May 2022 / 31 05 2022

In April 2022 Airscan launched an independent case study around air quality assessment in the Central Train Station of Brussels to evaluate potential health impacts. In the first report (April 2022) the Airscan team already reported about high PM values measured indoors and about the importance of air quality in such facilities as enclosed train stations because of a high number of people arriving and departing from the station. In this article, Airscan will continue to share the observations and concentrations measured in Brussels Central train station in May 2022.

1. Particulate matter

The measurement campaign performed in May 2022 discovered high particulate matter concentration in the station. Both the average concentrations of PM2.5 and PM10 were above the threshold limit developed by WHO (2005) with the values of 41 µg/m3and 63 µg/m3 respectively. The measurement campaign performed in May showed a slightly lower concentration. For instance, the average PM2.5 concentration measured in May 2022 was 28 µg/m3 while the average PM10 concentration was 46 µg/m3. Even though the detected average concentrations in May 2022 were lower, the hypothesis that trains’ acceleration and braking generate dust particles was confirmed. For instance, in the period from 16:12 till 16:27 3 trains stopped and departed from the platform which resulted in 3 corresponding PM peaks (figure 1). Moreover, the observed pattern showed 3 periods when dust concentration was low (at 16:35, 17:22 and 17:52). At these time intervals, speed trains were passing through the platform line located 15 meters from the sampling location. Therefore, it was concluded that the wind turbulence created by a passing train can cause a short term flash out of dust particles and subsequently concentration drop. On the other hand, it is important to mention that the pollution levels increased immediately after the speed train left the station.

1

Figure 1. PM2.5 concentration profile measured in the Station

The 2nd measurement campaign also showed that the dust particles fractionation in the train station is different from a typical indoor environment (office/house). The comparison of PM10 and PM2.5 concentrations measured in the train station is given in the figure below. The figure shows that the concentration difference between PM10 and PM2.5 during the measurement campaign was relatively high and was more than 35 µg/m3 at a certain period of the test (Figure 2). Moreover, the measurement campaign detected several intervals when PM10 concentration was increasing while PM2.5 concentration was decreasing. The observed trends were explained by J. Wang et al. who performed an identical study in Shangai, China. The scientist reported that the opening of the trains’ doors and wind turbulence generated create favorable conditions for coarse particles formation.

2

Figure 2. Comparison of PM2.5 and PM10 measured

2. Nitrogen dioxide.

In April 2022 Airscan reported that the indoor nitrogen dioxide levels (the average concentration was 13 µg/m3) within the train station were under the threshold limit of 25 µg/m3. The new measurement campaign performed in May showed identical values and the average concentration during 2 hours campaign was 12.5 µg/m3. Also during the measurement campaign, 3 rapid NO2 concentration growth was observed at 16:35, 17:22 and 17:52, moments when speed trains were passing through the station and bringing the pollution from the outdoors to the indoor environment (Figure 3).

3

Figure 3. Nitrogen dioxide gas concentration profile measured in the Station

3. Comparison of indoor and outdoor air quality

In addition to the indoor air quality measurements, an outdoor monitoring device was installed in front of the train station. This approach helped to evaluate and compare indoor and ambient pollution levels. The analysis showed that the dust particles' concentration inside the station was significantly higher compared to the outdoor levels. For example, the average outdoor concentration during the measurement period was 8.5 µg/m3 while the indoor concentration was 23 µg/m3. The pollution patterns measured indoors and outdoors are given in the figure below.

4

Figure 4. Indoor vs Outdoor PM2.5 concentrations profile comparison

On the other hand, indoor nitrogen dioxide concentration was significantly lower than outdoor pollution levels. The average outdoor concentration during the measurement period was 25 µg/m3 while the average concentration of 12 µg/m3. Both pollution patterns measured indoors and outdoors are given in the figure below.

5

Figure 5. Indoor vs Outdoor NO2 concentrations profile comparison

4. Conclusion

The comparison of the indoor and outdoor pollution levels showed a very low correlation between the 2 environments. Therefore, Airscan once again confirmed the hypothesis that high indoor dust particle concentration observed in the station is generated by the train movement, braking and acceleration. Moreover, doors opening and movement of passengers through the platform line have a certain contribution to the high pollution levels. On the other hand, the pollution levels measured within the stations are much lower compared to the outdoor NO2 levels.

In the coming months, Airscan will continue to work on the project and will share the results on our webpage.