TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The vapor component residence time in the lower reaction zone is 0.1-5 (preferably 0.5-3) seconds. The vapor component residence time in the upper reaction zone is at least 400% greater than the vapor component residence time in the lower reaction zone. The average horizontal cross-sectional area of the upper reaction zone is greater than the average horizontal cross-sectional area of the lower reaction zone. The average horizontal cross-sectional area of the upper reaction zone is at least 50% (preferably at least 150%) greater than the average horizontal cross-sectional area of the lower reaction zone. The lower reaction zone is maintained at an average pyrolysis temperature and the upper reaction zone is maintained at an average cracking temperature, where the average pyrolysis temperature is 200-1000 degrees C (preferably 300-600 degrees C) and the average cracking temperature is at least 10 degrees C (preferably at least 50 degrees C) less than the average pyrolysis temperature. The length-to-diameter ratio of the lower reaction zone and the length-to-diameter ratio of the upper reaction zone are 2-20 (preferably 4-10). The riser reactor comprises a transition zone disposed between the upper and lower reaction zones, where the horizontal cross-sectional area of the transition zone increases upwardly, and the temperature control system is configured to introduce the thermal modification medium into the transition zone.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The process further comprises introducing a cracking catalyst into the lower reaction zone, where the cracking of step (c) comprises catalytic cracking. The pyrolyzing of step (a) converts at least 25 (preferably 50) wt.% of the solid particulate biomass into vapor components of the initial pyrolysis product. The cracking of step (c) converts at least 25 wt.% of the non-volatile components of the initial pyrolysis product into volatile components. Preferred Components: The thermal modification medium and quenching medium comprise liquid pyrolysis products, gaseous pyrolysis products, particles of a cracking catalyst, steam, lift gas and/or particles of an inorganic solid. The vapor components of the initial pyrolysis product comprises volatile components and non-volatile components, where the volatile components vaporize at less than 200 degrees C at 172 pa and the non-volatile components vaporize at greater than or equal to 200 degrees C at 172 pa, and the cracking of step (c) converts at least 10 wt.% of the non-volatile components of the initial pyrolysis product into volatile components. The cracked pyrolysis product exhibits (i) a concentration, by weight, of oxygen-free hydrocarbons i.e. at least 10% greater than the concentration of oxygen-free hydrocarbons in the initial pyrolysis product, (ii) a concentration, by weight, of aromatic hydrocarbons i.e. at least 10% greater than the concentration of aromatic hydrocarbons in the initial pyrolysis product, and/or (iii) a cumulative concentration, by weight, of carbon monoxide, carbon dioxide and water i.e. at least 10% greater than the cumulative concentration of carbon monoxide, carbon dioxide and water in the initial pyrolysis product. The temperature of the thermal modification medium is: at least 20 degrees C different than the temperature of the initial pyrolysis product; and less than the temperature of the initial pyrolysis product.