scope:

This standard describes a method for calculating the steady-state air concentrations and mass fluxes of anthropogenic emissions in the vicinity of individual sources or multiple source systems for a distance up to 100 km.

The method of calculation assumes flat terrain, undisturbed dispersion, and wind velocities greater than 1 m·s−1. The effects of buildings or terrain are not taken into account. The computing procedure described in this standard is applicable to gases and dusts (aerosols). The sedimentation process is described. In a first approximation, the computing procedure takes into account dry and wet deposition and chemical conversions. By introducing mean mixing layer heights, restrictions on vertical exchange are taken into account. The sources can be point sources, line sources, area sources, or volume sources.

When the computing method is applied to individual situations, the results are not very meaningful. Meaningful results are only obtained from the statistical evaluation of many individual situations. The computing method is thus primarily used to calculate seasonal or annual means of air concentrations near the ground; it is possible to estimate soil input via determination of the mass fluxes of dry and wet deposition. Data for shorter time periods are insufficiently statistically verified With the limits mentioned, the computing method can be used to calculate percentiles and excess frequencies of hourly means, related to a season or a year. In this case the steady-state air concentration calculated using the model is interpreted as an hourly mean.

The standard can be used to analyze air pollution with respect to emission sources, and can also be applied to multiple source systems.

The computing time is relatively short compared with more complex models, for example the particle model as described in VDI 3945 Part 3. The standard does not replace computing procedures which are incorporated into a closed air pollution evaluation system (for example computing procedures as described in the German TA Luft).

The computing method may not be used to simulate time-dependent emission conditions (for example in conjunction with meteorological time series) by a number of individual situations. In these cases, and when higher accuracy is required, other computing methods have to be used, for example a particle model as described in VDI 3945 Part 3.

The requirements of the input data with respect to sources and meteorological parameters are listed, and procedures are described for determining the vertical wind profile and the dispersion coefficients. Procedures to determine the dispersion categories are described in Standard VDI 3782 Part 6.

The preconditions listed in the various sections of this standard for its applicability have to be checked carefully (see especially Section 4); this requires specialist knowledge.