Cite this article: Cheng, Y.C., Liang, C.S., Syu, J.Y., Chang, Y.Y., Yan, Y.L., Chen, S.J., Chen, C.C. and Lin, W.Y. (2015). Characteristics of Aerosol Extinction Coefficient in Taipei Metropolitan Atmosphere.
Aerosol Air Qual. Res.
15: 1823-1835. https://doi.org/10.4209/aaqr.2015.03.0132
Visibility impairment is a major problem in urban area.
One of the important indices of visibility is the extinction coefficient.
The characterization of visibility was influenced by aerosol concentrations and relative humidity.
Visibility could be estimated by particle surface area concentration.
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 PM2.5. 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.
Keywords: Visibility; Number concentration; Extinction coefficient; Surface area concentration