Results of the "carbon conference" international aerosol carbon round robin test stage I

An international round robin test on the analysis of carbonaceous aerosols on quartz fiber filters sampled at an urban site was organized by the Vienn a University of Technology. Seventeen laboratories participated using: nine different thermal and optical methods. For the analysis of total carbon (T C), a good agreement of the values obtained by all laboratories was found ( 7 and 9% r.s.d.) with only two outliers in the complete data set. In contra st the results of the determination of elemental carbon (EC) in two not pre -extracted samples were highly variable ranging over more than one order of magnitude and the relative standard deviations (r.s.d.) of the means were 36.6 and 4.5%. The laboratories that obtained similar results by using meth ods which reduce the charring artifact were put together to a new data set in order to approach a "real EC" value. The new data set consisting of the results of 10 laboratories using seven different methods showed 16 and 24% lower averages and r.s.d. of 14 and 24% for the two not pre-extracted sampl es. Taking the current filters as "equivalents" for urban aerosol samples w e conclude that the following methods can be used for the analysis of EC in carbonaceous aerosols: thermal methods with an optical feature to correct for. charring during pyrolysis, two-step thermal procedures reducing charri ng during pyrolysis, VDI 2465/1 method (removal of OC by solvent extraction and thermodesorption in nitrogen) and the VDI 24652 method (combustion of OC and EC at different temperatures) with an additional pre-extraction with a dimethyl foramide (DMF)/toluene mixture. Only thermal methods without an y correction for charring during pyrolysis and the VDI 2465/2 method were o utside the range of twice the standard deviation of the new data set. For a filter sample pre-extracted with the DMF/toluene mixture the average and r .s.d. from all laboratories (20.7 mu gC; 24.4% r.s.d.) was very similar as for the laboratory set reduced to 10 laboratories (20.6 mu gC; 19% r.s.d.). Thus DMF pre-extraction appears to improve the performance of the thermal methods without charring during pyrolysis control, e.g. the VDI 2465/2 meth ods. (C) 2001 Elsevier Science Ltd. All rights reserved.