| 英文摘要 |
The vehicle exhaust is one of the major air pollution sources in the modern cities. To monitor and control the particulate matter emission of in-use vehicles is a critical and important means to improve the air quality. The main purposes of the present study was to develop a real-time, low cost and simple method to measure vehicle exhausted PM. The work might be helpful for environmental policy making and eventually environment improvement.
The sampling and measurement system was design to include a chamber adapter connecting to tailpipe, a dehumidifying unit, and aerosol size-selective device, and an appropriate measurement. Aerosol instruments, such as SMPS, CPC, black carbon aerosol monitor (AE51), and filter were used to measure the particle size distribution, number concentration, black carbon concentration and PM mass, respectively. The effects of temperature, humidity, condition time on the filter weighting were evaluated. A high resolution nano-DMA was used to measure aerosol penetration through the volatile particle remover (VPR), as function of aerosol size with the lower limit down to 2.5 nm. The penetration test was conducted using sodium chloride as non-volatile agent to validate the effect of VPR temperature on the aerosol deposition. The change in size distribution and number concentration of motorcycle exhaust particles was then used to determine whether the homogeneous nucleation exited during the cooling down process. The relationship between SPN, mass and AE51 measurements were also evaluated.
The results indicated that the PTFE filter was the most appropriate media for sampling particulate matter. The mass decrease due to semi-volatile matter decreased with increasing temperature of the sampling filter holder. The black carbon concentration was not affected by the semi-volatile matter and could be used as an index to infer the mass concentration. The AE51 had a good relationship with the SPN method. The VPR reduced the particle size and resulted in the underestimation of particle number concentration, probably due to some of the particles smaller than 2.5 nm, the lower detection limit of ultrafine condensation particle counter. The homogeneous nucleation was not observed in the motorcycle exhaust.
The regression analysis showed a good relationship between PFDS and CVS results of particle number and black carbon measurement. The mass concentration had a poor relationship between these two dilution systems due to the low particle emission. The method developed by this study had advantages of easy, convenient, and real-time measurement and suitable for the vehicle particulate emission.
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