Combustion of pulverized coals was conducted in a lab-scale drop tube furnace to investigate the formation of submicron particulate matters less than 1.0 mu m in diameter (PM1). Three temperatures, 1473, 1573 and 1723 K were tested. PM, was collected by a low-pressure-impactor, which automatically segregates particulates into seven sizes ranging from 0.03 to 0.76 mu m. Each size was subjected to several techniques for elemental composition and morphology analysis. The results indicate that there are two major portions formed for PM1: particulates smaller than 0.1 mu m and those larger ones. The former portion, termed as PM0.1 in this study, was formed by aggregation of elemental vapors generated by either decomposition of organically bound elements in coal pyrolysis or vaporization of inorganic compounds in char combustion. Sulfates and phosphates dominate this portion. On the other hand, the latter portion in PM1, termed as PM0.1+, was generated containing two kinds of typical particles: one is in a molten solid shape and rich in Al-silicates and another one in the fractal agglomerate form. Liberation of inherent fine minerals (<= 1 mu m) and aggregation of nucleates containing vaporized elements are the two major routes for their formation. PM0.1+ was mainly formed in char combustion. Additionally, both coal type and reaction temperature affected the formation of PM1 greatly. Combustion of bituminous coals produced more the PM1 than the anthracite coal did. Increasing temperature produced more the PM1 as well. (C) 2006 Elsevier Ltd. All rights reserved.