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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, SO 2 , NO x , and PM 10 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, SO 2 , NO x, and PM 10 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.

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Although several studies have explored green adsorbent synthesized from many types of agriculture waste, this study represents the first attempt to prepare an environmentally friendly rice bran/SnO2/Fe3O4-based absorbent with economic viability and material reusability, for the promotion of sustainable development. Here, rice bran/SnO2/Fe3O4 composites were successfully synthesized and applied for adsorption of reactive blue 4 (RB4) and crystal violet (CV) dyes in aqueous solutions. The adsorption data were well-fitted by the Langmuir isotherm model and the pseudo-second-order kinetic model. The maximum adsorption capacities of the RB4 and CV dyes as indicated by the Langmuir isotherm model were 218.82 and 159.24 mg/g, respectively. As results of response surface methodology (RSM) showed, the quadratic model was appropriate to predict the performance of RB4 dye removal. The findings exhibited that an optimum removal rate of 98% was achieved at 60 °C for pH 2.93 and adsorption time of 360 min. Comparative evaluation of different agricultural wastes indicated that the rice bran/SnO2/Fe3O4 composite appeared to be a highly promising material in terms of regeneration and reusability, and showed that the composite is a potential adsorbent for dye removal from aqueous solutions. Overall, the study results clearly suggest that an adsorbent synthesized from rice bran/SnO2/Fe3O4 magnetic particle composites provides encouraging adsorption capacity for practical applications for environmental prevention.