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Thermal-optical evolved gas analysis (TOEGA) is a conventional method forclassifying carbonaceous aerosols as organic carbon (OC) and elementalcarbon (EC). Its main source of uncertainty arises from accounting forpyrolized OC (char), which has similar behavior to the EC originally presenton the filter. Sample composition can also cause error, at least partly bycomplicating the charred carbon correction. In this study, lab generatedmetal salt particles, including alkali (NaCl, KCl, Na2SO4),alkaline-earth (MgCl2, CaCl2) and transition metal salts(CuCl2, FeCl2, FeCl3, CuCl, ZnCl2, MnCl2,CuSO4, Fe2(SO4)3), were deposited on a layer of dieselparticles to investigate their effect on EC and OC quantification withTOEGA. Measurements show that metals reduce the oxidation temperature of ECand enhance the charring of OC. The split point used to determineclassification of EC vs. OC is more dependent on changes in EC oxidationtemperature than it is on charring. The resulting EC/OC ratio is reduced by0–80% in the presence of most of the salts, although some metal saltsincrease reported EC/OC at low metal to carbon ratios. The results implythat EC/OC ratios of ambient aerosols quantified with TOEGA have variablelow biases due to the presence of metals. In general, transition metals aremore active than alkali and alkaline-earth metals; copper is the mostactive. Copper and iron chlorides are more active than sulfates. The meltingpoint of metal salts is strongly correlated with the increase of OCcharring, but not with the reduction of EC oxidation temperature. Otherchemistry, such as redox reactions, may affect the EC oxidation. A briefdiscussion of possible catalytic mechanisms for the metals is provided

The effect of metal salts on quantification of elemental and organic carbon in diesel exhaust particles using thermal-optical evolved gas analysis