“…In Section 2, we introduce in some detail a basic model starting from the main ideas of macroscopic modelling of filtration in porous media (Barenblatt et al 1990, Nield andBejan 1992). Next, we shall present a qualitative discussion of the asymptotic behavior of the solutions, for unbounded domain x > 0, by using scaling arguments similar to the ones used in Hilhorst et al (1996), Aregba-Driollet et al (2004), and Guarguaglini and Natalini (2005b). In the present case we find that, for large values of the reaction rate, and small values of the external concentration of SO 2 , the solutions still present formation of sharp fronts, as in the case of system (2).…”