Models are increasingly used to estimate and pre-emptively calculate the occupational exposure of airborne released particulate matter. Typical two-box models assume instant and fully mixed air volumes, which can potentially cause issues in cases with fast processes, slow air mixing, and/or large volumes. In this study, we present an aerosol dispersion model and validate it by comparing the modelled concentrations with concentrations measured during chamber experiments. We investigated whether a better estimation of concentrations was possible by using different geometrical layouts rather than a typical two-box layout. A one-box, two-box, and two three-box layouts were used. The one box model was found to underestimate the concentrations close to the source, while overestimating the concentrations in the far field. The two-box model layout performed well based on comparisons from the chamber study in systems with a steady source concentration for both slow and fast mixing. The three-box layout was found to better estimate the concentrations and the timing of the peaks for fluctuating concentrations than the one-box or two-box layouts under relatively slow mixing conditions. This finding suggests that industry-relevant scaled volumes should be tested in practice to gain more knowledge about when to use the two-box or the three-box layout schemes for multi-box models.

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The consequences on human health of exposure to airborne fine particles (<2.5 µm) have been a subject of concern for decades, leading notably to the US air quality standards for fine particles in 1987, 1 and the 90s continued providing evidences of adverse effects on health of ultrafine (<100 nm) particulate matter exposure. 2-4 With the emergence of nanotechnology, these concerns now extend to airborne fine and ultrafine particles of engineered nanomaterials 5 (ENMs).The tools currently available for the risk assessment of ENMs and their aerosols are of qualitative or semiquantitative nature only, AbstractA particle exposure experiment inside a large climate-controlled chamber was conducted. Data on spatial and temporal distribution of nanoscale and fine aerosols in the range of mobility diameters 8-600 nm were collected with high resolution, for sodium chloride, fluorescein sodium, and silica particles. Exposure scenarios studied included constant and intermittent source emissions, different aggregation conditions, high (10 h −1 ) and low (3.5 h −1 ) air exchange rates (AERs) corresponding to chamber Reynolds number, respectively, equal to 1 × 10 5 and 3 × 10 4 . Results are presented and analyzed to highlight the main determinants of exposure and to determine whether the assumptions underlying two-box models hold under various scenarios. The main determinants of exposure found were the source generation rate and the ventilation rate. The effect of particles nature was indiscernible, and the decrease of airborne total number concentrations attributable to surface deposition was estimated lower than 2% when the source was active. A near-field/far-field structure of aerosol concentration was always observed for the AER = 10 h −1 but for AER = 3.5 h −1 , a single-field structure was found. The particle size distribution was always homogeneous in space but a general shift of particle diameter (−8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation. K E Y W O R D S aerosol, dispersion, exposure determinants, model validation, nanoparticles, two-box model S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Belut E, Sánchez Jiménez A, Meyer-Plath A, et al. Indoor dispersion of airborne nano and fine particles: Main factors affecting spatial and temporal distribution in the frame of exposure modeling. Indoor Air.