Airborne particulate matter in the subway system of Vienna

Abstract

Since its opening more than 40 years ago, the subway system in Vienna affirmed itself as an elemental part of the capital`s infrastructure. While subway systems are offering a convenient and environmentally friendly option of getting around in major cities all around the world, recent studies of air quality in these microenvironments focused on the elevated particulate matter (PM) concentrations.In addition to a comprehensive literature survey a measurement campaign was performed at four different stations in six platform and tunnel locations to evaluate and characterize the PM10 levels using a Low Volume Sampler for gravimetric and chemical analysis, side by side with an Optical Particle Counter and an Electric Low-Pressure Impactor to identify the impact on air quality. The findings of the present study display elevated degrees of airborne ferruginous dust, depending predominantly on the rate of passing trains and number of commuters, producing daily repetitive trends of PM10 mass concentration variations. The mean PM10 concentrations ranged between 97 μg/m3 and 341 μg/m3 in the Viennese subway system, thereby placing it in an average position, with respect to subway PM concentrations in other European cities, described in the literature. A unique feature of the current work is that measurements were conducted within the tunnels and not only on the platforms. Within the dataset collected during this work, marked concentration differences between platform and tunnel locations couldn`t be confirmed. The proportionately coarse PM10-2.5 mode contributed a major share, with relative contributions between 45 % to 70 % to the PM10 mass concentrations. Meanwhile, the particle number concentrations were not elevated regarding common urban concentration values, reaching 1 - 2*104 #/cm3, influenced mainly by particles with a mean aerodynamic diameter less than 0.3 μm. Spatial and temporal concentration variations, monitored on the platform levels, were analyzed, and discussed with regard to factors like station designs and train frequencies, inter alia. Further on, source analysis could identify PM sources within the subway system and, to a smaller extent, ambient influences as well.