Characteristics and control strategies of indoor particles: An updated review

•This review compiled indoor PM concentration worldwide that mostly exceeded WHO guidelines.•Indoor PM derived mainly from combustion activities, human movement and outdoor sources.•More attention should be paid to the accumulation mode PM due to highly-penetrating and lowly-depositing.•The indoor/outdoor ratio of PM concentration was primarily affected by human activity and ventilation.•Reasonable ventilation, indoor sources control or using filtration-based air cleaners could reduce indoor PM concentration.