No abstract

Quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), known as low-Z particle EPMA, and Raman microspectrometry (RMS) were applied in combination for an analysis of the iron species in airborne PM10 particles collected in underground subway tunnels. Iron species have been reported to be a major chemical species in underground subway particles generated mainly from mechanical wear and friction processes. In particular, iron-containing particles in subway tunnels are expected to be generated with minimal outdoor influence on the particle composition. Because iron-containing particles have different toxicity and magnetic properties depending on their oxidation states, it is important to determine the iron species of underground subway particles in the context of both indoor public health and control measures. A recently developed analytical methodology, i.e., the combined use of low-Z particle EPMA and RMS, was used to identify the chemical species of the same individual subway particles on a single particle basis, and the bulk iron compositions of airborne subway particles were also analyzed by X-ray diffraction. The majority of airborne subway particles collected in the underground tunnels were found to be magnetite, hematite, and iron metal. All the particles collected in the tunnels of underground subway stations were attracted to permanent magnets due mainly to the almost ubiquitous ferrimagnetic magnetite, indicating that airborne subway particles can be removed using magnets as a control measure.

We removed particulate matter (PM) emitted from a subway tunnel using magnetic filters. A magnetic filter system was installed on the top of a ventilation opening. Magnetic field density was increased by increasing the number of permanent magnet layers to determine PM removal characteristics. Moreover, the fan's frequency was adjusted from 30 to 60 Hz to investigate the effect of wind velocity on PM removal efficiency. As a result, PM removal efficiency increased as the number of magnetic filters or fan frequency increased. We obtained maximum removal efficiency of PM10 (52%), PM2.5 (46%), and PM1 (38%) at a 60 Hz fan frequency using double magnetic filters. We also found that the stability of the PM removal efficiency by the double filter (RSD, 3.2-5.8%) was higher than that by a single filter (10.9-24.5%) at all fan operating conditions.

Abstract-Noble (Pt, Pd) and transition metals (Mn, Cu) were employed as coupling catalysts to evaluate the toluene (1500 ppm C of initial concentration) removal efficiencies in the electron beam (EB)-catalyst coupling system. The toluene removal efficiency was 60.1% in the EB-only system at a dose of 8.7 kGy. In the presence of the metal catalysts (Pt, Pd, Cu and Mn), the removal efficiency was enhanced by 37, 33, 6 and 22%, respectively, compared to that of EB-only treatment. It was found that the selectivity to CO 2 with Pt and Pd coupling were relatively higher than those of Cu and Mn. Especially the CO 2 selectivity of EB-Pt coupling was significantly high at a relatively low absorbed dose. The removal efficiencies were compared for loading of catalyst and there was no significant difference among 0.1, 0.5 and 1.0 wt%.

Adsorbent combination studies have been carried out to remove nitrogen dioxide (NO 2 ) and volatile organic compounds (VOCs: BTEX) out of a subway environment characterized by high flow and low concentration. Optimal conditions for the high removal efficiency of the concerned target compounds were obtained through testing a series of control factors such as adsorbent sorts, thicknesses, and superficial velocity. It was found that the efficiencies increased as the specific surface area of activated carbon and its thickness increased, and external void fraction decreased. Furthermore, mixed activated carbon with granular and constructed contents was extensively tested to reduce pressure drop through the carbon bed. It was found that the performance of higher contents of granular activated carbon was better than that of higher contents of the constructed carbon. When the mixed carbon was applied to the subway ventilation system in order to eliminate NO 2 and VOC simultaneously, the removal efficiencies were found to be 75% and 85%, respectively.