Thermal/optical carbon analysis is based on the preferential oxidation of OC and EC materials under different temperatures and atmospheres. A ~0.5 cm² punch from a particle laden quartz fiber filter is heated in programmed temperature steps. Organic compounds are liberated under a non-oxidizing helium atmosphere at lower temperatures up to 580 °C, while EC is combusted in an oxidizing atmosphere with 2% O₂ at temperatures up to 840 °C. The liberated carbon is oxidized to carbon dioxide (CO₂) by heated manganese dioxide (MnO₂), and the CO₂ is quantified by an NDIR detector. Seven modulated diode lasers measure the reflectance from, and transmittance through, each filter at wavelengths from 405 to 980 nm.