Mobile Measurements and Personal Sampling during the Subway Commuting to Analyze Metals, identify Hot-spots and determine the Spatiotemporal Variability of PM
Abstrakt
People in big cities and urban areas all over the world spend a considerable amount of time by commuting every day. Public transport is one of the most sustainable, environmentally friendly and effective ways. Hence, minimizing the exposure to harmful compounds contained in ambient particulate matter (PM) in transport should be a priority. Fine PM can penetrate to lungs and ultrafine even directly into the blood stream through the lung alveoli. Health effects ranging from respiratory diseases to cancer significantly reduce quality of life and can lead to premature deaths and have non-negligible economic effects.
Combustion processes (e.g. car emissions) are mostly subject of measures due to harmful compounds such as polycyclic aromatic hydrocarbons (PAHs), while non-exhaust emissions containing large quantities of heavy metals are not yet regulated. Particularly due to increasing electromobility, non-exhaust emissions are currently getting more attention.
Underground subway stations and tunnels are a specific micro-environment. Trains not only produce non-exhaust emissions (abrasion of brakes, rails, train wheels, rail catenary and pantographs) but their movement resuspend the dust and mix it within a limited volume of air. Dispersion of PM is dependent also on the quality of ventilation systems, which in unfavorable cases can introduce exhaust emissions from streets above (Martins et al, 2016, Minguillón et al, 2018).
Stationary measurement at platforms presented at many studies provide comprehensive characterization and daily PM variations but not spatiotemporal variability during the typical commuting ride.
Therefore, the approach of this study was to characterize subway PM emissions in Munich (Germany) by both mobile and stationary measurement techniques: 1) repeating the same route 3 times a day at morning, noon and evening 2) stationary measurements at selected platforms 3) various experimental rides for hot-spot identification.
For all the measurements and sampling, a ventilated aluminum box was used, which was equipped with instruments connected to omni-directional inlets (TSI) in the breathing zone height. The box attached to the frame rucksack was carried by an operator who was taking notes during the ride (place and time, amount of people, relevant events). PM size-distribution (OPS 3330, TSI) and particle number concentration (PNC; DISCmini, Testo) were measured with 1s time resolution, black carbon as a marker of combustion processes in 10s resolution (MA200, Aethlabs). Sampling was performed cumulatively (1-3 hours long) for metal analysis by ICPMS (Agilent) and scanning electron microscope analysis SEM (Zeiss) with an EDX detector (Oxford).
A high spatiotemporal variability of both PM and PNC was observed. The hot-spots of the underground (U-Bahn) were the largest transfer stations, where many people congregate (Ostbahnhof, Hauptbahnhof, Odeonsplatz). The highest observed PM10 concentrations exceeded 100 µg/m3. In comparison, the over-ground station (S-Bahn) had concentration mostly similar to ambient values due to good ventilation (Fig 1). In accordance with the literature, iron was the most abundant metal with concentrations up to 120 µg/m3.
Subway PM measurements using mobile techniques are less expensive and demanding than stationary measurements and a large area can be monitored in a reasonable time. Therefore, this approach could be used in many cities world-wide for a realistic estimation of personal exposure and identification of hot-spots, which could then lead to effective actions by decision makers. This research is funded by dtec.bw - Digitalization and Technology Research Center of the Bundeswehr (project MORE).
Martins, V. et al. (2016) Environmental Research. 146, 35-46.
Minguillón et al. (2018) Environmental Research. 167, 314-328