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Over the recent years, the continued increase in the number of particles in air has become a public concern. This problem can be addressed by using nanofibers to filter fine particles. However, nanofibers possess complex characteristics. As such, the effects of surface charge require further studies. In this study, the surface voltages of nanofibers were analyzed with an electrometer after these fibers were charged through corona discharge to investigate the mechanism of filtration. Results indicated that the surface voltage of 2.0% TiO2 polyacrylonitrile fibers (TPFs) can reach up to 0.97 kV and then decrease to 0.60 kV after 96 h. Particles were optimally removed by charged polyacrylonitrile fibers (PFs) and TPFs. Particle penetration decreased by 71% of TPF and 36% of PF. Scanning Electron Microscopy and Nitrogen adsorption/desorption isotherms revealed that increasing the surface area and roughness of these materials are more favorable for charge maintenance to promote particle removal. Our research could provide an in-depth understanding of the effects of surface charge on particle removal and show how systems can be optimized for further applications.

Arid riverbed is an important source of Aeolian dust to influence the atmosphere of nearby village or downtown. In general, Aeolian dust pertains to wind activity in the study of geology, environment and meteorology on particle suspension. This field study set the horizontal/vertical sampling system up in order to investigate the Aeolian dust dimensional distribution properties from the riverbed of the Jhuoshuei River. In addition, the study utilized the unmanned aerial vehicle (UAV) imagery to discriminate the covering condition of riverbed. The results revealed that the percentage of riverbed covering conditions, including bare zone, wetlands, green covering and water covering was about 50.1, 15.7, 16.8 and 17.4%, respectively, on January 5th, 2011. Two Aeolian dust cases from riverbed were measured on November 26th, 2010 and January 15th, 2011. First sampling case was under slower wind speed, and the total particulate matter (PM) concentration in vertical sampling was almost decreased with increasing sampling height, however, the phenomena of second case (faster wind speed) was just on the contrary. Besides, Aeolian dust was distributed in a bimodal or a multimodal curve, and the main peak size was above 10 μm. Mode size of suspension particle diameter was increased as the wind speed increased (14.8 μm/ first case; 21.3 μm/ second case). The total mass concentration ratio of south site to source site (one meter height) was about 1:9 in first case and about 1:3 in second case. Comparing with those two cases, the faster the wind is, the shorter the surface roughness height is (3.08 mm/ first case; 1.07 mm/ second case). Besides, as the wind speed increasing, the friction velocity was also increased (0.33 m s–1/ first case; 0.68 m s–1/ second case). Consequently, this study clued the spatial variability of river dust events, which can further aid the site investigating, forecasting and preventing of dust influences.

The long tunnel is a fixed, semi-closed environment where excessive concentrations of air pollutants are easily accumulated. This can potentially have a serious affect on drivers' health, especially when operating vehicles in the long tunnel for a lengthy period of time. Therefore, studies on pollutant emission characteristics and influential factors of emission in the tunnel are important. In this study, several sampling sites were arranged in the 12.9 km long Hsueh-shan Tunnel, to help understand the piston effect of pollutant emission characteristics and spatial concentration distribution. In order to understand the influential factor of air quality in the long tunnel, several tests were run during a closed period, an open period, a non-rush hour period, and a rush hour period. The results showed that during the closed period, the CO, SO2, NOx, and PM10 concentrations in the Hsueh-shan Tunnel were in the range of: 0.58–0.64 ppm, 0.94–1.08 ppb, 6.33–7.11 ppb, and 45.4–54.3 μg/m 3 , respectively. In contrast, during the open period, the CO, SO2, NOx, and PM10 concentrations reached 12–39 ppm, 20–48 ppb, 1.2–3.1 ppm, and 75–177 μg/m 3 , respectively. In the Hsueh-shan Tunnel, the number of vehicles at rush hour was about 1400 per hour, three times higher than during non-rush hour. The piston effect is very obvious since pollutant concentrations are elevated with increasing distance from the inlet. This study found that the pollutant concentration near the outlet can be three times higher than that near the inlet.