A novel microsphere microreactor approach was used to capture the real-time dynamics of fast pyrolysis of single biomass microspheres using fast flame ionization detection at a data capture rate of 10,000 Hz. Time-domain pyrolysis data were transformed temperature domain using a model-based approach. The apparent kinetics of pyrolysis was systematically investigated as a function of size and type of biomass particle and reactor temperature. A mechanism for fast pyrolysis of crystalline cellulose that suggests a parallel series dependent pathway is proposed and supported.