Absorption coefficients and mass concentrations of the urban aerosol of Vienna, Austria, during the years 1985 and 1986

Abstract

Nearly every day aerosol absorption coefficients and mass concentrations were measured at the physics building of the University of Vienna, located approximately 1.5 km from the city center. The aerosol was deposited on Nuclepore filters with 0.2 μm pore size, which were analyzed both gravimetrically for mass concentration c _m and by the integrating plate method for absorption coefficients (σ _a ). The overestimation of the method was corrected for using calibration factors derived from Hitzenberger (1993) and Hitzenberger and Puxbaum (1993).

A statistical analysis showed marked seasonal changes of both σ _a and c _m with lowest values in summer (σ _a below detection limit, c _m =21.1 μg/m³) and highest in winter (σ _a =0.574 km⁻¹, c _m = 543.1 μg/m³).The monthly averages ranged from σ _a =0.014 km⁻¹ (July 85) to σ _a =0.127 km⁻¹ (Dec. 85). The monthly mean mass concentration had a low in June 85 (44.5 μg/m³) and a maximum of 159 μg/m³ in February 85. A marked dependence on the wind direction was found for both σ _a and c _m , although the wind directions of the maximum values do not match. An estimate of the black carbon (BC) content using a value of the specific absorption coefficient B _a for BC of 8 m 2/g showed that mean winter BC-concentrations were higher by a factor of 5.2 than in summer, although mass concentrations were increased by only a factor of 2. From seasonal and weekly variation patterns it can be estimated that heavy duty diesel traffic contributes 63 % of the absorbing aerosol in summer. In winter the main BC source is space heating (54 % during the week, 85 % on Sundays); followed by heavy duty traffic (27 % during the week, absent on Sundays).

Mean single scattering albedos ω ₀ in winter were as low as 0.70 and in summer as high as 0.94, although individual days had ω ₀ below the critical value of 0.85.