The object of this study investigated the correlation of visibility with aerosol physical properties in the urban atmosphere. The field experiments were conducted in four seasons from August 2010 to March 2011 in National Taipei University of Technology (NTUT), located in the downtown of Taipei city. Integrating nephelometer was used to measure the aerosol optical properties and compared with the calculated values based upon the measurements of aerosol concentration and size distribution. The characterization of visibility was influenced by aerosol concentrations and relative humidity. When the relative humidity was above 70%, the particles usually grew into larger size range and changed their optical characteristics. The results showed that the surface area concentration had a great relationship with extinction coefficient, especially for PM 2.5 . The correlation between particle number or volume concentration and extinction coefficient was complicated. Hence, visibility could be estimated by particle surface area concentration. The conclusions suggested that particle surface area concentration obtained from number concentration combined with size distribution could be used to estimate visibility.
Particle back-corona slows the efficiency of the dry-electrostatic precipitator (dry-ESP), especially during the removal of high resistivity particles. In this study, a new type of wetelectrostatic precipitator (wet-ESP) was designed and built using stainless steel (SS), conductive glass (CG), and original glass (OG) for its collection plates. The objectives of this research included the efficiency characteristics of both the dry-ESP and the wet-ESP, how the materials used in the dust collectors affect the ESP performance including SS, CG, and OG, and the effects on the electric resistivity of the particle of its performance, and the ozone generation rates of the wet-ESP. The experiment results indicated that the wet-ESP could improve the dust-cake phenomenon caused by high electrical resistivity particles that often occurred on dry-ESP in order to prolong its efficiency. Furthermore, the results indicated that during the most penetrating particle size (MPPS) penetration of SSESP and CGESP were both below 6% while OGESP was over 40% under the dry condition. When OGESP was placed and operated under the wet condition, its particle penetration dropped to below 20% under the MPPS. The results confirmed that compared to the dry-ESP, wet-ESP performed at a higher and better efficiency. In addition, as ozone concentration acts on the corona current under the same voltage, the result found that the ozone concentration of OGESP was lower than both CGESP and SSESP under the wet setting.
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