Impact of PM2.5 in indoor urban environments: A review

Airborne fine particulate matter (PM2.5) is a pollutant that is found in all urban environments. PM2.5 is predominantly generated by traffic and domestic fuel combustion and has significant negative health impacts. The ever-growing urban population spends most of their time in indoor environments where it is exposed to PM2.5 that is brought in from the outdoor environment by ventilation airflow. Several studies show this inflow of outdoor PM2.5, combined with internal sources (e.g. indoor combustion, particle re-suspension) can lead to an I/O ratio above one: indoor air quality is lower than outdoors. The most common approach to limit ventilation inflow of PM2.5 is the use of mechanical ventilation systems with cloth filters that can significantly increase ventilation fan energy consumption. Decreasing exposure to PM2.5 is challenging, requiring a thorough understanding of PM2.5's origin and the interaction between buildings and their surrounding environment. This review of the impact of PM2.5 in indoor urban environments summarizes existing research in this area, specifically, the main PM2.5 sources and sinks in outdoor and indoor urban environments, the PM2.5 exposure limits that are currently applicable throughout the world, the main socio-economic impacts of exposure to PM2.5 and the most promising solutions to minimize indoor exposure.