Thermogravimetry coupled with mass spectrometry measurements of individual coal (SF), individual walnut shell (WS), and their blends were performed. Interaction between the coal and the WS, activation energy, and reaction mechanism, were determined. Evolution profiles of volatile products before 1173 K were also elaborated. It was shown that incorporation of the coal into the WS, enhanced apparent activation energies of the blends in 533-613 K; synergistic reactions happened in approximately 573-773 K, for the blends excluding SF/WS (1:1), bringing about improved emissions of acetic acid; mass ratio of the coal to the WS at 1:2, was more favourable to the improvement, maximum relative intensity of emission being 3.11 x 10(-10) A/g; carbonyl and carboxyl containing species, from pyrolysis of the WS and the coal in 573-673 K, contributed to the improvements, through radicals stabilization, deacetylation and isomerizadon. A possible copyrolysis synergy mechanism, relevant to gases emission, was proposed based on experimental results.