Comparison of turbulent-diffusion parametersσ v andσ z, evaluated through different experimental tests carried out in the Po Valley in the range (102÷104) m downwind the source, under neutral and unstable conditions, is presented and discussed. Two kinds of methods of tracer dispersion were adopted. The first one dealth with no-lift balloon diffusion in the range (102÷103) m, while the second one was relative to SF6 dispersion in the range (103÷104) m. In the present paper the two sets of data are joined and a single series of best-fit curves covering the whole measured range (102÷104) m is derived. The results show different behaviours forσ y andσ z; in fact, it is possible to extrapolateσ y trends from one set of data (SF6) to the other one (no-lift balloons) without changing the analytical expression and the values of their coefficients. Forσ z, instead, some new considerations are needed. In fact, for the unstable categories here considered (B/C andC) it is necessary to change the analytical form of theσ z trend. This is due to the effect of convection resulting in an increase of dσ z/dx. Finally, the exponent of the sampling time τ, in theσ y vs. τ relationship, was found equal to 0.2, in the range (16÷128) min.