Indoor air quality and particulate matter

There is strong evidence that exposure to airborne particulate matter (PM) causes adverse health effects such as chronic inflammation, asthma, and allergy. Epidemiology studies mainly relied on outdoor PM10 and PM2.5 (particles with diameter smaller than 10 and 2.5 µm, respectively) measurements in fixed monitoring stations, but it is now well known that indoor PM drives personal exposure, as humans spend a large proportion of their time in indoor environments at work and at home. This chapter discusses the spatial distribution of indoor PM concentrations, their seasonal variation, and most influencing factors such as ventilation and indoor and outdoor sources. In the past 30 years, several studies have been published on indoor PM concentration data covering hundreds or even thousands of households. For this chapter, data have been collected from 158 studies worldwide which monitored at least 20 households. Data show that PM2.5 concentrations are the most widely studied with a wide heterogeneity of indoor concentrations found by different studies in different countries around the world. Indoor PM2.5 was rarely found to meet World Health Organization guidelines, and it was mainly impacted by indoor sources such as smoking, heating, cooking, cleaning, and personal care. Infiltration of outdoor PM is also an important contribution to indoor PM, with decreasing impacts moving away from trafficked roads and industrial sites. For the coarser PM fraction, outdoor dust events can also contribute to indoor PM10. Low-income countries and poor-quality housing are also determining factors negatively impacting indoor air quality which raises questions into environmental justice.