Abstract
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.
Highlights
As the production and use of nanomaterials increases [1,2,3,4], workers are increasingly being exposed to aerosol nanoparticles that were released during the production or reworking [5], with potential adverse health effects [6]
The box model was further developed by Cherrie and Schneider [20], and has been expanded to include several individual compartments in which airflow is restricted by physical barriers, such as walls [10,21,22]
The measured concentrations agreed well within each measurement position with condensation particle counters (CPC) total number concentrations being 0.7 times the corresponding fast mobility particle sizers (FMPS) concentrations; this is due to the lower cut off size in the FMPS and the multi charging agglomerates, which overestimation of the concentration measuredon concentrations agreed wellcauses within some each measurement position withFMPS
Summary
As the production and use of nanomaterials increases [1,2,3,4], workers are increasingly being exposed to aerosol nanoparticles that were released during the production or reworking [5], with potential adverse health effects [6]. Chamber measurements are essential for testing and validating the dispersion models used for exposure assessment. Dispersion of both gases and particles in chambers has previously been studied with included relevant aerosol dynamics and chemistry [7]. The box model assumes a well-mixed chamber where the concentrations are instantly mixed in the entire volume. The ventilation of the well-mixed two-box model was studied by Cherrie et al [23] and has further been analysed to include various setups of local ventilation controls and recirculation by Ganser and Hewett [24], and has been used to model concentrations in workplaces by Koivisto et al [25]
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