Air pollutants + odours

Forecasts of air pollutants and odours

In general, the Lagrangian particle model AUSTAL2000 or LASAT, whose calculation methods and limits are described in Annex 3 of the Clean Air Act, is used as part of the statutory pollution control licensing of a facility. The selection of an appropriate forecasting model is dependent on a number of factors, which are generally defined by the specific task. Selected important boundary conditions for the selection and use of specific models include the geometry of the emission sources (point, line, area, volume or net-like), the time course of emission (continuous or variable over time), components to be examined (gas or dust forming, odours, inert or reactive), the influence of buildings and the reliefs on the wind field in the micro-and mesoscale, the occurrence of cold air dynamics or the availability of appropriate meteorological input data.

Depending on the task, Müller-BBM uses the following validated and quality assured databases and dispersion models in particular:

  • AUSTAL2000
  • IMMISluft
  • KLAM21
  • P&K 3781
  • P&K 3783
  • IMMISem

Finally, the evaluation of the forecast additional or total charges is made on the basis of recognised and/or statutory predetermined evaluation criteria (Clean Air Act, 39th BImSchV, LAI, etc.). The goal is always to avoid or to minimise adverse environmental impacts and other hazards, significant disadvantages and significant nuisances to the public and the neighbourhood from an air-quality point of view.

The realisation of immission and dispersion calculations, in spite of extensive regulations in this area, is a complex and demanding task. Based on our many years of experience Müller-BBM can help you with the professionally competent, legally secure, and rapid implementation of your specific project.

Modelling of cold air dynamics

So-called cold-air flows (downslope winds) can arise during low wind, cloudless weather after sunset. Cold air refers to air that is near the ground that is colder than the surrounding air due to radiation-induced cooling. Due to the difference in density, the cold air begins to flow downhill on sloped hillsides, creating cold air flows.

Cold air is becoming increasingly important in regional and town planning as well as in environmental impact assessments (EIAs). The influences on the local climate is mostly positive, since cold air can cool the air at night in residential areas. Cold air from emission-free areas is used as a fresh air supply for urban areas and improve local air quality. Sensitive agricultural areas, such as wine and fruit production can however be compromised by cold air reservoirs.

Unfavourable air-quality situations in which air pollutants are emitted into cold air flows and then transported into sensitive areas must be evaluated. If plants exist or are planned in the cold air, then the effects of pollutants and/or odours emitted into the air must be examined in relation to pollution control.

Müller-BBM models the cold air flows using KLAM_21, a forecasting simulation model developed by the German Weather Service (Deutschen Wetterdienst). KLAM_21 takes into account the terrain structure and the surface condition and, if necessary, even small-scale flow obstacles such as embankments. KLAM_21 simulates the temporal evolution of the cold air generation and provides quantitative information on flow rate, flow velocity and cold air layer thickness.

The flow fields from the cold air can be used for simulation with the mesoscale Lagrangian dispersion modelling LASAT. For this purpose, a vertical velocity profile according to VDI 3787 5 "Local cold air" is patterned within the cold air layer, which passes above the cold layer of air in a logarithmic wind profile. The cold air wind fields are assessed in the propagation calculation for those times when cold air situations are present.

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