Motivated by growing considerations of the scale, severity, and risks associated with human exposure to indoor particulate matter, this work reviewed existing literature to: (i) identify state-of-the-art experimental techniques used for personal exposure assessment; (ii) compare exposure levels reported for domestic/school settings in different countries (excluding exposure to environmental tobacco smoke and particulate matter from biomass cooking in developing countries); (iii) assess the contribution of outdoor background vs indoor sources to personal exposure; and (iv) examine scientific understanding of the risks posed by personal exposure to indoor aerosols. Limited studies assessing integrated daily residential exposure to just one particle size fraction, ultrafine particles, show that the contribution of indoor sources ranged from 19% to 76%. This indicates a strong dependence on resident activities, source events and site specificity, and highlights the importance of indoor sources for total personal exposure. Further, it was assessed that 10-30% of the total burden of disease from particulate matter exposure was due to indoor-generated particles, signifying that indoor environments are likely to be a dominant environmental factor affecting human health. However, due to challenges associated with conducting epidemiological assessments, the role of indoor-generated particles has not been fully acknowledged, and improved exposure/risk assessment methods are still needed, together with a serious focus on exposure control.

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A stochastic lung model is proposed for aerosol deposition calculations. Airway geometry is selected randomly to reflect intrasubject variations in the human airway system. This may also be adjusted to take intersubject variations into account. The statistical analysis of the human airway geometry used is based on morphometric data measured at the Lovelace Inhalation Toxicology Research Institute. Average values and distributions of airway diameters and lengths, distributions of branching angles and criteria for termination of the pathway (when the alveolar region is reached) are presented. Correlations between the cross sections of tubes of succeeding generations and those between diameters and lengths of the same generation are also given.