A novel two-stage alumina reactor system is developed for studying particulate matter (PM) emission from in situ volatiles combustion. It enables the generation of in situ volatiles at different pyrolysis temperatures (up to 1300 degrees C) and the subsequent combustion of in situ volatiles in air and oxyfuel at 1300 degrees C. It is found that the PM emitted from volatiles combustion contains only PM with aerodynamic diameter <1 mu m (PM1) and has a unimodal distribution. An increase in pyrolysis temperature from 1100 to 1300 degrees C results in a substantial increase in PM1 yield and a shift of fine mode diameter from 0.043 to 0.108 Jim. The PM1 emitted from the volatiles generated at 1100 degrees C mainly consists of Na, K, S, and P. For PM, emitted from the volatiles generated at 1300 degrees C, there are substantial increases in the yield of Na, K, and P; in addition, Mg and Si are present in PM1 because of the release of these inorganic species from biosolid into the volatiles. For trace elements, increasing pyrolysis temperature from 1100 to 1300 degrees C not only increases the As and Cd yields in PM1 but also results in the presence of Cr, Cu, and Mn in PM, because of increasing As and Cd volatility and the release of Cr, Cu, and Mn from biosolid into the volatiles. The yields of V and Pb remained unchanged, and there is no Ti, Ni, and Co present in the PM1. Changing the combustion atmosphere from air to oxyfuel causes a slight increase in PM, yield due to increased formation of alkali sulfates and enhanced formation of P4010 but results in no changes in the yields and particle size distributions of trace elements. Further analysis indicates the Na, K, S, and CI are present in the PM1 emitted from the combustion of volatiles produced at 1100 degrees C in the form of Na and K sulfates and Cl while P is present in the form of P4O10. The P in PM1 is present in the forms of Na, K, and Mg metaphosphates and P4O10 where higher proportion of P4O10 is formed in PM1 when pyrolysis temperature increases to 1300 degrees C. It is also evident that (Na, K)PO3 and P4O10 vapors can react with the alumina reactor tube to form alkali aluminophosphate glass which is then retained in the furnace, leading to only a fraction of Na and K in the volatiles being collected as PM1 after combustion.