Measuring Elemental Carbon in Occupational Environments

Abstract: Carbonaceous aerosol particles from combustion, such as diesel exhaust particles (DEP), harm human health and affect the Earth’s radiative system.Elemental carbon (EC) has been proposed to be used as a marker of DEP. The objective of this thesis was to investigate the EC levels in different environments, to compare methods for measuring EC and investigate confounding factors that influence EC. The five papers concluded the following: A study of asphalt paving work showed levels of respirable EC at 3 µg m-3 and organic carbon (OC) level at 42 µg m-3. The concentration of OC was not high enough to disturb the light absorption of EC in the analysis. The EC/TC ratio 0.067 indicated a large contribution of OC from the asphalt fumes.Water-soluble organic compounds (WSOC) were used to show that samples with wood smoke particles, both single source and ambient, resulted in a positive bias of 10-20 % in EC due to WSOC, but not for samples with DEP.Well-defined single source samples of DEP gave differing EC and even total carbon levels in an intercomparison between three different analysing methods. Bio fuels such as vegetable oils, animal fat and natural gas showed very large difference in the amount of EC.A study of aerosol in the subway shows that iron oxides interfere with the analysis of EC. Analytical result and the oxidation state of iron in samples after analysis differed between NIOSH and IMPROVE. Optical measurements of Black Carbon (BC) in the subway were higher than at street level, which was suspected to be an overestimation of BC due to iron oxides.The apparent attenuation cross section, σATN (m2/g) was compared for different samples, different protocols and varying load during thermo-optical analysis to validate the setting of the OC/EC split point. The results indicating a mixed combustion of pyrolytic carbon with EC and the assumptions forming the basis for setting a proper split time between EC and OC do not seem to be valid.