In Annex "Dispersion Calculation" of the Technical Instruction on Air Quality Control (TA Luft), a Lagrangian particle model according to the standard VDI 3945 Part 3 and further requirements are specified for the dispersion calculation.
The programs AUSTAL and AUSTAL2000 are an exemplary implementation of the requirements of this Annex. AUSTAL (starting with version 3) refers to the TA Luft draft 2020 and is the successor of AUSTAL2000 (ending with version 2), which refers to the TA Luft 2002. The programs AUSTAL and AUSTAL2000 were developed by Janicke Consulting on behalf of the German Environment Agency (UFOPLAN projects 3714 43 204 0 and 200 43 256 and UBA project 94835).
The specifications of the Annex "Dispersion Calculation" themself are already sufficient for a computational implementation of the prescribed algorithms. AUSTAL / AUSTAL2000 is provided by the Federal Environmental Agency as a free reference implementation. It can be used both for practical applications and to check other programs that implement the Annex "Dispersion Calculation" of the TA Luft.