Carbon reacts with Na2SO4 in glass batches, influencing SOx emissions. To study the role of carbon active surface area (ASA) in the decomposition phenomena, Na2SO4 is reacted with three carbons with a wide ASA range. The decomposition behavior was evaluated by thermogravimetric analysis (TGA) and evolved gas analysis via mass spectrometry and Fourier transform infrared spectrometry. Higher carbon ASA yields lower decomposition temperatures. SOx emissions are realized at temperatures as low as 773 K. Isothermal Na2SO4-C decomposition initiates via the nucleation of Na2S. The rate constants for the nucleation regime are normalized against ASA, yielding an activation energy of 275 kJ/mol for nucleation.