Metphomod includes modules for (1) fluid dynamics, consisting of (a) transport, (b) turbulent exchange, (c) pressure; (2) soil-atmosphere interchanges; (3) solar radiation; (4) IR radiation; (5) gas phase chemistry; (6) emissions; (7) deposition. Mostly standard methods which were published and discussed in the literature were used for the implementation of these modules. They are described in full detail in Perego (1996) for version 1 of Metphomod . In the following subsections the methods used in version 2 of Metphomod are described.