In recent years, fine particles have been found to be the cause of various harmful effects on health, and many countries have imposed restrictions on emission of these particles. Fine ash particles are formed during coal combustion in power stations and, if not collected in the air pollution control devices, are emitted into the atmosphere. The fine ash particles can remain airborne for long periods and can result in deleterious health effects when inhaled and deposited in the lungs. Previous studies have shown that combustion of coals of different rank can result in differences in the amount and chemistry of the submicron ash particles. This study examines the variability occurring between the submicron ashes formed from coals of similar rank. Five Australian bituminous coals were burned in a laminar flow drop tube furnace in two different oxygen environments to determine the amount and composition of submicron ash formed. The experimental setup is described and the repeatability of the experiments is discussed. The variability in the submicron ash yield as a percentage of the total ash collected and the submicron ash composition are presented and discussed. This paper presents experimental results rather than a detailed discussion on its interpretation. However, the results indicate that the condensation of evaporated species is responsible for the formation of ash particles smaller than 0.3 mu m. (c) 2004 Elsevier Ltd. All rights reserved.