scope:

This standard is devoted to the calculation of the immission of bioaerosols released by one or more of a plant's specified emission sources. The immission is determined with the aid of a numerical dispersion calculation using a Lagrangian particle model in accordance with standard VDI 3945 Part 3. Gaseous odorants formed by bacteria or moulds, such as MVOC, are not the subject of this standard.

This standard is a standardised, practical tool for determining bioaerosol immission (concentration and deposition) for subsequent assessments and impact analyses. The standard can be employed in connection with licensing procedures, measurement planning and other technical issues relating to the dispersion of bioaerosols.

Assessments and impact analyses themselves are not the subject of this standard. At the time of the drafting of this standard, no provisions (particularly regarding averaging time and investigation period) were available in terms of the type of immission parameters to be referred to. Therefore, this standard states in more general terms the characteristic immission values that can be obtained with the described method.

In a dispersion calculation for bioaerosols, more details can be included than are usually available at the input data stage. This applies particularly to the particle size distribution of the emission and biological transformation rates in the ambient air. To conduct a dispersion calculation, approximations and conventions are therefore necessary. The approaches employed in the standard are such that they tend to yield a deliberate overestimation rather than an undesired underestimation of the concentration (conservative concentration estimate). With growing knowledge in the years to come, it will be possible to refine the approximations and conventions.

Key parts of the standard refer to the provisions of Annex 3 of TA Luft (dispersion calculations for plant-related pollution control) and the recommendations for the performance and quality assurance of dispersion calculations in standard VDI 3783 Part 13. The reference model is that of TA Luft [6]. In special dispersion situations (e.g. cold air flows), case-by-case investigations transcending the scope of TA Luft and the standard may be necessary.

The emission sources can be defined as point, line, area or volume sources with emission rates and exhaust air properties (emission parameters) constant or variable over time. Plume rise of the exhaust can be accounted for in accordance with standard VDI 3782 Part 3 (stacks) or VDI 3784 Part 2 (cooling towers) or with the explicit specification of a rise. The boundary layer is modelled in accordance with standard VDI 3783 Part 8, and the deposition parameters are defined in accordance with standard VDI 3782 Part 5. The terrain is characterised with a mean roughness length. The effect of topographic profile and buildings can be described with simplifying assumptions or explicitly with the aid of prior wind field modelling (VDI 3783 Part 13).

Deposition and sedimentation processes are modelled. To this end, the released bioaerosols, whose atmospheric transport is that of dust, are characterised by means of their aerodynamic diameter, typically by the assignment of a particle size class.

During transport, the physical properties of the bioaerosols can change (e.g. due to agglomeration), as can their biological properties (e.g. their capacity of replication). Furthermore, bioaerosols already deposited on the ground can be stirred up and transported further (resuspension). These processes are either too complex or so far not sufficiently quantifiable for their explicit inclusion in the standardised method. Account is taken of them, where possible, with conservative assumptions. The calculation area for which the immission is determined typically extends to a distance ranging from several hundreds of metres to several tens of kilometres from the emission source with a spatial resolution ranging from several tens of metres to several hundreds of metres.

The meteorological parameters are preferably expressed as a time series. In certain applications, the dispersion calculation can be conducted on the basis of dispersion class statistics gathered over several years.