Abstract The present one-year study is concerned with the degree of relationship between the changes in quantity and quality of outdoor and indoor settled dust in Abu Qurqas town in Middle Egypt and the combustion of cane bagasse in boiler furnaces in a sugar factory located in the same town. It can be suggested that this process is responsible for increasing the rate of outdoor and indoor deposition of combustible matter by 2–8 and 2–7 times, respectively, during the period of December–April. However, it can be suggested also that the same process has a limited role, as it is a source of ash content of both outdoor and indoor settled dust and is ineffective in polluting the two environments with calcium, chloride and sulphate ions and tar fraction. Indoor levels of settled dust and its constituents were found to be lowest during cold months. This causes the indoor levels of combustible matter resulting from the sugar factory to be lower than the outdoor levels by 41–45% during December–March and by 28% during April which is a relatively warm month in Middle Egypt.