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The Effect of Sampling Inlet Direction and Distance on Particle Source Measurements for Dispersion Modelling

Category: Air Pollution Modeling

Volume: 19 | Issue: 5 | Pages: 1114-1125
DOI: 10.4209/aaqr.2018.08.0322
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Alexander Christian Østerskov Jensen 1, Mikko Poikkimäki2, Anders Brostrøm3, Miikka Dal Maso2, Ole John Nielsen4, Thomas Rosenørn5, Andrew Butcher5, Ismo Kalevi Koponen6, Antti Joonas Koivisto1

  • 1 The National Research Centre for the Working Environment, Copenhagen 2100, Denmark
  • 2 Aerosol Physics, Faculty of Natural Sciences, Tampere University of Technology, FI-33101 Tampere, Finland
  • 3 DTU Nanotech, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
  • 4 Department of Chemistry, University of Copenhagen, 2100 Copenhagen, Denmark
  • 5 INFUSER, 2200 Copenhagen, Denmark
  • 6 FORCE Technology, 2605 Brøndby, Denmark

Highlights

  • Particle release measured at various distances and angles from a jet-like source.
  • Single-box modelling and comparison with measured chamber concentrations.
  • Calculation of dispersion factors based on reference source concentrations.
  • Source rates with dispersion factors improved accuracy of modelled concentrations.
  • Provide estimate for uncertainties related to source characterisation.

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.

Keywords

Source measurements Dispersion modelling Chamber studies Aerosol dispersion Occupational health


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