METHOD COMPARISON STUDY ON SOOT-SELECTIVE TECHNIQUES

In a long-term field study at two locations with different air polluti on levels several soot-selective measurement techniques were compared with a thermochemical method which measures non-extractable carbon (NE C) detecting the evolved CO2 by means of coulometric titration. The at tenuation measurement technique (aethalometer) and the aerosol photoem ission method showed good correlations to NEC for concentrations rangi ng from 1.6 mug/m3 to 40.8 mug/m3. The specific mass absorption coeffi cient of black carbon with respect to NEC varied between 8.4 m2/g and 13.7 m2/g with respect to the measurement sites, but the sigma value w as found to remain constant at each site independent of seasonal or me teorological variations. The ratio of photoelectric signal to NEC vari ed between 16 fA.(mug/m3)-1 and 33 fA.(mug/m3)-1 depending on the age of the aerosol. The diurnal variations of that ratio showed strong sim ilarities to the traffic patterns. Additionally a slight temperature d ependence of this ratio was found for the aged aerosol with a proporti onality factor of -0.35fA.(K.mug/m3)-1. With the reflectance measureme nt technique (smoke shade method) reliable NEC determination was not p ossible for NEC concentrations less-than-or-equal-to 5 mug/m3.