Abstract
ABSTRACT The source rate is the single most critical input parameter in dispersion models. Determining accurate source rates from workplace processes can be challenging due to interference with work operation and poorly known dilution between the outlet of the particle generator and the measurement point. In this work, we measured the aerosol source rate in a chamber with a steady release of TiO2 particles generated by an aerosol brush generator. The number concentrations measured directly from the particle generator and in the source position near the source spanned three orders of magnitude depending on the relative location and orientation to the source. Moreover, a dispersion factor was calculated based on a single mode fit of the obtained source rates. The dispersion factor takes into account the dispersion and dilution occurring between the measurement point and the source outlet for subsequent modelling. The particle emission rates were implemented in a previously published multi-box aerosol dispersion model using a one-box layout. The modelled concentrations were compared with concentrations measured in three locations in the chamber. We found that using a dispersion factor of one, meaning that at-source dilution or dispersion was not accounted for, the modelled concentrations were 1 to 3 orders of magnitude lower than measured concentrations for all source rates except the source rates measured directly from the aerosol generator. When applying the calculated dispersion factor, thereby correcting the source rate for initial dilution and dispersion, the concentrations were within 0.5 to 2 times the measured concentrations suggesting the use of such a factor to correctly estimate the source rate, and hence the occupational exposure.
Highlights
In occupational health, airborne particles make up a significant part of personal exposures, especially in situations where high-energy processes or chemicals leading to particle formation are used (Hämeri et al, 2009)
For orientation #1, where there was the shortest distance between the outlet of the aerosol generator and the measurement point, as well as the most favourable flow direction, the concentrations were one order of magnitude lower than the reference concentrations at a maximum of 6·105 cm–3 measured by the FMPS
It is reasonable to assume that the higher concentrations in orientations #1, #2, and #3 were due to flow from the aerosol generator being directed directly towards the source measurement point
Summary
Airborne particles make up a significant part of personal exposures, especially in situations where high-energy processes or chemicals leading to particle formation are used (Hämeri et al, 2009). It has been shown that ultrafine particles are present in 60–450 times higher concentrations in industrial sectors and work environments compared to non-occupational environments (Viitanen et al, 2017). The most reliable method to estimate exposure levels in real life work scenarios are well-performed workplace measurements. This includes mapping of concentrations with stationary instrumentation and assessing the personal exposure from the breathing zone using portable samplers and detectors (Viana et al, 2015; Asbach et al, 2017; Ding et al, 2017). The main reason for this is that particle measurements are challenging and expensive to perform and the analysis of the exposure levels requires expert knowledge and proper tools for statistical analysis
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