Influences on indoor radon concentrations in Riyadh, Saudi Arabia

•Limited information about indoor radon in Riyadh.•Several factors influence Radon level were investigated in 786 dwellings in Riyadh over one year.•Some results are over the action level and are advised to improve their ventilation systems.

The influences on indoor radon concentrations in Riyadh, Saudi Arabia survey was carried out for 786 dwellings. The measurements were obtained by using a passive integrating ionization system with an E-Perm® Electret ion chamber. Radon levels ranged from 1 to 195 Bq m−3, with a mean value of 24.68 Bq m−3, the geometric mean and the geometric standard deviation are 21 and 2 respectively. 98.5% of the results were below the action level recommended by WHO of 100 Bq.m−3. The results were found to vary substantially due to types of houses and rooms, ventilation, seasons and building materials. Radon concentrations were higher in houses with no ventilation systems, and central air conditioners, and were relatively lower in well ventilated houses with red bricks and water air conditioners.