INTERNATIONAL ROUND-ROBIN TESTS ON THE MEASUREMENT OF CARBON IN DIESEL EXHAUST PARTICULATES

Object: Diesel soot has been recognized as probably carcinogenic to hu mans. Elemental carbon (also called black carbon) in soot is considere d at the moment as the most significant surrogate to be measured for a ssessing the exposure to this pollutant. Its analysis is done by combu stion in an oven and determination of the CO2 formed, after eliminatio n of the organic fraction of the soot by heating and/or by solvent ext raction. The analysis allows determination of both fractions of the so ot: ''elemental carbon'' (EC) and organic carbon (OC). The sum of EC a nd OC is called TC (total carbon). Method: An informal European coordi nation group organized two round robin tests on filter Samples collect ed from diluted diesel emissions. The first round (RRT1) was performed on 13 different samples analyzed by ten laboratories. The range of lo ading was 2.5 to 150 mu g/cm(2) of EC. No evaluation of the precision within laboratories could be made since each laboratory gave only one result per sample. Therefore a second round (RRT2) was organized with two samples and a blank filter sent in several portions to 11 laborato ries. It should be stressed that each laboratory used its own method a nd that no standardization was planned at this stage. Results: Results of RRT1 showed that the coefficient of variation between laboratories decreased with higher loading and was around 10% to 15% for EC above about 20 mu g/cm(2). Dispersion of the results varied and it appeared that the way OC is removed from the soot is probably the most importan t factor of influence. The correlation between the laboratories was go od as a whole but some systematic differences could be detected. Besid es the different techniques to remove the organic carbon, the pretreat ment of the filter by HCl (either as a vapor or as a solution) to remo ve the inorganic carbonates (potential interference sources), is proba bly also a significant factor of influence in the dispersion of the re sults between laboratories. It is not yet clear from these results whe ther the ''environmental'' laboratories give different results from th e ''occupational'' laboratories, but it is clear that their objectives differ since for the ''environmentalists'', EC is not a specific mark er of diesel immissions, in contrast to the ''occupationalists'' Concl usion: It can be concluded that, although significant differences exis t between laboratories they can be attributed mainly to the narrow dis tribution of the results within a single laboratory, and that the over all agreement of the results for EC and TC is fairly good. These resul ts obtained with pure diesel engine emissions, should be complemented by field samples, but they have already achieved relevant findings in the performance of the procedures used to assess exposure to diesel so ot.