Optical properties of fine particulate matter in Upper Silesia, Poland

Ambient particles whose aerodynamic diameters were not greater than 2.5 μm (fine fraction of Particulate Matter; PM_2.5) and 1 μm (PM₁; sub-fraction of PM_2.5) were sampled at three sites in Upper Silesia (Poland): urban background site, rural background site, and urban traffic site. In total, 240 samples were collected between 2 August 2009 and 27 December 2010. The reflectance of the collected PM₁ and PM_2.5 samples was determined with a digital smoke stain reflectometer. The 24-h courses and seasonal changes of three determined optical parameters for PM₁ and PM_2.5 (absorption coefficient (a), mass absorption (σ), and mean light reflection coefficient (R_av)) were illustrated and discussed. The mean values of the regional background absorption coefficient (a) were 1.27 × 10^-5 m^-1 and 0.87 × 10^-5 m^-1 for PM_2.5 and PM₁, respectively. In Katowice (urban background), the mean absorption levels were 2.37 × 10^-5 m^-1 and 2.09 × 10^-5 m^-1 for PM_2.5 and PM₁, respectively. The highest values of the absorption coefficient for both PM fractions were found close to the highway (urban traffic site). In the heating season (winter), the absorption coefficient (a) for PM_2.5 and PM₁ increased significantly when compared with the non-heating season. The obtained results confirmed the thesis about the significant increase in the elemental PM_2.5-bound carbon concentration caused by the intensified hard coal combustion in Upper Silesia in winter. Moreover, it turned out that the increase in the concentration of the PM_2.5-bound sulphates was even higher, which resulted in the relative decrease of the elemental carbon content in this PM fraction in some areas. Consequently, the mass absorption value dropped there as well.