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Understanding characteristics of diurnal particle concentration variation in an underground subway tunnel is important to reduce subway passengers' exposure to high levels of toxic particle pollution. In this study, real-time particle monitoring for eight consecutive days was done at a shelter located in the middle of a one-way underground subway tunnel in Seoul, Republic of Korea, during the summer of 2015. Particle mass concentration was measured using a dust monitor and particle number concentration using an optical particle counter. From the diurnal variations in PM 10 , PM 2.5 , and PM 1 , concentrations of particles larger than 0.54 μm optical particle diameter were affected by train frequency whereas those of particles smaller than 0.54 μm optical particle diameter were not changed by train frequency. Number concentration of particles smaller than 1.15 μm optical particle diameter was dependent on outdoor ambient air particle concentration level, whereas that of particles larger than 1.15 μm optical particle diameter was independent of outdoor ambient air due to low ventilation system transmission efficiency of micrometer-sized particles. In addition, an equation was suggested to predict the diurnal particle concentration in an underground tunnel by considering emission, ventilation, and deposition effects.

Exposure to airborne particulate matter (PM) causes several diseases in the human body. The smaller particles, which have relatively large surface areas, are actually more harmful to the human body since they can penetrate deeper parts of the lungs or become secondary pollutants by bonding with other atmospheric pollutants, such as nitrogen oxides. The purpose of this study is to present the number of PM inhaled by subway users as a possible reference material for any analysis of the hazards to the human body arising from the inhalation of such PM. Two transfer stations in Seoul, Korea, which have the greatest number of users, were selected for this study. For 0.3-0.422 μm PM, particle number concentration (PNC) was highest outdoors but decreased as the tester moved deeper underground. On the other hand, the PNC between 1 and 10 μm increased as the tester moved deeper underground and showed a high number concentration inside the subway train as well. An analysis of the particles to which subway users are actually exposed to (inhaled particle number), using particle concentration at each measurement location, the average inhalation rate of an adult, and the average stay time at each location, all showed that particles sized 0.01-0.422 μm are mostly inhaled from the outdoor air whereas particles sized 1-10 μm are inhaled as the passengers move deeper underground. Based on these findings, we expect that the inhaled particle number of subway users can be used as reference data for an evaluation of the hazards to health caused by PM inhalation., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In this study, we measured the size distribution of particles ranging in size from 5.6 to 560 nm that were emitted between brake disks and pads under various braking conditions to observe and analyze changes to the resulting particle size distribution over braking time. A peak of 178-275 nm (200 nm peak) was observed in all braking conditions. However, the generation of spherical particles of a 10 nm range was observed only when the disk speed and brake force were above certain levels and intensified only when speed and brake force further increased. The total number concentration of ultrafine particles (no larger than 0.1 μm; PM0.1) generated was found to correlate with disk speed and brake force. Thus, the generation of nanoparticles resulting from disk speed and brake force was attributable primarily to increases in the contact surface temperature. The critical temperature for the generation of nanoparticles of a 10 nm range was found to be about 70 °C, which is the average temperature between the surface and the inside of the disk. If the speed or brake force was higher, that is, the temperature of the contact surface reached a certain level, evaporation and condensation took place. Vapor then left the friction surface, met with the air, and quickly cooled to form nanoparticles through nucleation. When the newly generated particles became highly concentrated, they grew through coagulation to form agglomerates or the vapor condensed directly onto the surface of existing particles of about 200 nm (formed by mechanical friction).

Given that around eight million commuters use the Seoul Metropolitan Subway (SMS) each day, the indoor air quality (IAQ) of its stations has attracted much public attention. We have monitored the concentration of particulate matters (PMx) (i.e., PM10, PM2.5, and PM1) in six major transfer stations per minute for three weeks during the summer, autumn, and winter in 2014 and 2015. The data were analyzed to investigate the relationship between PMx concentration and multivariate environmental factors using statistical methods. The average PM concentration observed was approximately two or three times higher than outdoor PM10 concentration, showing similar temporal patterns at concourses and platforms. This implies that outdoor PM10 is the most significant factor in controlling indoor PM concentration. In addition, the station depth and number of trains passing through stations were found to be additional influences on PMx. Principal component analysis (PCA) and self-organizing map (SOM) were employed, through which we found that the number of trains influences PM concentration in the vicinity of platforms only, and PMx hotspots were determined. This study identifies the external and internal factors affecting PMx characteristics in six SMS stations, which can assist in the development of effective IAQ management plans to improve public health., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Biomass fuel is used for cooking and heating, especially in developing countries. Combustion of biomass fuel can generate high levels of indoor air pollutants, including particulate matter (PM) and volatile organic compounds (VOCs). This study characterized PM and VOC emissions from cow dung combustion in a controlled experiment. Dung from grass-fed cows was dried and combusted using a dual-cone calorimeter. Heat fluxes of 10, 25, and 50 kW/m(2) were applied. The concentrations of PM and VOCs were determined using a dust spectrometer and gas chromatography/mass spectrometry, respectively. PM and VOC emission factors were much higher for the lower heat flux, implying a fire ignition stage. When the heat flux was 50 kW/m(2), the CO2 emission factor was highest and the PM and VOC emission factors were lowest. Particle concentrations were highest in the 0.23-0.3 μm size range at heat fluxes of 25 and 50 kW/m(2). Various toxic VOCs, including acetone, methyl ethyl ketone, benzene, and toluene, were detected at high concentrations. Although PM and VOC emission factors at 50 kW/m(2) were lower, they were high enough to cause extremely high indoor air pollution. The characteristics of PM and VOC emissions from cow dung combustion indicated potential health effects of indoor air pollution in developing countries.

Numerous reports have shown that fine particulates threaten human health. Since their health impact is associated with both mass and number concentrations, it is necessary to evaluate the emission standards for particulate mass accordingly. This study examined the particulate matter characteristics of diesel locomotive engine exhaust at various engine ratings. Diesel engine exhaust was collected via a dilution tunnel and the concentration and size distribution of fine particles were measured by a scanning mobility particle sizer. Exhaust gasses were measured simultaneously by a stack sampler. The maximum carbon monoxide emission was reached at 59% of the maximum rating, after which emissions decreased. The particle count median diameter increased with the engine rating, until a maximum was reached at 40% of the maximum rating. Most exhaust particles were nanoparticles with the nuclei mode range, a particle diameter (D(P))<50 nm. The increase in particles with the accumulation mode range, 50

We analyzed the size-dependent volatility of nanoparticles in a diameter range of 30-70 nm in diesel exhaust emissions. The test system included a medium-duty diesel truck on a chassis dynamometer, a single-stage dilution tunnel, a tandem differential mobility analyzer (TDMA) equipped with an electric furnace, and a condensation particle counter. The size shifts of monodispersed diesel nanoparticles under changing furnace temperatures were measured by TDMA in the gas phase. Together with the reduction of average particle size and volume, we observed the development of bimodal size distributions resulting from the separation between semivolatile and nonvolatile species as the furnace temperature was increased. While 91-98% of the particles were found to be semivolatile species by total volume during the idling engine condition, only 6-9% were semivolatile during the one-half engine load condition. We also found that smaller particles contained a larger fraction of semivolatile species.