Abstract
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.
Highlights
The visibility is a significant index for air quality and weather observation (Waston, 2002; Chang et al, 2009; Che et al, 2009; Carbone et al, 2013)
The results showed that the surface area concentration had a great relationship with extinction coefficient, especially for PM2.5
It was quite obvious that the particle surface area concentration increased as the relative humidity was above 70%, compared with the drier condition
Summary
The visibility is a significant index for air quality and weather observation (Waston, 2002; Chang et al, 2009; Che et al, 2009; Carbone et al, 2013). Previous studies showed that the urbanization and industrialization conduced the air pollution emission increased and the visibility decreased (Qiu and Yang, 2000; Fan et al, 2005). Tsai (2005) found that the average length of visibility was 12.4 ± 4.2 km from 1961 to 2003 in Tainan, Taiwan. The visibility loss was influenced by air pollutions which were from vehicular emission and fossil-fuel burning (Goyal and Sidhartha, 2003; Tsai, 2005). The visibility decreased about 2.1 km every ten years from 1990 to 2005 which was affected by the urbanization and industrialization (Zhang et al, 2004; Che et al, 2007; Chen et al, 2012). Kim et al (2006) had pointed out that the visibility was affected by fine particle (PM2.5) emission directly or indirectly. The atmospheric particles affect human health, and visibility
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