Known constituents of tobacco (cellulose, pectin, lignin, protein, chlorogenic acid, and rutin) were subjected to fractional pyrolysis over the temperature range of 240-510 degrees C in a specially constructed, high-temperature flow reactor system. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze for free radicals in the initially produced total particulate matter (TPM) and in TPM that was allowed to age with exposure to air and light. The TPM formed during pyrolysis of cellulose, pectin, and rutin did not contain any radicals, whereas radicals in the TPM of protein, lignin, and chlorogenic acid increased with increasing pyrolysis temperature. The nature of the EPR spectra of the initially formed radicals (primary radicals) depended on the chemical structure of the constituent and temperature of pyrolysis. New types of free radicals were observed after exposure of the TPM to light and air (secondary radicals), but the nature of the EPR spectra was remarkably similar for all constituents. Only chlorogenic acid produced TPM in which the concentration of radicals decreased with exposure to air. Mixtures of the constituents, proportional to their abundance in tobacco leaves, represented the yield of radicals in TPM at temperatures above 375 degrees C reasonably well, but not below this temperature, suggesting that (1) another, untested constituent in tobacco is responsible for radical formation or that (2) TPM from tobacco contains additional constituents that promote radical stabilization and/or formation.